path: root/docs/index.rst

.. This work is licensed under a Creative Commons Attribution 4.0 International License.
.. http://creativecommons.org/licenses/by/4.0
.. Copyright © 2017 AT&T Intellectual Property. All rights reserved.

Logging Enhancements Project
==================================================
.. contents::
   :depth: 3
..

ONAP consists of many components and containers, and consequently writes
to many logfiles. The volume of logger output may be enormous,
especially when debugging. Large, disparate logfiles are difficult to
monitor and analyze, and tracing requests across many files, file
systems and containers is untenable without tooling. 

The problem of decentralized logger output is addressed by analytics
pipelines such as \ `*Elastic
Stack* <https://www.elastic.co/products>`__ (ELK). Elastic Stack
consumes logs, indexes their contents
in \ `*Elasticsearch* <https://www.elastic.co/products/elasticsearch>`__,
and makes them accessible, queryable and navigable via a sophisticated
UI, \ `*Kibana
Discover* <https://www.elastic.co/guide/en/kibana/current/discover.html>`__.
This elevates the importance of standardization and machine-readability.
Logfiles can remain browsable, but output can be simplified.

Logger configurations in ONAP are diverse and idiosyncratic. Addressing
these issues will prevent costs from being externalized to consumers
such as analytics. It also affords the opportunity to remedy any issues
with the handling and propagation of contextual information such as
transaction identifiers (presently passed as \ **X-ECOMP-RequestID **-
to be\ ** X-ONAP-RequestID**). This propagation is critical to tracing
requests as they traverse ONAP and related systems, and is the basis for
many analytics functions. 

Rationalized logger configuration and output also paves the way for
other high-performance logger transports, including publishing directly
to analytics via SYSLOG
(`*RFC3164* <https://www.ietf.org/rfc/rfc3164.txt>`__, \ `*RFC5425* <https://www.ietf.org/rfc/rfc5425.txt>`__, \ `*RFC5426* <https://www.ietf.org/rfc/rfc5426.txt>`__)
and streams, and mechanisms for durability.

Each change is believed to be individually beneficial:

1. The intention is to consolidate the required setup within this
   project however some changes and bug fixes might have to be applied
   in the relative component project, requiring each components'
   co-operation on the contribution.

2. There is an economy of scale if everything can happen under a single
   remit.

3. Standardization benefits all, including those who want to deviate
   from defaults.

ONAP Application Logging Guidelines v1.1
========================================

Introduction
------------

The purpose of ONAP logging is to capture information needed to operate,
troubleshoot and report on the performance of the ONAP platform and its
constituent components. Log records may be viewed and consumed directly
by users and systems, indexed and loaded into a datastore, and used to
compute metrics and generate reports. 

The processing of a single client request will often involve multiple
ONAP components and/or subcomponents (interchangeably referred to as
application in this document). The ability to track flows across
components is critical to understanding ONAPs behavior and performance.
ONAP logging uses a universally unique RequestID value in log records to
track the processing of every client request through all the ONAP
components involved in its processing.

A reference configuration of \ `*Elastic
Stack * <https://www.elastic.co/products>`__\ can be deployed
using \ `*ONAP Operations
Manager* <https://wiki.onap.org/display/DW/ONAP+Operations+Manager+Project>`__. 

This document gives conventions you can follow to generate conformant,
indexable logging output from your component.

How to Log
----------

ONAP prescribes conventions. The use of certain APIs and providers is
recommended, but they are not mandatory. Most components log
via \ `*EELF* <https://github.com/att/EELF>`__ or `*SLF4J* <https://www.slf4j.org/>`__ to
a provider
like \ `*Logback* <https://logback.qos.ch/>`__ or `*Log4j* <https://logging.apache.org/log4j/2.x/>`__.

****
EELF
****

EELF is the\ **Event and Error Logging Framework**, described
at \ `*https://github.com/att/EELF* <https://github.com/att/EELF>`__.

EELF abstracts your choice of logging provider, and decorates the
familiar Logger contracts with features like:

-  Localization.

-  Error codes. 

-  Generated wiki documentation.

-  Separate audit, metric, security and debug logs.

EELF is a facade, so logging output is configured in two ways:

1. By selection of a logging provider such as Logback or Log4j,
   typically via the classpath. 

2. By way of a provider configuration document,
   typically \ **logback.xml** or **log4j.xml**.
   See \ `*Providers* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-Providers>`__.

*****
SLF4J
*****

`*SLF4J* <https://www.slf4j.org/>`__ is a logging facade, and a humble
masterpiece. It combines what's common to all major, modern Java logging
providers into a single interface. This decouples the caller from the
provider, and encourages the use of what's universal, familiar and
proven. 

EELF also logs via SLF4J's abstractions.

*********
Providers
*********

Logging providers are normally enabled by their presence in the
classpath. This means the decision may have been made for you, in some
cases implicitly by dependencies. If you have a strong preference then
you can change providers, but since the implementation is typically
abstracted behind EELF or SLF4J, it may not be worth the effort.

*******
Logback
*******

Logback is the most commonly used provider. It is generally configured
by an XML document named \ **logback.xml**.
See \ `*Configuration* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-Configuration>`__.

*************
Log4j 2.X
*************

Log4j 2.X is somewhat less common than Logback, but equivalent. It is
generally configured by an XML document
named \ **log4j.xml**. See \ `*Configuration* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-Configuration>`__.

*********
Log4j 1.X
*********

Avoid, since 1.X is EOL, and since it does not support escaping, so its
output may not be
machine-readable. See \ `*https://logging.apache.org/log4j/1.2/* <https://logging.apache.org/log4j/1.2/>`__.

This affects existing OpenDaylight-based components like SDNC and APPC,
since ODL releases prior
to \ `*Carbon* <https://www.opendaylight.org/what-we-do/current-release>`__ bundle
Log4j 1.X, and make it difficult to replace. The \ `*Common Controller
SDK
Project* <https://wiki.onap.org/display/DW/Common+Controller+SDK+Project>`__ project
targets ODL Carbon, so the problem should resolve in time.

What to Log
===========

The purpose of logging is to capture diagnostic information.

An important aspect of this is analytics, which requires tracing of
requests between components. In a large, distributed system such as ONAP
this is critical to understanding behavior and performance. 

Messages, Levels, Components and Categories
--------------------------------------------

It isn't the aim of this document to reiterate the basics, so advice
here is general: 

-  Use a logger. Consider using EELF. 

-  Write log messages in English.

-  Write meaningful messages. Consider what will be useful to consumers
   of logger output. 

-  Use errorcodes to characterise exceptions.

-  Log at the appropriate level. Be aware of the volume of logs that
   will be produced.

-  Log in a machine-readable format. See Conventions.

-  Log for analytics as well as troubleshooting.

Others have written extensively on this: 

-  `*http://www.masterzen.fr/2013/01/13/the-10-commandments-of-logging/* <http://www.masterzen.fr/2013/01/13/the-10-commandments-of-logging/>`__

-  `*https://www.loggly.com/blog/how-to-write-effective-logs-for-remote-logging/* <https://www.loggly.com/blog/how-to-write-effective-logs-for-remote-logging/>`__

-  And so on.

Context
-------

**TODO: more on the importance of transaction ID propagation.**

MDCs
====


A Mapped Diagnostic Context (MDC) allows an arbitrary string-valued
attribute to be attached to a Java thread. The MDC's value is then
emitted with each log message. The set of MDCs associated with a log
message is serialized as unordered name-value pairs (see `*Text
Output* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-TextOutput>`__).

A good discussion of MDCs can be found
at \ `*https://logback.qos.ch/manual/mdc.html* <https://logback.qos.ch/manual/mdc.html>`__. 

**MDCs:**

-  Must be set as early in invocation as possible. 

-  Must be unset on exit. 

Logging
-------

**Via SLF4J:**

+------+-------------------------------------------------------------------------------------+
| 1    | import java.util.UUID;                                                              |
|      |                                                                                     |
| 2    | import org.slf4j.Logger;                                                            |
|      |                                                                                     |
| 3    | import org.slf4j.LoggerFactory;                                                     |
|      |                                                                                     |
| 4    | import org.slf4j.MDC;                                                               |
|      |                                                                                     |
| 5    | // ...                                                                              |
|      |                                                                                     |
| 6    | final Logger logger = LoggerFactory.getLogger(this.getClass());                     |
|      |                                                                                     |
| 7    | MDC.put("SomeUUID", UUID.randomUUID().toString());                                  |
|      |                                                                                     |
| 8    | try {                                                                               |
|      |                                                                                     |
| 9    |     logger.info("This message will have a UUID-valued 'SomeUUID' MDC attached.");   |
|      |                                                                                     |
| 10   |     // ...                                                                          |
|      |                                                                                     |
| 11   | }                                                                                   |
|      |                                                                                     |
| 12   | finally {                                                                           |
|      |                                                                                     |
| 13   |     MDC.clear();                                                                    |
|      |                                                                                     |
| 14   | }                                                                                   |
+------+-------------------------------------------------------------------------------------+

EELF doesn't directly support MDCs, but SLF4J will receive any MDC that
is set (where **com.att.eelf.configuration.SLF4jWrapper** is the
configured EELF provider):

+------+-------------------------------------------------------------------------------------+
| 1    | import java.util.UUID;                                                              |
|      |                                                                                     |
| 2    | import org.slf4j.Logger;                                                            |
|      |                                                                                     |
| 3    | import org.slf4j.LoggerFactory;                                                     |
|      |                                                                                     |
| 4    | import org.slf4j.MDC;                                                               |
|      |                                                                                     |
| 5    | import com.att.eelf.configuration.EELFLogger;                                       |
|      |                                                                                     |
| 6    | import com.att.eelf.configuration.EELFManager;                                      |
|      |                                                                                     |
| 7    | // ...                                                                              |
|      |                                                                                     |
| 8    | final EELFLogger logger = EELFManager.getInstance().getLogger(this.getClass());     |
|      |                                                                                     |
| 9    | MDC.put("SomeUUID", UUID.randomUUID().toString());                                  |
|      |                                                                                     |
| 10   | try {                                                                               |
|      |                                                                                     |
| 11   |     logger.info("This message will have a UUID-valued 'SomeUUID' MDC attached.");   |
|      |                                                                                     |
| 12   |     // ...                                                                          |
|      |                                                                                     |
| 13   | }                                                                                   |
|      |                                                                                     |
| 14   | finally {                                                                           |
|      |                                                                                     |
| 15   |     MDC.clear();                                                                    |
|      |                                                                                     |
| 16   | }                                                                                   |
+------+-------------------------------------------------------------------------------------+

Serializing
-----------

Output of MDCs must ensure that:

-  All reported MDCs are logged with both name AND value. Logging output
   should not treat any MDCs as special.

-  All MDC names and values are escaped.

Escaping in Logback configuration can be achieved with:

+-----+------------------------------------------------------------------+
| 1   | %replace(%replace(%mdc){'\\t','\\\\\\\\t'}){'\\n','\\\\\\\\n'}   |
+-----+------------------------------------------------------------------+

MDC - RequestID
---------------

This is often referred to by other names, including "Transaction ID",
and one of several (pre-standardization) REST header names
including \ **X-ECOMP-RequestID** and **X-ONAP-RequestID**.

ONAP logging uses a universally unique "**RequestID"** value in log
records to track the processing of each client request across all the
ONAP components involved in its processing.

This value:

-  Is logged as a \ **RequestID** MDC. 

-  Is propagated between components in REST calls as
   an \ **X-TransactionID** HTTP header.

Receiving the \ **X-TransactionID** will vary by component according to
APIs and frameworks. In general:

+-----+--------------------------------------------------------------------------+
| 1   | import javax.ws.rs.core.HttpHeaders;                                     |
|     |                                                                          |
| 2   | // ...                                                                   |
|     |                                                                          |
| 3   | final HttpHeaders headers = ...;                                         |
|     |                                                                          |
| 4   | // ...                                                                   |
|     |                                                                          |
| 5   | String txId = headers.getRequestHeaders().getFirst("X-TransactionID");   |
|     |                                                                          |
| 6   | if (StringUtils.isBlank(txId)) {                                         |
|     |                                                                          |
| 7   |     txId = UUID.randomUUID().toString();                                 |
|     |                                                                          |
| 8   | }                                                                        |
|     |                                                                          |
| 9   | MDC.put("RequestID", txID);                                              |
+-----+--------------------------------------------------------------------------+

Setting the \ **X-TransactionID** likewise will vary. For example:

+-----+---------------------------------------------------+
| 1   | final String txID = MDC.get("RequestID");         |
|     |                                                   |
| 2   | HttpURLConnection cx = ...;                       |
|     |                                                   |
| 3   | // ...                                            |
|     |                                                   |
| 4   | cx.setRequestProperty("X-TransactionID", txID);   |
+-----+---------------------------------------------------+

MDC - InvocationID
------------------

**InvocationID** is similar to \ **RequestID**, but
where \ **RequestID** correlates records relating a single, top-level
invocation of ONAP as it traverses many
systems, \ **InvocationID** correlates log entries relating to a single
invocation of a single component. Typically this means via REST, but in
certain cases an \ **InvocationID** may be allocated without a new
invocation, e.g. when a request is retried.

**RequestID** and** InvocationID** allow an execution graph to be
derived. This requires that:

-  The relationship between \ **RequestID** and **InvocationID** is
   reported. 

-  The relationship between caller and recipient is reported for each
   invocation.

The proposed approach is that:

-  Callers:

   -  Issue a new, unique \ **InvocationID** UUID for each downstream
      call they make. 

   -  Log the new \ **InvocationID**, indicating the intent to invoke:

      -  With Markers \ **INVOKE**, and \ **SYNCHRONOUS** if the
         invocation is synchronous.

      -  With their own \ **InvocationID** still set as an MDC.

   -  Pass the \ **InvocationID** as an \ **X-InvocationID** REST
      header.

-  Invoked components:

   -  Retrieve the \ **InvocationID** from REST headers upon invocation,
      or generate a UUID default. 

   -  Set the \ **InvocationID** MDC.

   -  Write a log entry with the Marker \ **ENTRY**. (In EELF this will
      be to the AUDIT log).

   -  Act as per Callers in all downstream requests. 

   -  Write a log entry with the Marker \ **EXIT** upon return. (In EELF
      this will be to the METRIC log).

   -  Unset all MDCs on exit.

That seems onerous, but:

-  It's only a few calls. 

-  It can be largely abstracted in the case of EELF logging.

**TODO: code.**

MDCs - the Rest
---------------

Other MDCs are logged in a wide range of contexts.

Certain MDCs and their semantics may be specific to EELF log types.

**TODO: cross-reference EELF output to v1 doc.**

+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| **ID**   | **MDC**               | **Description**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | **Required**   | **EELF Audit**   | **EELF Metric**   | **EELF Error**   | **EELF Debug**   |
+==========+=======================+================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+================+==================+===================+==================+==================+
| 1        | BeginTimestamp        | Date-time that processing activities being logged begins. The value should be represented in UTC and formatted per ISO 8601, such as œ2015-06-03T13:21:58+00:00. The time should be shown with the maximum resolution available to the logging component (e.g., milliseconds, microseconds) by including the appropriate number of decimal digits. For example, when millisecond precision is available, the date-time value would be presented as, as œ2015-06-03T13:21:58.340+00:00.                                                                                       | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 2        | EndTimestamp          | Date-time that processing for the request or event being logged ends. Formatting rules are the same as for the BeginTimestamp field above.                                                                                                                                                                                                                                                                                                                                                                                                                                     | Y              |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | In the case of a request that merely logs an event and has not subsequent processing, the EndTimestamp value may equal the BeginTimestamp value.                                                                                                                                                                                                                                                                                                                                                                                                                               |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 3        | ElapsedTime           | This field contains the elapsed time to complete processing of an API call or transaction request (e.g., processing of a message that was received). This value should be the difference between. EndTimestamp and BeginTimestamp fields and must be expressed in milliseconds.                                                                                                                                                                                                                                                                                                | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 4        | ServiceInstanceID     | This field is optional and should only be included if the information is readily available to the logging component.                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | | Transaction requests that create or operate on a particular instance of a service/resource can                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                |                  |                   |                  |                  |
|          |                       | | identify/reference it via a unique œserviceInstanceID value. This value can be used as a primary key for                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                |                  |                   |                  |                  |
|          |                       | | obtaining or updating additional detailed data about that specific service instance from the inventory                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                |                  |                   |                  |                  |
|          |                       | | (e.g., AAI). In other words:                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |                |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | -  In the case of processing/logging a transaction request for creating a new service instance, the serviceInstanceID value is determined by either a) the MSO client and passed to MSO or b) by MSO itself upon receipt of a such a request.                                                                                                                                                                                                                                                                                                                                  |                |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | -  In other cases, the serviceInstanceID value can be used to reference a specific instance of a service as would happen in a œMACD-type request.                                                                                                                                                                                                                                                                                                                                                                                                                             |                |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | -  ServiceInstanceID is associated with a requestID in log records to facilitate tracing its processing over multiple requests and for a specific service instance. Its value may be left œempty in subsequent record to the 1 st record where a requestID value is associated with the serviceInstanceID value.                                                                                                                                                                                                                                                              |                |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | NOTE: AAI wont have a serviceInstanceUUID for every service instance. For example, no serviceInstanceUUID is available when the request is coming from an application that may import inventory data.                                                                                                                                                                                                                                                                                                                                                                          |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 5        | VirtualServerName     | Physical/virtual server name. Optional: empty if determined that its value can be added by the agent that collects the log files collecting.                                                                                                                                                                                                                                                                                                                                                                                                                                   |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 6        | ServiceName           | For Audit log records that capture API requests, this field contains the name of the API invoked at the component creating the record (e.g., Layer3ServiceActivateRequest).                                                                                                                                                                                                                                                                                                                                                                                                    | Y              |                  |                   |                  |                  |
|          |                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
|          |                       | For Audit log records that capture processing as a result of receipt of a message, this field should contain the name of the module that processes the message.                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 7        | PartnerName           | This field contains the name of the client application user agent or user invoking the API if known.                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 8        | StatusCode            | This field indicates the high level status of the request. It must have the value COMPLETE when the request is successful and ERROR when there is a failure.                                                                                                                                                                                                                                                                                                                                                                                                                   | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 9        | ResponseCode          | This field contains application-specific error codes. For consistency, common error categorizations should be used.                                                                                                                                                                                                                                                                                                                                                                                                                                                            |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 10       | ResponseDescription   | This field contains a human readable description of the \ **ResponseCode**.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                |                  |                   |                  | 11               |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 11       | InstanceUUID          | If known, this field contains a universally unique identifier used to differentiate between multiple instances of the same (named) log writing service/application. Its value is set at instance creation time (and read by it, e.g., at start/initialization time from the environment). This value should be picked up by the component instance from its configuration file and subsequently used to enable differentiation of log records created by multiple, locally load balanced ONAP component or subcomponent instances that are otherwise identically configured.   |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 12       | Severity              | Optional: 0, 1, 2, 3 see \ `*Nagios* <https://en.wikipedia.org/wiki/Nagios>`__ monitoring/alerting for specifics/details.                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 13       | TargetEntity          | It contains the name of the ONAP component or sub-component, or external entity, at which the operation activities captured in this metrics log record is invoked.                                                                                                                                                                                                                                                                                                                                                                                                             | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 14       | TargetServiceName     | It contains the name of the API or operation activities invoked at the TargetEntity.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 15       | Server                | This field contains the Virtual Machine (VM) Fully Qualified Domain Name (FQDN) if the server is virtualized. Otherwise, it contains the host name of the logging component.                                                                                                                                                                                                                                                                                                                                                                                                   | Y              |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 16       | ServerIPAddress       | This field contains the logging component host servers IP address if known (e.g. Jetty containers listening IP address). Otherwise it is empty.                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 17       | ServerFQDN            | Unclear, but possibly duplicating one or both of \ **Server** and **ServerIPAddress**.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 18       | ClientIPAddress       | This field contains the requesting remote client applications IP address if known. Otherwise this field can be empty.                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 19       | ProcessKey            | This field can be used to capture the flow of a transaction through the system by indicating the components and operations involved in processing. If present, it can be denoted by a comma separated list of components and applications.                                                                                                                                                                                                                                                                                                                                     |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 20       | RemoteHost            | Unknown.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 21       | AlertSeverity         | Unknown.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 22       | TargetVirtualEntity   | Unknown                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 23       | ClassName             | Defunct. Doesn't require an MDC.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 24       | ThreadID              | Defunct. Doesn't require an MDC.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 25       | CustomField1          | (Defunct now that MDCs are serialized as NVPs.)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 26       | CustomField2          | (Defunct now that MDCs are serialized as NVPs.)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 27       | CustomField3          | (Defunct now that MDCs are serialized as NVPs.)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+
| 28       | CustomField4          | (Defunct now that MDCs are serialized as NVPs.)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                |                  |                   |                  |                  |
+----------+-----------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+------------------+-------------------+------------------+------------------+

Examples
--------

******
SDC-BE
******

20170907: audit.log

+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| root@ip-172-31-93-160:/dockerdata-nfs/onap/sdc/logs/SDC/SDC-BE# tail -f audit.log                                                                                                                                             |
|                                                                                                                                                                                                                               |
| 2017-09-07T18:04:03.679Z\|\|\|\|\|qtp1013423070-72297\|\|ASDC\|SDC-BE\|\|\|\|\|\|\|N/A\|INFO\|\|\|\|10.42.88.30\|\|o.o.s.v.r.s.VendorLicenseModelsImpl\|\|ActivityType=<audit>, Desc=< --Audit-- Create VLM. VLM Name: lm4>   |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

**TODO: this is the earlier output format. Let's find an example which matches the latest line format.**

Markers
=======

Markers differ from MDCs in two important ways:

1. They have a name, but no value. They are a tag. 

2. Their scope is limited to logger calls which specifically reference
   them; they are
   not \ `*ThreadLocal* <https://docs.oracle.com/javase/8/docs/api/java/lang/ThreadLocal.html>`__. 

Logging
-------

**********
Via SLF4J:
**********

+-----+-----------------------------------------------------------------------+
| 1   | import org.slf4j.Logger;                                              |
|     |                                                                       |
| 2   | import org.slf4j.LoggerFactory;                                       |
|     |                                                                       |
| 3   | import org.slf4j.Marker;                                              |
|     |                                                                       |
| 4   | import org.slf4j.MarkerFactory;                                       |
|     |                                                                       |
| 5   | // ...                                                                |
|     |                                                                       |
| 6   | final Logger logger = LoggerFactory.getLogger(this.getClass());       |
|     |                                                                       |
| 7   | final Marker marker = MarkerFactory.getMarker("MY\_MARKER");          |
|     |                                                                       |
| 8   | logger.warn(marker, "This warning has a 'MY\_MARKER' annotation.");   |
+-----+-----------------------------------------------------------------------+

EELF does not allow Markers to be set directly. See notes on
the \ **InvocationID** MDC.

Serializing
-----------

Marker names also need to be escaped, though they're much less likely to
contain problematic characters than MDC values.

Escaping in Logback configuration can be achieved with:

+-----+---------------------------------------------------------------------+
| 1   | %replace(%replace(%marker){'\\t','\\\\\\\\t'}){'\\n','\\\\\\\\n'}   |
+-----+---------------------------------------------------------------------+

Marker - ENTRY
--------------

This should be reported as early in invocation as possible, immediately
after setting the \ **RequestID** and **InvocationID** MDCs.

It can be automatically set by EELF, and written to the AUDIT log. 

It must be manually set otherwise. 

*****
EELF
*****

**EELF**

+-----+----------+
| 1   | //TODO   |
+-----+----------+

*****
SLF4J
*****

**SLF4J**

+-----+------------------------------------------------------------------------+
| 1   | public static final Marker ENTRY = MarkerFactory.getMarker("ENTRY");   |
|     |                                                                        |
| 2   | // ...                                                                 |
|     |                                                                        |
| 3   | final Logger logger = LoggerFactory.getLogger(this.getClass());        |
|     |                                                                        |
| 4   | logger.debug(ENTRY, "Entering.");                                      |
+-----+------------------------------------------------------------------------+

Marker - EXIT
-------------

This should be reported as late in invocation as possible, immediately
before unsetting the \ **RequestID** and **InvocationID** MDCs.

It can be automatically reported by EELF, and written to the METRIC
log. 

It must be manually set otherwise.

*****
EELF
*****

**EELF**

+-----+----------+
| 1   | //TODO   |
+-----+----------+

******
SLF4J
******

**SLF4J**

+-----+----------------------------------------------------------------------+
| 1   | public static final Marker EXIT = MarkerFactory.getMarker("EXIT");   |
|     |                                                                      |
| 2   | // ...                                                               |
|     |                                                                      |
| 3   | final Logger logger = LoggerFactory.getLogger(this.getClass());      |
|     |                                                                      |
| 4   | logger.debug(EXIT, "Exiting.");                                      |
+-----+----------------------------------------------------------------------+

Marker - INVOKE
---------------

This should be reported by the caller of another ONAP component via
REST, including a newly allocated \ **InvocationID**, which will be
passed to the caller. 

******
SLF4J
******

**SLF4J**

+------+--------------------------------------------------------------------------+
| 1    | public static final Marker INVOKE = MarkerFactory.getMarker("INVOKE");   |
|      |                                                                          |
| 2    | // ...                                                                   |
|      |                                                                          |
| 3    |                                                                          |
|      |                                                                          |
| 4    | // Generate and report invocation ID.                                    |
|      |                                                                          |
| 5    |                                                                          |
|      |                                                                          |
| 6    | final String invocationID = UUID.randomUUID().toString();                |
|      |                                                                          |
| 7    | MDC.put(MDC\_INVOCATION\_ID, invocationID);                              |
|      |                                                                          |
| 8    | try {                                                                    |
|      |                                                                          |
| 9    |     logger.debug(INVOKE\_SYNCHRONOUS, "Invoking synchronously ... ");    |
|      |                                                                          |
| 10   | }                                                                        |
|      |                                                                          |
| 11   | finally {                                                                |
|      |                                                                          |
| 12   |     MDC.remove(MDC\_INVOCATION\_ID);                                     |
|      |                                                                          |
| 13   | }                                                                        |
|      |                                                                          |
| 14   |                                                                          |
|      |                                                                          |
| 15   | // Pass invocationID as HTTP X-InvocationID header.                      |
|      |                                                                          |
| 16   |                                                                          |
|      |                                                                          |
| 17   | callDownstreamSystem(invocationID, ... );                                |
+------+--------------------------------------------------------------------------+

**TODO: EELF, without changing published APIs.**

Marker - SYNCHRONOUS
------------------------

This should accompany \ **INVOKE** when the invocation is synchronous.

******
SLF4J
******

**SLF4J**

+------+-------------------------------------------------------------------------+
| 1    | public static final Marker INVOKE\_SYNCHRONOUS;                         |
|      |                                                                         |
| 2    | static {                                                                |
|      |                                                                         |
| 3    |     INVOKE\_SYNCHRONOUS = MarkerFactory.getMarker("INVOKE");            |
|      |                                                                         |
| 4    |     INVOKE\_SYNCHRONOUS.add(MarkerFactory.getMarker("SYNCHRONOUS"));    |
|      |                                                                         |
| 5    | }                                                                       |
|      |                                                                         |
| 6    | // ...                                                                  |
|      |                                                                         |
| 7    |                                                                         |
|      |                                                                         |
| 8    | // Generate and report invocation ID.                                   |
|      |                                                                         |
| 9    |                                                                         |
|      |                                                                         |
| 10   | final String invocationID = UUID.randomUUID().toString();               |
|      |                                                                         |
| 11   | MDC.put(MDC\_INVOCATION\_ID, invocationID);                             |
|      |                                                                         |
| 12   | try {                                                                   |
|      |                                                                         |
| 13   |     logger.debug(INVOKE\_SYNCHRONOUS, "Invoking synchronously ... ");   |
|      |                                                                         |
| 14   | }                                                                       |
|      |                                                                         |
| 15   | finally {                                                               |
|      |                                                                         |
| 16   |     MDC.remove(MDC\_INVOCATION\_ID);                                    |
|      |                                                                         |
| 17   | }                                                                       |
|      |                                                                         |
| 18   |                                                                         |
|      |                                                                         |
| 19   | // Pass invocationID as HTTP X-InvocationID header.                     |
|      |                                                                         |
| 20   |                                                                         |
|      |                                                                         |
| 21   | callDownstreamSystem(invocationID, ... );                               |
+------+-------------------------------------------------------------------------+

**TODO: EELF, without changing published APIs.**

Errorcodes
==========

Errorcodes are reported as MDCs. 

Exceptions should be accompanied by an errrorcode. Typically this is
achieved by incorporating errorcodes into your exception hierarchy and
error handling. ONAP components generally do not share this kind of
code, though EELF defines a marker interface (meaning it has no
methods) \ **EELFResolvableErrorEnum**.

A common convention is for errorcodes to have two components:

1. A \ **prefix**, which identifies the origin of the error. 

2. A \ **suffix**, which identifies the kind of error.

Suffixes may be numeric or text. They may also be common to more than
one component.

For example:

+-----+-------------------------------+
| 1   | COMPONENT\_X.STORAGE\_ERROR   |
+-----+-------------------------------+

Output Format
-------------

Several considerations:

1. Logs should be human-readable (within reason). 

2. Shipper and indexing performance and durability depends on logs that
   can be parsed quickly and reliably.

3. Consistency means fewer shipping and indexing rules are required.

***********
Text Output
***********

ONAP needs to strike a balance between human-readable and
machine-readable logs. This means:

-  The use of tab (**\\t**) as a delimiter.

-  Escaping all messages, exceptions, MDC values, Markers, etc. to
   replace tabs in their content.

-  Escaping all newlines with \ **\\n** so that each entry is on one
   line. 

In logback, this looks like:

+-----+-------------------------------------------------------------------------------+
| 1   | <property name="defaultPattern" value="%nopexception%logger                   |
|     |                                                                               |
| 2   | \\t%date{yyyy-MM-dd'T'HH:mm:ss.SSSXXX,UTC}                                    |
|     |                                                                               |
| 3   | \\t%level                                                                     |
|     |                                                                               |
| 4   | \\t%replace(%replace(%message){'\\t','\\\\\\\\t'}){'\\n','\\\\\\\\n'}         |
|     |                                                                               |
| 5   | \\t%replace(%replace(%mdc){'\\t','\\\\\\\\t'}){'\\n','\\\\\\\\n'}             |
|     |                                                                               |
| 6   | \\t%replace(%replace(%rootException){'\\t','\\\\\\\\t'}){'\\n','\\\\\\\\n'}   |
|     |                                                                               |
| 7   | \\t%replace(%replace(%marker){'\\t','\\\\\\\\t'}){'\\n','\\\\\\\\n'}          |
|     |                                                                               |
| 8   | \\t%thread                                                                    |
|     |                                                                               |
| 9   | \\t%n"/>                                                                      |
+-----+-------------------------------------------------------------------------------+

The output of which, with MDCs, a Marker and a nested exception, with newlines added for readability looks like:

TODO: remove tab below

+------+-----------------------------------------------------------------------------------------------------------------------------+
| 1    | org.onap.example.component1.subcomponent1.LogbackTest                                                                       |
|      |                                                                                                                             |
| 2    | \\t2017-08-06T16:09:03.594Z                                                                                                 |
|      |                                                                                                                             |
| 3    | \\tERROR                                                                                                                    |
|      |                                                                                                                             |
| 4    | \\tHere's an error, that's usually bad                                                                                      |
|      |                                                                                                                             |
| 5    | \\tkey1=value1, key2=value2 with space, key5=value5"with"quotes, key3=value3\\nwith\\nnewlines, key4=value4\\twith\\ttabs   |
|      |                                                                                                                             |
| 6    | \\tjava.lang.RuntimeException: Here's Johnny                                                                                |
|      |                                                                                                                             |
| 7    | \\n\\tat org.onap.example.component1.subcomponent1.LogbackTest.main(LogbackTest.java:24)                                    |
|      |                                                                                                                             |
| 8    | \\nWrapped by: java.lang.RuntimeException: Little pigs, little pigs, let me come in                                         |
|      |                                                                                                                             |
| 9    | \\n\\tat org.onap.example.component1.subcomponent1.LogbackTest.main(LogbackTest.java:27)                                    |
|      |                                                                                                                             |
| 10   | \\tAMarker1                                                                                                                 |
|      |                                                                                                                             |
| 11   | \\tmain                                                                                                                     |
+------+-----------------------------------------------------------------------------------------------------------------------------+

Default Logstash indexing rules understand output in this format.

**********
XML Output
**********

For Log4j 1.X output, since escaping is not supported, the best
alternative is to emit logs in XML format. 

There may be other instances where XML (or JSON) output may be
desirable. Default indexing rules support 

Default Logstash indexing rules understand the XML output of \ `*Log4J's
XMLLayout* <https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/XMLLayout.html>`__.

Output Location
===============

Standardization of output locations makes logs easier to locate and ship
for indexing. 

Logfiles should default to beneath \ **/var/log**, and
beneath \ **/var/log/ONAP** in the case of core ONAP components:

+-----+-----------------------------------------------------+
| 1   | /var/log/ONAP/<component>[/<subcomponent>]/\*.log   |
+-----+-----------------------------------------------------+

Configuration
=============

Logging providers should be configured by file. Files should be at a
predictable, static location, so that they can be written by deployment
automation. Ideally this should be under \ **/etc/ONAP**, but compliance
is low.

Locations
=========

All logger provider configuration document locations namespaced by
component and (if applicable) subcomponent by default:

+-----+---------------------------------------------------------+
| 1   | /etc/onap/<component>[/<subcomponent>]/<provider>.xml   |
+-----+---------------------------------------------------------+

Where \ **<provider>.xml**, will typically be one of:

1. logback.xml

2. log4j.xml

3. log4j.properties

Reconfiguration
===============

Logger providers should reconfigure themselves automatically when their
configuration file is rewritten. All major providers should support
this. 

The default interval is 10s. 

Overrides
=========

The location of the configuration file MAY be overrideable, for example
by an environment variable, but this is left for individual components
to decide. 

Archetypes
============

Configuration archetypes can be found in the ONAP codebase. Choose
according to your provider, and whether you're logging via EELF. Efforts
to standardize them are underway, so the ones you should be looking for
are where pipe (\|) is used as a separator. (Previously it was "\|").

Retention
=========

Logfiles are often large. Logging providers allow retention policies to
be configured. 

Retention has to balance:

-  The need to index logs before they're removed. 

-  The need to retain logs for other (including regulatory) purposes. 

Defaults are subject to change. Currently they are:

1. Files <= 50MB before rollover. 

2. Files retain for 30 days. 

3. Total files capped at 10GB. 

In Logback configuration XML:

+------+-------------------------------------------------------------------------------------------------------------+
| 1    | <appender name="file" class="ch.qos.logback.core.rolling.RollingFileAppender">                              |
|      |                                                                                                             |
| 2    |     <file>${outputDirectory}/${outputFilename}.log</file>                                                   |
|      |                                                                                                             |
| 3    |     <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">                       |
|      |                                                                                                             |
| 4    |         <fileNamePattern>${outputDirectory}/${outputFilename}.%d{yyyy-MM-dd}.%i.log.zip</fileNamePattern>   |
|      |                                                                                                             |
| 5    |         <maxFileSize>50MB</maxFileSize>                                                                     |
|      |                                                                                                             |
| 6    |         <maxHistory>30</maxHistory>                                                                         |
|      |                                                                                                             |
| 7    |         <totalSizeCap>10GB</totalSizeCap>                                                                   |
|      |                                                                                                             |
| 8    |     </rollingPolicy>                                                                                        |
|      |                                                                                                             |
| 9    |     <encoder>                                                                                               |
|      |                                                                                                             |
| 10   |         <!-- ... -->                                                                                        |
|      |                                                                                                             |
| 11   |     </encoder>                                                                                              |
|      |                                                                                                             |
| 12   | </appender>                                                                                                 |
+------+-------------------------------------------------------------------------------------------------------------+

Types of EELF Logs
==================

EELF guidelines stipulate that an application should output log records
to four separate files:

1. audit

2. metric

3. error

4. debug

This applies only to EELF logging. Components which log directly to a
provider may choose to emit the same set of logs, but most do not. 

Audit Log
---------

An audit log is required for EELF-enabled components, and provides a
summary view of the processing of a (e.g., transaction) request within
an application. It captures activity requests that are received by an
ONAP component, and includes such information as the time the activity
is initiated, then it finishes, and the API that is invoked at the
component.

Audit log records are intended to capture the high level view of
activity within an ONAP component. Specifically, an API request handled
by an ONAP component is reflected in a single Audit log record that
captures the time the request was received, the time that processing was
completed, as well as other information about the API request (e.g., API
name, on whose behalf it was invoked, etc).

Metric Log
----------

A metric log is required for EELF-enabled components, and provides a
more detailed view into the processing of a transaction within an
application. It captures the beginning and ending of activities needed
to complete it. These can include calls to or interactions with other
ONAP or non-ONAP entities.

Suboperations invoked as part of the processing of the API request are
logged in the Metrics log. For example, when a call is made to another
ONAP component or external (i.e., non-ONAP) entity, a Metrics log record
captures that call. In such a case, the Metrics log record indicates
(among other things) the time the call is made, when it returns, the
entity that is called, and the API invoked on that entity. The Metrics
log record contain the same RequestID as the Audit log record so the two
can be correlated.

Note that a single request may result in multiple Audit log records at
an ONAP component and may result in multiple Metrics log records
generated by the component when multiple suboperations are required to
satisfy the API request captured in the Audit log record.

Error Log
---------

An error log is required for EELF-enabled components, and is intended to
capture info, warn, error and fatal conditions sensed (œexception
handled) by the software components.

Debug Log
---------

A debug log is optional for EELF-enabled components, and is intended to
capture whatever data may be needed to debug and correct abnormal
conditions of the application.

Engine.out
==========

Console logging may also be present, and is intended to capture
system/infrastructure records. That is stdout and stderr assigned to a
single œengine.out file in a directory configurable (e.g. as an
environment/shell variable) by operations personnel.

New ONAP Component Checklist
============================

By following a few simple rules:

-  Your component's output will be indexed automatically. 

-  Analytics will be able to trace invocation through your component.

Obligations fall into two categories:

1. Conventions regarding configuration, line format and output. 

2. Ensuring the propagation of contextual information. 

You must:

1. Choose a Logging provider and/or EELF. Decisions, decisions.

2. Create a configuration file based on an existing
   archetype. See \ `*Configuration* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-Configuration>`__.

3. Read your configuration file when your components initialize logging.

4. Write logs to a standard location so that they can be shipped by
   Filebeat for indexing. See \ `*Output
   Location* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-OutputLocation>`__.

5. Report transaction state:

   a. Retrieve, default and propagate \ **RequestID**. See \ `*MDC -
      RequestID* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-MDC-RequestID>`__.

   b. At each invocation of one ONAP component by another:

      i.   Initialize and propagate \ **InvocationID**. See \ `*MDC -
           Invocation
           ID* <https://wiki.onap.org/display/DW/ONAP+Application+Logging+Guidelines+v1.1#ONAPApplicationLoggingGuidelinesv1.1-MDC-InvocationID>`__.

      ii.  Report \ **INVOKE** and **SYNCHRONOUS** markers in caller. 

      iii. Report \ **ENTRY** and **EXIT** markers in recipient. 

6. Write useful logs!

 They are unordered.