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# Component Requirements: Docker
## Overview
Component developers are required to provide artifacts for the platform to be able to deploy your component including:
* [Component specification](component-specification/docker-specification)
* [Data formats](data-formats)
* [Auxiliary component specification](component-specification/docker-specification#auxiliary)
* [Docker image](#docker-on-the-platform)
In addition, components will have to be enhanced to be compliant with the DCAE platform in order to correctly be deployed and be managed. This page will discuss the changes which are grouped into the following categories:
* [Service registration](#service-registration)
* [Configuration management on the new platform](#configuration)
* [Operational concerns](#operational-concerns)
To help component developers to make and to test the changes needed to have components run on the platform, a command-line tool called [`dcae-cli`](dcae-cli/quickstart) is provided by the platform team.
## Service registration
Every [Docker component is registered](../architecture/service-discovery) with the platform's service discovery layer. Docker components are not expected to make the explicit make registration calls because that is done by through a platform 3rd party registration service. A couple things are needed from component developers in order for this registration to occur successfully:
1. Docker images must be created from a Dockerfile that has an [`EXPOSE`](https://docs.docker.com/engine/reference/builder/#/expose) instruction. This applies to components that listen on a port.
2. Component healthcheck details must be provided in the Docker auxiliary component specification
### Expose port
Components that listen on a specific port must explicitly declare in their Dockerfile that port using the `EXPOSE` instruction before building the image.
Warning! At the current time, you can not expose multiple ports in your Dockerfile or registration *will not work* correctly.
### Health check
Component developers are required to provide a way for the platform to periodically check the health of their running components. The platform uses Consul to perform these periodic calls. Consul provides different types of [check definitions](https://www.consul.io/docs/agent/checks.html). The details of the definition used by your component is to be provided through the [Docker auxiliary specification](component-specification/docker-specification#auxiliary).
## Configuration
The component's application configuration is generated from the submitted component specification into a JSON representation. The DCAE platform will provide the configuration JSON by making it available on a remote HTTP service. Components are required to pull their configuration JSON at application startup. The configuration JSON is stored under the components uniquely generated name which is provided by the environment variable `HOSTNAME`.
You can see more details on the generated application configuration [here](component-specification/docker-specification#generate-application-configuration).
### Config binding service
The config binding service is a platform HTTP service that is responsible for providing clients with a fully resolved configuration JSON at runtime. Components should make an HTTP GET on:
```
<config binding service hostname>:<port>/service_component/NAME
```
For Docker components, NAME should be set to `HOSTNAME`, which was provided as an ENV variable inside of your container.
The binding service integrates with the streams and services section of your component specification. For example, if you specify that you call a service:
```
"services": {
"calls": [{
"config_key": "vnf-db",
"request": {
"format": "dcae.vnf.meta",
"version": "1.0.0"
},
"response": {
"format": "dcae.vnf.kpi",
"version": "1.0.0"
}
}],
...
}
```
Then the config binding service will find all available IP addresses of services meeting your needs, and provide them to you under your `config_key`:
```
// your configuration
{
"vbf-db" : // see above
[IP:Port1, IP:Port2,…] // all of these meet your needs, choose one.
}
```
Regarding `<config binding service hostname>:<port>`, there is DNS work going on to make this resolvable in a convenient way inside of your container.
However, currently you will be given a name as an ENV variable, `CONFIG_BINDING_SERVICE`, and you will need to query Consul's service discovery to get
`<config binding service hostname>:<port>`.
### Policy Reconfiguration
*(Draft and subject to change)*
Components must provide a way to receive policy reconfiguration, that is, configuration parameters that have been updated via the Policy UI. The component developer provides a docker script (defined in the [Docker auxiliary specification](component-specification/docker-specification#policy-example)) that will be triggered when this occurs.
### DMaaP
Components can be publishers or subscribers to either message router topics or data router feeds. This is defined in the component specification under the `streams` section where you can specify whether your component is expected to subscribe or to publish to a [message router topic](component-specification/common-specification/#message-router) or to a [data router feed](component-specification/common-specification/#data-router). Given a composition with components that use DMaaP, the platform will provision the topic or feed and provide the necessary [connection details](dcae-cli/dmaap-connection-objects) at runtime for each DMaaP dependent component. These connection details will be provided through your application's [generated configuration](component-specification/generated-configuration).
In order to test DMaaP connections in onboarding, the developer (currently) must provision all test topics and feeds manually and provide the [dcae-cli with the connection details](dcae-cli/walkthrough/#dmaap-testing) when deploying your application.
## Docker on the platform
### Images
Docker images must be pushed to the environment specific Nexus repository. This requires tagging your build with the full name of you image which includes the Nexus repository name.
Use the Docker command-line to [tag](https://docs.docker.com/engine/reference/commandline/tag/) your Docker image where the *target image* must contain the registry host name and port.
For example, an application called laika has been tagged for an example Nexus registry:
```
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
YOUR_NEXUS_DOCKER_REGISTRY/laika 0.4.0 154cc382df61 7 weeks ago 710.5 MB
laika 0.4.0 154cc382df61 7 weeks ago 710.5 MB
```
Note, the Docker registry that is used may require a login to authenticate.
```
docker login YOUR_NEXUS_DOCKER_REGISTRY
```
Tag your image:
```
docker tag laika:0.4.0 YOUR_NEXUS_DOCKER_REGISTRY/laika:0.4.0
```
Or build and tag:
```
docker build -t YOUR_NEXUS_DOCKER_REGISTRY/laika:0.4.0 .
```
After tagging, upload your image to the remote registry using the Docker [push command](https://docs.docker.com/engine/reference/commandline/push/). Note that the registry may require a login. Use the Docker [login command](https://docs.docker.com/engine/reference/commandline/login/) before pushing in that case.
```
docker push YOUR_NEXUS_DOCKER_REGISTRY/laika:0.4.0
```
*NOTE* Replace `laika` with your application's name. Replace the `0.4.0` version with your application's version.
### Ports
On the DCAE platform, Docker components are run with the `--publish-all` or `-P` argument. This means the Docker container for your component will be listening on a random port and that random port will be mapped to the port [you exposed](#service-registration).
### Envs
The platform provides a set of environment variables into each Docker container:
Name | Type | Description
---- | ---- | -----------
`HOSTNAME` | string | Unique name of the component instance that is generated
`CONSUL_HOST` | string | Hostname of the platform's Consul instance
`CONFIG_BINDING_SERVICE` | string | Hostname of the platform's config binding service instance
`DOCKER_HOST` | string | Host of the target platform Docker host to run the container on
## Operational concerns
### Logging
Currently the platform uses the default `json-file` logging driver for Docker. For onboarding testing, component developers can access their logs from their Docker containers either by running their component using the `--attached` flag or by using the `docker logs` command. The requirement is that applications must write to stdout and/or stderr.
To use the `docker logs` command for your deployed running Docker container,
1. You must have Docker installed on your local machine
2. Have the generated name of your component. This is generated for you when you execute `dcae_cli component dev` or `dcae_cli component run`.
3. Find the target Docker host using the `dcae_cli profiles show` command:
```
$ dcae_cli profiles show YOUR_PROFILE_NAME
{
...
"docker_host": "YOUR_DOCKER_HOST:2376"
}
```
4. Set your Docker client to point to the target Docker host:
```
$ export DOCKER_HOST="tcp://YOUR_DOCKER_HOST:2376"
```
5. Use the `docker logs` command:
```
$ docker logs <generated component name>
```
|
