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diff --git a/docs/specs/elastic_api_exposure.rst b/docs/specs/elastic_api_exposure.rst new file mode 100644 index 0000000..4cea241 --- /dev/null +++ b/docs/specs/elastic_api_exposure.rst @@ -0,0 +1,240 @@ +.. + This work is licensed under a Creative Commons Attribution 4.0 + International License. + +==================================== +Elastic API exposure for Multi Cloud +==================================== + +This spec is to provide a framework for Multi-Cloud to expose API. + +Problem Description +=================== + +Multi-Cloud provides VIM API for other projects in ONAP. API will vary for +different projects. However, Multi-Cloud exposes its API by static code. +Current way of API exposing produces code duplications. + +#. When a client creates a resource through Multi-Cloud, Multi-Cloud needs +to convert the API request to back-end OpenStack API request and send to +OpenStack. When a client requests a resource through Multi-Cloud, Multi-Cloud +needs to retrieve OpenStack resource, converts to its API and reply to client. +Even though the two conversion are the same thing with different directions, +there are 2 sets of code for it. + +#. Most of Multi-Cloud API shares same logic. But the code of this same logic +are duplicated for every API. + +Given the fact mentioned above, current code amount of Multi-Cloud are larger +than it should be. It makes code maintaining be time-consuming and error-prone. + +Besides, the swagger files that describe API of Multi-Cloud are maintained +manually. It is thousands lines of code and hard for developers to maintain. + +Proposed Change +=============== + +This spec proposes using YAML files to describe Multi-Cloud API. A framework +will also be provided. When Multi-Cloud services start up, the framework will +read YAML files, parse them and generate API accordingly. Multi-Cloud can +dynamically expose API in this way without changing its Python code. And +developers only need to maintain YAML files that describe Multi-Cloud API. +The YAML files are expected to be less amount than current way of API exposing, +because it only contains metadata of Multi-Cloud API. + +Using the proposal in this spec, metadata of API are defined in YAML files and +logic of API handling are concentrated in the framework mentioned above. So +that the code duplication can be eliminated. + +To narrow down the scope of this spec, none of current Multi-Cloud API will be +changed. This spec will ONLY focus on migrating Multi-Cloud API from current +way to the proposed framework in this spec. However, migrating all API to the +proposed framework is out of the scope of this spec. A set of API for one +specific use case, for example VoLTE, will be migrated to proposed framework. +Migrating all API can be implemented in other workitem(s) in future. + +To narrow down the scope of this spec, a full, normative definition of API and +resources will not be considered. Only partial API will be considered. But it +can be implemented in other workitem(s) in future. + +To narrow down the scope of this spec, only the functionality that Multi-Cloud +has now will be considered and extension support will not be considered in this +spec. But it can be implemented in other workitem(s) in future. + +It should be noted that, though this spec focuses on how to convert northbound +and southboud API, it doesn't prevent tieing northbound API of MultCloud with +other functionalities. In setion `Definition of API`, an example of API +definition has been given, developer can add specific code/module path as a +attribute(like `handler`) under `path`, instead of defining `vim_path`. By +doing that, developer can tie the northbound API with specific code/module, +and expose northbound API with any functionality. This spec just shows +the capability of doing this by using the elastic API exposure framework, the +implementation for now will still focus on the northbound and southboud API +conversion. + +It should be noted that there is a prior art in OpenStack "Gluon" [1]_ project +which provides a model-driven framework to generate APIs based on model definitions +in YAML. A full, normative definition and extension mechanism of "API Specification" +[2]_ is available in Gluon. Although our current work has limited scope, for those +who are interested in full normative definition and extension mechanism in our future +work, please refer to those references in "Gluon" [1]_ project and its "API +Specifications" [2]_. + +.. [1] https://wiki.openstack.org/wiki/Gluon +.. [2] https://github.com/openstack/gluon/blob/master/doc/source/devref/gluon_api_spec.inc + +Since the API are defined by YAML files, swagger files can also be generated +from YAML files and exist without manually maintaining. The framework will cover +the conversion from YAML file to swagger files. + +To keep backward compatibility, the proposal in this spec will be bound to [MULTICLOUD-150]_. +This means that the proposal is only usable when evenlet with pecan is +enabled. So that uses don't care about this feature will not be affected. + +.. [MULTICLOUD-150] https://jira.onap.org/browse/MULTICLOUD-150 + + +Definition of API +----------------- + +Take the API of `host` as example. The API will be defined as follow. URLs of +the API are defined under `paths`. There are several attributes for the API. The +number of kinds of attributes is not constrained to following example, other +attributes can be added if needed. + +:: + + paths: + /{vimid}/{tenantid}/hosts/{hostid}: + parameters: + - type: string + format: uuid + name: vimid + - type: string + format: uuid + name: tenantid + - type: string + format: uuid + name: hostid + get: + responses: + success_code: 200 + description: content of host + schema: host + vim_path: {nova_endpoint}/os-hypervisors + +parameters +~~~~~~~~~~ + +`parameters` are the variables in the URL. It can be extracted from URL and then +used in data retrieving and manipulating. + +`parameters` are discriminated by `name`, and validated by `type` and `format`. + +post, put, get, delete +~~~~~~~~~~~~~~~~~~~~~~ + +These attributes represents the supported HTTP method. In above example, only +`get` method is defined. When client sends other HTTP method to the URL, a 404 +response will be returned. + +`responses` defines the response of the request. `success_code` is the HTTP code +in the response. `description` is an optional parameter. It describes the response. +`schema` points to the RESTful resource that will be in the response body. In +above example, the RESTful resource is `host`. It should be found in the RESTful +resource definition section. + +vim_path +~~~~~~~~ + +`vim_path` defines the relative URL path of the southbound VIM. Multi-Cloud will +use this path to retrieve data from VIM. + +Definition of RESTful resource +------------------------------ + +Take the resource `host` as example. The resource will be defined as follow. +Resources are defined under `definitions`. The are several attributes for the +resource. The number of kinds of attributes is not constrained to following +example, other attributes can be added if needed. + +:: + + definitions: + host: + vim_resource: hypervisor + properties: + name: + type: string + required: true + source: hypervisor.name + cpu: + type: integer + minimal: 1 + source: hypervisor.vcpus + action: copy + required: true + disk_gb: + type: integer + minimal: 0 + source: hypervisor.local_disk_size + required: true + memory_mb: + type: integer + minimal: 0 + source: hypervisor.memory_size + required: true + +vim_resource +~~~~~~~~~~~~ + +`vim_resource` points to the resource that comes from southbound VIM. Multi-Cloud +will use the resource to build its own resource. + +properties +~~~~~~~~~~ + +`properties` defines the properties of the resource. Each property has a name +and several attributes. The number of kinds of attributes is not constrained +to the example, other attributes can be added if needed. + +`type` of property means the type of current property. It can be some simple data, +like string or integer. It can also be some composite data like, object or array. + +`required` of property means if this property is required for the resource. If it +is required, missing this property will cause request failure. Default value of +`required` is false. + +`source` of property means that current property will be built from it. It is +usually a property from `vim_resource`. By default, it will be the same property +in `vim_resource`. + +`action` of property means that current property will be build by using this action. +By default, it will be `copy`, which means the data from property of VIM resource +is copied to property of Multi-Cloud resource. Other actions can be defined for +different scenarios. + +`minimal` is one of the constraint of the property. It means the minimal possible +value of the property. If value of the property is less than minimal value. The +request will fail. + +Swagger File generation +----------------------- + +Multi-Cloud is using Swagger file to describe its API. It is maintained manually. +Since this spec proposes to use YAML file to generate Multi-Cloud's API, Swagger +file can also be generated from YAML file. The API generating framework will also +generate Swagger file. + +Implementation +============== + +Work Items +---------- + +#. Add YAML parser for API and resource. +#. Add REST client to call southbound VIM API. +#. Add validator for resource. +#. Add action for resouce. +#. Add Swagger file generator. +#. Migrate /{vimid}/{tenantid}/hosts/{hostid} as an example. |