OpenAPI Schemas

https://blueprints.launchpad.net/nova/+spec/openapi

We would like to start documenting our APIs in an industry-standard, machine-readable manner. Doing so opens up many opportunities for both OpenStack developer and OpenStack users alike, notably the ability to both auto-generate and auto-validate both client tooling and documentation alike. Of the many API description languages available, OpenAPI (fka “Swagger”) appears to be the one with both the largest developer mindshare and the one that would be the best fit for OpenStack due to the existing tooling used in many OpenStack services, thus we would opt to use this format.

Problem description

The history of API description languages has been mainly a history of half-baked ideas, unnecessary complication, and in general lots of failure. This history has been reflected in OpenStack’s own history of attempting to document APIs, starting with our early use of WADL through to our experiments with Swagger 2.0 and RAML, leading to today’s use of our custom os_api_ref project, built on reStructuredText and Sphinx.

It is only in recent years that things have started to stabilise somewhat, with the development of widely used API description languages like OpenAPI, RAML and API Blueprint, as well as supporting SaaS tools such as Postman and Apigee. OpenAPI in particular has seen broad adoption across multiple sectors, with sites as varied as CloudFlare and GitHub providing OpenAPI schemas for their APIs. OpenAPI has evolved significantly in recent years and now supports a wide variety of API patterns including things like webhooks. Even more beneficial for OpenStack, OpenAPI 3.1 is a full superset of JSON Schema meaning we have the ability to re-use much of the validation we already have.

Use Cases

As an end user, I would like to have access to machine-readable, fully validated documentation for the APIs I will be interacting with.

As an end user, I want statically viewable documentation hosted as part of the existing docs site without requiring a running instance of Nova.

As an SDK/client developer, I would like to be able to auto-generate bindings and clients, promoting consistency and minimising the amount of manual work needed to develop and maintain these.

As a Nova developer, I would like to have a verified API specification that I can use should I need to replace the web framework/libraries we use in the event they are no longer maintained.

Proposed change

This effort can be broken into a number of distinct steps:

• Add a new decorator for removed APIs and actions

  We have a number of APIs and actions that no longer have backing code and return HTTP 410 (Gone) or HTTP 400 (Bad Request), respectively. We will not add schemas for these in the initial attempt at this so we need some mechanism to indicate this. We will add a new removed decorator that will highlight these removed APIs and indicate the version they were removed in and the reason for their removal. We can later use this as a heuristic in our tests to skip schema checks for these methods.

• Add missing request body and query string schemas

  There is already good coverage of both request bodies and query string parameters but it is not complete. A list of incomplete schemas is given at the end of this section. The additional schemas will merely validate what is already allowed, which will mean extensive use of "additionalProperties": true or empty schemas. Put another way, an API that currently ignores unexpected request body fields or query string parameters will continue to ignore them. We may wish to make these stricter, as we did for most APIs in microversion 2.75, but that is a separate issue that should be addressed separately.

  Once these specs are added, tests will be added to ensure all non-deprecated and non-removed API resources have appropriate schemas.

• Add response body schemas

  These will be sourced from existing OpenAPI schemas, currently published at github.com/gtema/openstack-openapi, from Tempest’s API schemas, and where necessary from new schemas auto-generated from JSON response bodies generated in tests and manually modified handle things like enum values.

  Once these are added, tests will be added to ensure all non-deprecated and non-removed API resources have appropriate response body schemas. In addition, we will add a new configuration option that will control how we do verification at the API layer, [api] response_validation. This will be an enum value with three options:

  error

  Raise a HTTP 500 (Server Error) in the event that an API returns an “invalid” response.

  This will be the default in CI i.e. for our unit, functional and integration tests. This should not be used in production. The help text of the option will indicate this and we will set the advanced option.

  warn

  Log a warning about an “invalid” response, prompting operations to file a bug report against Nova.

  This will be initial (and likely forever) default in production.

  ignore

  Disable API response body validation entirely. This is an escape hatch in case we mess up.

Note

The development of tooling required to gather these JSON Schema schemas and generate an OpenAPI schema will not be developed inside Nova and is therefore not covered by this spec. Nova will merely consume the resulting tooling for use in documentation. It is intended that the same tool will be usable across any OpenStack project that uses the same web frameworks (in Nova’s case, WebOb + Routes).

Note

The impact of middleware that modifies either the request or response will not be accounted for in this change. This is because these are configurable and they cannot be guaranteed to exist in a given deployment. Examples include the sizelimit middleware from oslo.middlware and the auth_token middleware from keystonemiddleware.

Alternatives

• Use a different tool

  We could use a different tool than OpenAPI to publish our specs. In a manner of speaking we already do this - albeit not in a machine-readable manner - through our use of os-api-ref.

  This idea has been rejected because OpenAPI is clearly the best tool for the It is the most widely used API description language available today and aligns well with our existing use of JSON Schema for API validation. While it does not support OpenStack’s microversion API design pattern out-of-the-box, previous experiments have demonstrated that it is extensible enough to add this.

• Maintain these specs out-of-tree

  We could use a separate repo to store and maintain specs for Nova and the other OpenStack services.

  This idea has been rejected because it prevents us testing the specs on each commit to Nova and means work that could be spread across multiple teams is instead focused on one small team. It will result in more bugs and a lag between changes to the Nova API and changes to the out-of-tree specs. It will result in duplication of effort across Nova, Tempest, and the specs projects.

• Publish the spec via an API resource rather than in our docs

  We could publish the spec via a new, unversioned API endpoint such as /spec. A GET request to this would return the full spec, either statically generated at deployment time or dynamically generated (and then cached) at runtime.

  This is rejected because it brings limited advantages and multiple disadvantages. Nova’s API is designed to be backwards-compatible and non-extensible. As such, a user with the latest version of the spec should be able to use it to communicate with any OpenStack deployment running a version of Nova that supports microversions. It is also expected that the “master” version of the spec will continuously improve as things are tightened up, documentation is improved, and bugs or mistakes are corrected. We want consumers of the spec to see these changes immediately rather than wait for their deployment to be updated. Finally, OpenStack’s previous forays into discoverable APIs, such as Keystone’s use of JSONHome or Glance’s attempts to publish resource schemas, have seen limited take-up outside of the projects themselves. Taken together, this all suggests there is no reason or advantage to publishing deployment-specific specs and users would be better served by fetching the latest version of the spec from the api-ref documentation published on docs.openstack.org (which, one should note, is itself intentionally unversioned).

Data model impact

None.

REST API impact

There will be no direct REST API impact. Users will see HTTP 500 error if they set [api] response_validation = error and encounter an invalid response, however, we will not encourage use of this option in production and will instead focus on validating this ourselves in CI.

We may wish to address issues that are uncovered as we add schemas, but this work is considered secondary to this effort and can be tackled separately.

Security impact

None.

Notifications impact

None.

Other end user impact

This should be very beneficial for users who are interested in developing client and bindings for OpenStack. In particular, this should (after an initial effort in code generation) reduce the workload of the SDK team as well as teams outside of OpenStack that work on client tooling such as the Gophercloud team.

Performance Impact

There will be a minimal impact on API performance when validation is enabled as we will now verify both requests and responses for all API resources. Given our existing extensive use of JSON Schema for API validation, it is expected that this should not be a significant issue.

Other deployer impact

As noted previously, there will be one new config option, [api] response_validation. Operators may see increased warnings in their logs due to incomplete schemas, but most if not all of these issues should be ironed out by our CI coverage.

Developer impact

Developers working on the API microversions will now be encouraged to provide JSON Schema schemas for both requests and responses.

Upgrade impact

None.

Implementation

Assignee(s)

Primary assignee:

stephenfinucane

Other contributors:

gtema

Feature Liaison

None.

Work Items

• Add missing request body schemas

• Add tests to validate existence of request body schemas

• Add missing query string schemas

• Add tests to validate existence of query string schemas

• Add response body schemas

• Add decorator to validate response body schemas against response

• Add tests to validate existence of response body schemas

Dependencies

The actual generation of an OpenAPI documentation will be achieved via a separate tool. It is not yet determined if this tool will live inside an existing project, such as os_api_ref or openstacksdk, or inside a wholly new project. In any case, it is envisaged that this tool will handle OpenStack-specific nuances like microversions that don’t map 1:1 to OpenAPI concepts in a consistent and documented fashion.

Testing

Unit tests will ensure that schemas eventually exist for request bodies, query strings, and response bodies.

Unit, functional and integration tests will all work together to ensure that response body schemas match real responses by setting [api] response_validation to error.

Documentation Impact

Initially there should be no impact as we will continue to use os_api_ref as-is for our api-ref docs. Eventually we will replace or extend this extension to generate documentation from our OpenAPI schema.

References

APIs missing schemas

These are the APIs that are currently (as of 2024-04-11, commit 1bca24aeb) missing API request body schemas and query string schemas.

Missing request body schemas

• AdminActionsController._inject_network_info

• AdminActionsController._reset_network

• AgentController.create

• AgentController.update

• BareMetalNodeController._add_interface

• BareMetalNodeController._remove_interface

• BareMetalNodeController.create

• CellsController.create

• CellsController.sync_instances

• CellsController.update

• CertificatesController.create

• CloudpipeController.create

• CloudpipeController.update

• ConsolesController.create

• DeferredDeleteController._force_delete

• DeferredDeleteController._restore

• FixedIPController.reserve

• FixedIPController.unreserve

• FloatingIPBulkController.create

• FloatingIPBulkController.update

• FloatingIPController.create

• FloatingIPBulkController.create

• FloatingIPBulkController.update

• FloatingIPController.create

• FloatingIPDNSDomainController.update

• FloatingIPDNSEntryController.update

• LockServerController._unlock

• NetworkAssociateActionController._associate_host

• NetworkAssociateActionController._disassociate_host_only

• NetworkAssociateActionController._disassociate_project_only

• NetworkController._disassociate_host_and_project

• NetworkController.add

• NetworkController.create

• PauseServerController._pause

• PauseServerController._unpause

• RemoteConsolesController.get_rdp_console

• RescueController._unrescue

• SecurityGroupActionController._addSecurityGroup

• SecurityGroupActionController._removeSecurityGroup

• SecurityGroupController.create

• SecurityGroupController.update

• SecurityGroupDefaultRulesController.create

• SecurityGroupRulesController.create

• ServersController._action_confirm_resize

• ServersController._action_revert_resize

• ServersController._start_server

• ServersController._stop_server

• ShelveController._shelve

• ShelveController._shelve_offload

• SuspendServerController._resume

• SuspendServerController._suspend

• TenantNetworkController.create

Missing request query string schemas

• AgentController.index

• AggregateController.index

• AggregateController.show

• AvailabilityZoneController.detail

• AvailabilityZoneController.index

• BareMetalNodeController.index

• BareMetalNodeController.show

• CellsController.capacities

• CellsController.detail

• CellsController.index

• CellsController.info

• CellsController.show

• CertificatesController.show

• CloudpipeController.index

• ConsoleAuthTokensController.show

• ConsolesController.index

• ConsolesController.show

• ExtensionInfoController.index

• ExtensionInfoController.show

• FixedIPController.show

• FlavorAccessController.index

• FlavorExtraSpecsController.index

• FlavorExtraSpecsController.show

• FlavorsController.show

• FloatingIPBulkController.index

• FloatingIPBulkController.show

• FloatingIPController.index

• FloatingIPController.show

• FloatingIPDNSDomainController.index

• FloatingIPDNSEntryController.show

• FloatingIPPoolsController.index

• FpingController.index

• FpingController.show

• HostController.reboot

• HostController.show

• HostController.shutdown

• HostController.startup

• HypervisorsController.detail

• HypervisorsController.index

• HypervisorsController.search

• HypervisorsController.servers

• HypervisorsController.show

• HypervisorsController.statistics

• HypervisorsController.uptime

• IPsController.index

• IPsController.show

• ImageMetadataController.index

• ImageMetadataController.show

• ImagesController.detail

• ImagesController.index

• ImagesController.show

• InstanceActionsController.index

• InstanceActionsController.show

• InstanceUsageAuditLogController.index

• InstanceUsageAuditLogController.show

• InterfaceAttachmentController.index

• InterfaceAttachmentController.show

• NetworkController.index

• NetworkController.show

• QuotaClassSetsController.show

• QuotaSetsController.defaults

• QuotaSetsController.detail

• QuotaSetsController.show

• SecurityGroupController.show

• SecurityGroupDefaultRulesController.index

• SecurityGroupDefaultRulesController.show

• ServerDiagnosticsController.index

• ServerGroupController.show

• ServerMetadataController.index

• ServerMetadataController.show

• ServerMigrationsController.index

• ServerMigrationsController.show

• ServerPasswordController.index

• ServerSecurityGroupController.index

• ServerTagsController.index

• ServerTagsController.show

• ServerTopologyController.index

• ServerVirtualInterfaceController.index

• ServersController.show

• SnapshotController.show

• TenantNetworkController.index

• TenantNetworkController.show

• VersionsController.show

• VolumeAttachmentController.show

• VolumeController.show

Note

We should emphasise that many - but not all - of the aforementioned APIs are either deprecated or removed. We may wish not to add schemas for these, though by doing so we will lose the ability to generate documentation or clients for these APIs from the OpenAPI spec.

History

Revisions

Release Name	Description
2024.2 Dalmatian	Introduced