Introduce Driver Capabilities

This spec introduces inspectable (via Ironic API) capabilities for Ironic drivers.

https://blueprints.launchpad.net/ironic/+spec/driver-capabilities

Problem description

Capabilities are required for at least these use cases:

  • Scheduling on a node with a proper driver.

    E.g. with time we start implementing variants of deployment that are not supported by all drivers, including:

    • Whole-disk vs partition deployment [1].

    • Using configdrive for deployment [2].

    • Using ephemeral partitions.

    We need to take all these differences into account when scheduling. Failure to do so will lead to errors on the late stage of deployment or even (as with whole-disk) to the wrong deployment.

    Ironic should be able to aggregate driver capabilities into node capabilities to expose them to the scheduler. (Not addressed by this spec.)

  • Examining driver features.

    As we are introducing more vendor-specific things, we need some way to find out, if one is supported by a given driver. Driver capabilities would enable 3rd-party tools to inspect support of particular feature by particular driver.

Proposed change

  • Introduce get_capabilities() call to all driver interfaces, return value being set of strings.

  • Introduce get_capabilities() call to BaseDriver, defaulting to union of capabilities of all interfaces.

  • Publish capabilities as /v1/drivers/{name}/capabilities REST endpoint.

With the above changes, a developer could use the Ironic API to go through the list of drivers and inspect their capabilities.

Alternatives

  • Obviously the best solution would be to have all drivers implement the same set of capabilities. Unfortunately, it’s not realistic. E.g. some drivers (like IPMI) are more generic than the other (like ILO and DRAC), but we don’t want to artificialy limit what more specific drivers can expose.

Data model impact

None. For now we expect driver capabilities to be a hardcoded constant.

REST API impact

  • /v1/drivers/{name}/capabilities

    • Get driver capabilities.

    • Method type GET.

    • Normal http response code(s): 200

    • Expected error http response code(s)

      • 404 - driver not found.

    • Parameter: name - driver name

    • Body: None

    • Response: JSON list of strings.

  • A corresponding change in the client library and CLI is necessary, e.g.

    $ ironic driver-get-capabilities pxe_ipmitool

RPC API impact

  • New synchronous RPC method get_driver_capabilities, taking driver_name, returning list of capabilities.

Driver API impact

  • New method get_capabilities added to all interfaces, defaulting to returning an empty set.

  • New method get_capabilities added to the BaseDriver, defaulting to returning a union of get_capabilities results for all interfaces.

Change is backward-compatible.

Nova driver impact

None for now. This spec is a starting point to implement hardware capabilities for nodes [3], which will affect Nova driver.

Security impact

None

Other end user impact

  • New CLI command: ironic driver-get-capabilities <driver name>

Scalability impact

None

Performance Impact

None

Other deployer impact

None

Developer impact

  • Driver developers can override get_capabilities to provide information about additional capabilities.

Implementation

Assignee(s)

Primary assignee:

None

Work Items

  • Add get_capabilities to all interfaces.

  • Add get_capabilities to the BaseDriver.

  • Add get_driver_capabilities to the RPC API.

  • Add new REST API.

  • Research whether to add capabilities to existing drivers.

Dependencies

None

Testing

Unit tests

Upgrades and Backwards Compatibility

No upgrade impact

Documentation Impact

  • New API should be documented.

  • Driver documentation should mention the new method.

References