List requested Availability Zones

https://blueprints.launchpad.net/nova/+spec/list-requested-az

Currently server show and server list –long output, displays the current AZ of the instance. That is, the AZ to which the host of the instance belongs. There is no way to tell from this information that whether the instance create request included an AZ or not.

This implementation enables users to validate that their request for Availability Zone was correctly processed and satisfied, by returning back information, not only about current placement of the instance, but also original request.

Problem description

As of today, the server show and server list –long output, displays the current AZ of the instance. That is, the AZ to which the host of the instance belongs. There is no way to tell from this information that whether the instance created request included an AZ or not.

Also when cross_az_attach option is False and booting an instance from volume, the instance can be pinned to AZ and in that case, instance will be scheduled on host belonging to pinned AZ.

Also when default_schedule_zone config option set to specific AZ, in that case, instance would be pinned to that specific AZ, and instance will be scheduled on host belonging to pinned AZ.

Use Cases

  • As an operator, I want to know if the instance create request asked for an AZ expliclity or not. And whether the requested AZ and current AZ are both same or different.

Proposed change

The instances table from nova cell database does not have requested availability zone information. The same can be get from request_specs table in nova_api database.

For server show output, use the existing get_by_instance_uuid method from RequestSpec object and display it in the output.

For server list –long output, implement a method get_by_instance_uuids for RequestSpec object, which takes list of instance uuids of instances which will be shown in the listed output and return a list of RequestSpec objects of those instances.

Alternatives

As an alternative, we could add the requested availability zone information in instances table and when doing server list –long or server show use the data from instances table only and display to users, but it would duplicate the data in request_specs table as well as in instances table.

Data model impact

For implementation, we need to add a method get_by_instance_uuids to the RequestSpec object, which takes list of instance uuids as input and returns list of RequestSpec objects of those instances.

REST API impact

This change will be done with a new microversion bump.

Below are the two APIs that will be changed.

GET /servers/{server_id}

  • server show api response will include availability zone requested during server creation.

    {
  "server":
      {
          ...
          "pinned_availability_zone": None
          ...
      }
}

GET /servers/detail

  • server list –long api response will include availability zone requested during server creation.

    {
  "servers": [
      {
          ...
          "pinned_availability_zone": None
          ...
      }
      {
          ...
          "pinned_availability_zone": None
          ...
      }
  ]
}

Security impact

None

Notifications impact

None

Other end user impact

Performance Impact

There will be minor performance impact when user calls server list –long because we will be adding another database call to get list of request_specs of instances.

Other deployer impact

None

Developer impact

None

Upgrade impact

None

Implementation

Assignee(s)

Primary assignee:

ratailor

Feature Liaison

Feature liaison:

ratailor

Work Items

  • Implement API changes

  • Add tests

Dependencies

  • openstackclient and openstacksdk needs to be updated to implement this change.

Testing

  • Add unit tests

  • Add functional tests (API samples)

Documentation Impact

The api-ref will be updated to reflect the changes.

References

None

History

Revisions

Release Name

Description

2024.1 Caracal

Introduced