Enable cold migration with target host - Queens

https://blueprints.launchpad.net/nova/+spec/cold-migration-with-target-queens

The aim of this feature is to let operators cold migrate instances with target host manually.

Problem description

A target host can be specified on the live migration operation. But a target host cannot be specified on the cold migration operation. It is inconsistent with the live migration operation, and both of these operations have similar circumstances when the host needs to be specified.

Use Cases

It is same as the live migration use case. Sometimes an operator or a script decides which host is the best suited to accept a cold migration and then wants to perform it. Consistency with a live migration case should be ensured.

Proposed change

Modify the API and the current resize_instance flow to be able to specify the target host for cold migration.

Add the function to check whether a destination host is in accordance with scheduler rules or not in cold migration as a default behaviour. Specifically to say, add setting ‘requested_destination’ of the RequestSpec object in nova/compute/api.py. The field has already been supported in the scheduler, so it just needs to be filled in.

Alternatives

None

Data model impact

None

REST API impact

• URL: POST /v2.1/servers/{server_id}/action

  JSON request body:

  {
      "migrate": {
          "host": "target-host"
      }
  }
  

The ‘host’ parameter to specify a target host is optional. Microversion is bumped up.

Security impact

None

Notifications impact

None

Other end user impact

python-novaclient will be modified to have a target host argument as optional.

nova migrate <server> [<host>]

Performance Impact

None

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

natsume-takashi

Work Items

• Add logic to specify target host for cold migration

• Add processing checking destination host in the cold migration

• Disable retries of the scheduling when the target host is specified

• Add API with bumping a new microversion

• Add nova functional tests

• Add tempest tests

Dependencies

None

Testing

Add the following tests.

• Unit tests

• Functional tests

• Tempest tests

Documentation Impact

• API Reference

• CLI Reference

• Admin User Guide on cold migration topic.

References

Mailing list discussion about why force flag is not added as part of this proposal: http://lists.openstack.org/pipermail/openstack-dev/2017-August/121654.html

History

The blueprint has been approved for Ocata as ‘cold-migration-with-target-ocata’ and for Pike as ‘cold-migration-with-target-pike’. It is renamed to ‘cold-migration-with-target-queens’ now. But the ‘force’ parameter to bypass the scheduler check is removed in the spec.

Revisions

Release Name	Description
Ocata	Approved
Pike	Reapproved
Queens	Reproposed