Enable cold migration with target host

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

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

Problem description

I have a customized HA plugin which automatically performs migrations under certain conditions, and the HA plugin is able to intelligently pick up destinations, but only live migrations support specifying destinations.

At the moment cold migration do not support migrate a VM instance with target host, this blueprint want to add this feature to nova so that above scenario can be satisified.

It also make cold migration consistent with live-migrate operations as live migration support migration with and w/o target host.

Proposed change

Modify the current resize_instance flow to let the api can specify the target host for cold migration.

Alternatives

None

Data model impact

None

REST API impact

• For V2 API, a new extension will be added as: alias: os-extended-admin-actions name: ExtendedAdminActions namespace: http://docs.openstack.org/compute/ext/extended_admin_actions/api/v1.1

  When the new extension “os-extended-admin-actions” is loaded, the api of _migrate() wil support cold migration with target host.

• For a later microversion of v2.1 API, no new extension needed, the existing cold migration API will be updated to support this.

• URL: existed admin actions extension as:

  • /v2/{tenant_id}/servers/actions:

  • /v2.1/servers/actions:

  JSON request body:

  {
      "migrate":
      {
          "host": "fake_host"
      }
  }
  

Security impact

None

Notifications impact

None

Other end user impact

python-novaclient will be modified to have target_host argument as optional.

The user can trigger this feature by: nova migrate my_server target_host

Performance Impact

None

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

jay-lau-513

Work Items

• Add logic to select target host for cold migration

• Add API v2/v2.1

• Set target host optional on nova-client

Dependencies

None

Testing

Add unit test in nova to cover the case of cold migration with target host, also we probably need to think about adding functionnal tests in tempest.

Documentation Impact

• Api Docs to reflect that target host field is optional.

• Client docs ( due to optional arg)

• Admin User Guide on cold migration topic.

References

None