placement charm: OpenStack upgrade to Train

As of OpenStack Train, the Placement API is managed by the new placement charm and is no longer managed by the nova-cloud-controller charm. The upgrade to Train therefore involves some coordination to transition to the new API endpoints.

Prior to upgrading nova-cloud-controller services to Train, the placement charm must be deployed for Train and related to the Stein-based nova-cloud-controller application. It is important that the nova-cloud-controller unit leader is paused while the API transition occurs (paused prior to adding relations for the placement charm) as the placement charm will migrate existing placement tables from the nova_api database to a new placement database. Once the new placement endpoints are registered, nova-cloud-controller can be resumed.

Here are example commands for the process just described:

juju deploy --series bionic --config openstack-origin=cloud:bionic-train placement
juju run-action --wait nova-cloud-controller/leader pause
juju add-relation placement percona-cluster
juju add-relation placement keystone
juju add-relation placement nova-cloud-controller

List endpoints and ensure placement endpoints are now listening on the new placement IP address. Follow this up by resuming nova-cloud-controller:

openstack endpoint list
juju run-action --wait nova-cloud-controller/leader resume

Finally, upgrade the nova-cloud-controller services. Below all units are upgraded simultaneously but see the paused-single-unit service upgrade method for a more controlled approach:

juju config nova-cloud-controller openstack-origin=cloud:bionic-train