[Bug 1588462] Related fix proposed to charm-nova-cloud-controller (master)

[OpenStack Infra]

Related fix proposed to branch: master
Review: https://review.openstack.org/329219

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https://bugs.launchpad.net/bugs/1588462

Title:
  Status set race condition in OpenStack charms with optional relations

Status in ceph-radosgw package in Juju Charms Collection:
  New
Status in cinder package in Juju Charms Collection:
  New
Status in glance package in Juju Charms Collection:
  Fix Committed
Status in keystone package in Juju Charms Collection:
  New
Status in neutron-api package in Juju Charms Collection:
  New
Status in neutron-gateway package in Juju Charms Collection:
  New
Status in nova-cloud-controller package in Juju Charms Collection:
  New

Bug description:
  In charms that call assess_status() on every hook execution and that have
  optional relations there are two places where status_set() is called in
  set_os_workload_status() and make_assess_status_func()'s _assess_status_func()
  leading to a race condition in which a status may be overwritten.

  For charms like nova-cloud-controller where strangely we call
  set_os_workload_status() on each hook execution instead of assess_status() we
  only see this during pause and resume actions which do call assess_status().

  Regardless of __if__ you hit the race condition you can see the problem simply
  using print statements and an update-status hook run:
  'STATUS SET IN set_os_workload_status', 'active', 'Unit is ready'
  'STATUS SET IN _assess_status_func()', 'active', 'Unit is ready'

  If the first happened to be different the second would clobber it.

  In the set_os_workload_status() stack a comparison is made against the current
  status before setting status. The assess_status() stack needs to do the same
  possibly by calling set_os_workload_status() itself.

  The goal should be to have a single canonical source for status_set.

  This will affect all OpenStack charms that have optional relations.

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