pacemaker-remote-relation-changed hook errors on trigger-corosync-update

[Aurelien Lourot]

Seen in the charm-masakari-monitors gate. [0][1] At deploy time the charm-hacluster's pacemaker-remote-relation-changed hook errors with

----------
ERROR permission denied
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-hacluster-0/charm/hooks/pacemaker-remote-relation-changed", line 752, in <module>
    hooks.execute(sys.argv)
  File "/var/lib/juju/agents/unit-hacluster-0/charm/charmhelpers/core/hookenv.py", line 945, in execute
    self._hooks[hook_name]()
  File "/var/lib/juju/agents/unit-hacluster-0/charm/hooks/pacemaker-remote-relation-changed", line 340, in ha_relation_changed
    trigger_corosync_update_from_leader(
  File "/var/lib/juju/agents/unit-hacluster-0/charm/hooks/utils.py", line 1597, in trigger_corosync_update_from_leader
    corosync_update_uuid = relation_get(
  File "/var/lib/juju/agents/unit-hacluster-0/charm/charmhelpers/core/hookenv.py", line 93, in wrapper
    res = func(*args, **kwargs)
  File "/var/lib/juju/agents/unit-hacluster-0/charm/charmhelpers/core/hookenv.py", line 470, in relation_get
    return json.loads(subprocess.check_output(_args).decode('UTF-8'))
  File "/usr/lib/python3.8/subprocess.py", line 411, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/usr/lib/python3.8/subprocess.py", line 512, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['relation-get', '--format=json', '-r', 'hanode:3', 'trigger-corosync-update', 'pacemaker-remote/0']' returned non-zero exit status 1.
----------

This code path was introduced recently [2] while implementing the new `update-ring` action. [3] Unfortunately ha_relation_changed() is not only called in `ha` relation hooks but also in other relations, which then leads to this error.

[0] https://review.opendev.org/c/openstack/charm-masakari-monitors/+/776366
[1] https://openstack-ci-reports.ubuntu.com/artifacts/test_charm_pipeline_func_smoke/openstack/charm-masakari-monitors/776366/2/22687/index.html
[2] https://review.opendev.org/c/openstack/charm-hacluster/+/741592/36/hooks/hooks.py
[3] lp:1400481

[Aurelien Lourot (aurelien-lourot)]

Fix: https://review.opendev.org/c/openstack/charm-hacluster/+/781655