config-changed chown: cannot access '/srv/nova/instances': No such file or directory

[Ryan Beisner]

xenial-queens, master charms pre-18.05:

The nova-compute charm traces trying to chown the instance storage directory because it does not yet exist.

2018-05-15 11:00:36 INFO juju-log Generating new ssh key for user nova.
2018-05-15 11:00:36 DEBUG worker.uniter.jujuc server.go:178 running hook tool "relation-get"
2018-05-15 11:00:36 DEBUG config-changed ERROR no relation id specified
2018-05-15 11:00:36 DEBUG worker.uniter.jujuc server.go:178 running hook tool "relation-get"
2018-05-15 11:00:36 DEBUG config-changed ERROR no relation id specified
2018-05-15 11:00:36 DEBUG config-changed chown: cannot access '/srv/nova/instances': No such file or directory
2018-05-15 11:00:36 DEBUG config-changed Traceback (most recent call last):
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/config-changed", line 579, in <module>
2018-05-15 11:00:36 DEBUG config-changed main()
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/config-changed", line 572, in main
2018-05-15 11:00:36 DEBUG config-changed hooks.execute(sys.argv)
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/charmhelpers/core/hookenv.py", line 823, in execute
2018-05-15 11:00:36 DEBUG config-changed self._hooks[hook_name]()
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/charmhelpers/contrib/openstack/utils.py", line 1449, in wrapped_f
2018-05-15 11:00:36 DEBUG config-changed restart_functions)
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/charmhelpers/core/host.py", line 730, in restart_on_change_helper
2018-05-15 11:00:36 DEBUG config-changed r = lambda_f()
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/charmhelpers/contrib/openstack/utils.py", line 1448, in <lambda>
2018-05-15 11:00:36 DEBUG config-changed (lambda: f(*args, **kwargs)), restart_map, stopstart,
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/charmhelpers/contrib/hardening/harden.py", line 79, in _harden_inner2
2018-05-15 11:00:36 DEBUG config-changed return f(*args, **kwargs)
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/config-changed", line 195, in config_changed
2018-05-15 11:00:36 DEBUG config-changed fix_path_ownership(fp, user='nova')
2018-05-15 11:00:36 DEBUG config-changed File "/var/lib/juju/agents/unit-nova-compute-0/charm/hooks/nova_compute_utils.py", line 669, in fix_path_ownership
2018-05-15 11:00:36 DEBUG config-changed check_call(cmd)
2018-05-15 11:00:36 DEBUG config-changed File "/usr/lib/python3.5/subprocess.py", line 581, in check_call
2018-05-15 11:00:36 DEBUG config-changed raise CalledProcessError(retcode, cmd)
2018-05-15 11:00:36 DEBUG config-changed subprocess.CalledProcessError: Command '['chown', 'nova', '/srv/nova/instances']' returned non-zero exit status 1
2018-05-15 11:00:36 ERROR juju.worker.uniter.operation runhook.go:113 hook "config-changed" failed: exit status 1
2018-05-15 11:00:36 DEBUG juju.worker.uniter.operation executor.go:84 lock released
2018-05-15 11:00:36 INFO juju.worker.uniter resolver.go:100 awaiting error resolution for "config-changed" hook
2018-05-15 11:00:36 DEBUG juju.worker.uniter agent.go:17 [AGENT-STATUS] error: hook failed: "config-changed"
2018-05-15 11:00:36 INFO juju.worker.uniter resolver.go:100 awaiting error resolution for "config-changed" hook

.

#### Workaround:
juju run --application nova-compute "sudo mkdir -vp /srv/nova/instances"
juju resolved nova-compute/0
juju resolved nova-compute/1
juju resolved nova-compute/2
juju resolved nova-compute/3

[Alex Kavanagh (ajkavanagh)]

So '/srv/nova/instances' comes from the config.yaml 'instances-path', which has a default of /var/lib/nova/instances -- so it must be set for this to happen.

Options:

 1. Not do the action of setting the permissions if the lib doesn't exist.
 2. Create the directory and then set the permissions, if it doesn't exist.