default_enabled_filters nova.conf updates don't get written on openstack upgrade

[Corey Bryant]

While testing https://bugs.launchpad.net/charm-nova-cloud-controller/+bug/2036766 with updated filters in
default_enabled_filters() (called by NovaConfigContext), the new filters aren't getting rendered to nova.conf after the openstack upgrade in the config-changed hook.

On the upgrade from antelope->bobcat, the following call to os_release() is returning a cached version of "antelope".

def default_enabled_filters():
    os_rel = ch_utils.os_release('nova-common')
    if cmp_os_rel >= 'bobcat':
        return _bobcat_enabled_filters
    if cmp_os_rel >= 'victoria':
        return _victoria_enabled_filters
    if cmp_os_rel >= 'pike':

There's a reset_cache parameter for os_release(), but in this case it didn't change anything because os_release() calls into other functions that don't account for that parameter.

On down the line os_release() ends up getting the release from get_installed_os_version() which calls openstack_release():

@cached
def openstack_release():
    """Return /etc/os-release in a dict."""
    d = {}
    try:
        with open('/etc/openstack-release', 'r') as lsb:
            for l in lsb:
                s = l.split('=')
                if len(s) != 2:
                    continue
                d[s[0].strip()] = s[1].strip()
    except FileNotFoundError:
        pass
    return d

Removing the @cached decorator from this function allows "bobcat" to get returned and the nova.conf rendered correctly. I don't know that the caching is really necessary here since there is already caching at a higher level function.

[Corey Bryant (corey.bryant)]

See testing performed for this bug at https://bugs.launchpad.net/charm-nova-cloud-controller/+bug/2036766/comments/1

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-nova-cloud-controller/+/895840
Committed: https://opendev.org/openstack/charm-nova-cloud-controller/commit/5cf66c87c797e4f7549bc7cd9f5d57c624d30d00
Submitter: "Zuul (22348)"
Branch: master

commit 5cf66c87c797e4f7549bc7cd9f5d57c624d30d00
Author: Corey Bryant <email address hidden>
Date: Tue Sep 19 14:00:33 2023 -0400

    Drop AvailabilityZoneFilter inline with upstream removal

    The was removed from upstream nova in the 2023.2 cycle
    via commit 5edd805fe2395f35ecdfe5b589a51dc00565852f.

    The nova release note states:

    The ``AvailabilityZoneFilter`` was deprecated for removal
    in 24.0.0 (Xena) and has now been removed.
    The functionality of the``AvailabilityZoneFilter`` has been
    replaced by the``map_az_to_placement_aggregate`` pre-filter.
    The pre-filter was introduced in 18.0.0 (Rocky) and enabled
    by default in 24.0.0 (Xena). This pre-filter is now always
    enabled and the ``[scheduler] query_placement_for_availability_zone``
    config option has been removed.

    This change also syncs the charm-helpers change from:
    https://github.com/juju/charm-helpers/pull/850

    Closes-Bug: #2037751
    Closes-Bug: #2036766
    Change-Id: I315900a7e32ec66b27fa69961e9b7dcb9fa1f949

[Corey Bryant (corey.bryant)]

This charm-helpers change is likely needed in other charms/releases so I'm going to backport the change to wallaby+. It would only be needed as early as wallaby because that's where the openstack-release package was introduced:

openstack-release | 1.0ubuntu1~cloud0 | wallaby | focal-updates | source