oslo.cache is noisy on startup if memcache is missing

[Stephen Finucane]

When running unit tests in nova, we see the following error message quite regularly:

  2021-08-17 11:54:58.368 27961 ERROR stevedore.extension [req-ac3ac729-e3f6-4977-95ac-f3a2b8bb7457 fake_user 6a6a9c9eee154e9cb8cec487b98d36ab - - -] Could not load 'oslo_cache.memcache_pool': No module named 'memcache': ModuleNotFoundError: No module named 'memcache'
  2021-08-17 11:54:58.375 27959 ERROR stevedore.extension [req-3c345bf7-7af2-43b7-aa63-fe6274991b2e fake_user 6a6a9c9eee154e9cb8cec487b98d36ab - - -] Could not load 'oslo_cache.memcache_pool': No module named 'memcache': ModuleNotFoundError: No module named 'memcache'
  2021-08-17 11:54:58.393 27962 ERROR stevedore.extension [req-8f167a6a-ca66-4386-9dad-78ae4e63173a fake_user 6a6a9c9eee154e9cb8cec487b98d36ab - - -] Could not load 'oslo_cache.memcache_pool': No module named 'memcache': ModuleNotFoundError: No module named 'memcache'
  2021-08-17 11:54:58.545 27960 ERROR stevedore.extension [req-64210d11-2585-477c-8dac-07bd12ba72c2 fake_user 6a6a9c9eee154e9cb8cec487b98d36ab - - -] Could not load 'oslo_cache.memcache_pool': No module named 'memcache': ModuleNotFoundError: No module named 'memcache'

By stopping the process at the right time, we see the following exception:

    File "/opt/stack/nova/tests/unit/test_availability_zones.py", line 34, in <module>
      class AvailabilityZoneTestCases(test.TestCase):
    File "/opt/stack/nova/tests/unit/test_availability_zones.py", line 254, in AvailabilityZoneTestCases
      @mock.patch.object(az._get_cache(), 'get')
    File "/opt/stack/nova/availability_zones.py", line 36, in _get_cache
      MC = cache_utils.get_client(expiration_time=AZ_CACHE_SECONDS)
    File "/opt/stack/nova/cache_utils.py", line 58, in get_client
      backend='oslo_cache.dict'))
    File "/opt/stack/nova/cache_utils.py", line 96, in _get_custom_cache_region
      region.configure(backend, **region_params)
    File "/opt/stack/.tox/py36/lib/python3.6/site-packages/dogpile/cache/region.py", line 480, in configure
      backend_cls = _backend_loader.load(backend)
    File "/opt/stack/.tox/py36/lib/python3.6/site-packages/dogpile/util/langhelpers.py", line 47, in load
      self._mgr = stevedore.ExtensionManager(self.group)
    File "/opt/stack/.tox/py36/lib/python3.6/site-packages/stevedore/extension.py", line 136, in __init__
      verify_requirements)
    File "/opt/stack/.tox/py36/lib/python3.6/site-packages/stevedore/extension.py", line 243, in _load_plugins
      exc_info=LOG.isEnabledFor(logging.DEBUG))
  Message: 'Could not load %r: %s'
  Arguments: ('oslo_cache.memcache_pool', ModuleNotFoundError("No module named 'memcache'",))

I've yet to figure out how to silence these errors or whether it's actually nova that needs to change something, but I suspect we might need configure stevedore slightly differently.

Leaving this here so I remember to investigate in the future.

[Daniel Bengtsson (damani42)]

Hi,

Do you have any update it's still relevant? Do you still plan to work on it?

[Stephen Finucane (stephenfinucane)]

Still an issue. Still planning to work on it. Haven't done so yet.

[Daniel Bengtsson (damani42)]

Ok, thanks a lot for the answer.