error log is produced for etcd3gw backend even when not using it

[Pavlo Shchelokovskyy]

We deploy OpenStack in containers, and use only memcached backend, not installing dependencies of other backends into the containers

on many services (e.g. Neutron, Keystone) we see the following errors:

2021-05-13 07:40:38.529 18 ERROR stevedore.extension [req-e5eecc70-adbe-4aa6-8325-a6f07c7d4a0a 38ffa727563a4ca3b6abda26d60e3494 0ed296340f02481ab60bb0bbdc03cfe0 - 0d654ccd0eb647e9badd34fdfe
746b67 0d654ccd0eb647e9badd34fdfe746b67] Could not load 'oslo_cache.etcd3gw': No module named 'etcd3gw': ModuleNotFoundError: No module named 'etcd3gw

even if our cache is explicitly configured to use memcached:

[cache]
backend = oslo_cache.memcache_pool
memcache_secret_key = eD6SEGCYNIMSyIWG
memcache_security_strategy = ENCRYPT
memcached_servers = openstack-memcached-memcached-0.memcached.openstack.svc.cluster.local:11211,openstack-memcached-memcached-1.memcached.openstack.svc.cluster.local:11211,openstack-memcached-memcached-2.memcached.openstack.svc.cluster.local:11211

Since it seems that the plugin lookup and loading code is actually in the dogpile.cache lib,
the solution would be for etcd3gw backend to use lazy imports similar to e.g. what mongodb backend does in the oslo.cache already https://opendev.org/openstack/oslo.cache/src/branch/master/oslo_cache/backends/mongo.py#L331-L333

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/oslo.cache/+/792677

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.cache/+/792677
Committed: https://opendev.org/openstack/oslo.cache/commit/40946a9349407f36a43d5020d991085c11468698
Submitter: "Zuul (22348)"
Branch: master

commit 40946a9349407f36a43d5020d991085c11468698
Author: Mitya_Eremeev <email address hidden>
Date: Fri May 21 19:50:53 2021 +0300

    Don't import module "etcd3gw" if etcd3gw backend is not used.

    If module etcd3gw is not required for used backend,
    then no need to have it installed and imported.
    Otherwise we always have ugly log error:
    Could not load 'oslo_cache.etcd3gw': No module named 'etcd3gw': ModuleNotFoundError: No module named 'etcd3gw

    Closes-Bug: 1928318
    Change-Id: Icbe6dc3e93b4d2fec1ceb88366027294e49d7032

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.cache 2.8.1 release.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/oslo.cache/+/822671

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.cache/+/822671
Committed: https://opendev.org/openstack/oslo.cache/commit/3df5e9001346d17994deb8db60361cf8589a6230
Submitter: "Zuul (22348)"
Branch: stable/wallaby

commit 3df5e9001346d17994deb8db60361cf8589a6230
Author: Mitya_Eremeev <email address hidden>
Date: Fri May 21 19:50:53 2021 +0300

    Don't import module "etcd3gw" if etcd3gw backend is not used.

    If module etcd3gw is not required for used backend,
    then no need to have it installed and imported.
    Otherwise we always have ugly log error:
    Could not load 'oslo_cache.etcd3gw': No module named 'etcd3gw': ModuleNotFoundError: No module named 'etcd3gw

    Closes-Bug: 1928318
    Change-Id: Icbe6dc3e93b4d2fec1ceb88366027294e49d7032
    (cherry picked from commit 40946a9349407f36a43d5020d991085c11468698)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.cache 2.7.1 release.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/victoria
Review: https://review.opendev.org/c/openstack/oslo.cache/+/844273

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.cache/+/844273
Committed: https://opendev.org/openstack/oslo.cache/commit/f0ddb8a63f8b36224b365c962004f17f83dd5ca4
Submitter: "Zuul (22348)"
Branch: stable/victoria

commit f0ddb8a63f8b36224b365c962004f17f83dd5ca4
Author: Mitya_Eremeev <email address hidden>
Date: Fri May 21 19:50:53 2021 +0300

    Don't import module "etcd3gw" if etcd3gw backend is not used.

    If module etcd3gw is not required for used backend,
    then no need to have it installed and imported.
    Otherwise we always have ugly log error:
    Could not load 'oslo_cache.etcd3gw': No module named 'etcd3gw': ModuleNotFoundError: No module named 'etcd3gw

    Closes-Bug: 1928318
    Change-Id: Icbe6dc3e93b4d2fec1ceb88366027294e49d7032
    (cherry picked from commit 40946a9349407f36a43d5020d991085c11468698)
    (cherry picked from commit 3df5e9001346d17994deb8db60361cf8589a6230)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/ussuri
Review: https://review.opendev.org/c/openstack/oslo.cache/+/848727

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.cache/+/848727
Committed: https://opendev.org/openstack/oslo.cache/commit/978a093b2357b5c7af29e248987ce61f0656358a
Submitter: "Zuul (22348)"
Branch: stable/ussuri

commit 978a093b2357b5c7af29e248987ce61f0656358a
Author: Mitya_Eremeev <email address hidden>
Date: Fri May 21 19:50:53 2021 +0300

    Don't import module "etcd3gw" if etcd3gw backend is not used.

    If module etcd3gw is not required for used backend,
    then no need to have it installed and imported.
    Otherwise we always have ugly log error:
    Could not load 'oslo_cache.etcd3gw': No module named 'etcd3gw': ModuleNotFoundError: No module named 'etcd3gw

    Closes-Bug: 1928318
    Change-Id: Icbe6dc3e93b4d2fec1ceb88366027294e49d7032
    (cherry picked from commit 40946a9349407f36a43d5020d991085c11468698)
    (cherry picked from commit 3df5e9001346d17994deb8db60361cf8589a6230)
    (cherry picked from commit f0ddb8a63f8b36224b365c962004f17f83dd5ca4)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/train
Review: https://review.opendev.org/c/openstack/oslo.cache/+/848858

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.cache/+/848858
Committed: https://opendev.org/openstack/oslo.cache/commit/c6fb9987419d6f497d97dcd7590cbc32e134e435
Submitter: "Zuul (22348)"
Branch: stable/train

commit c6fb9987419d6f497d97dcd7590cbc32e134e435
Author: Mitya_Eremeev <email address hidden>
Date: Fri May 21 19:50:53 2021 +0300

    Don't import module "etcd3gw" if etcd3gw backend is not used.

    If module etcd3gw is not required for used backend,
    then no need to have it installed and imported.
    Otherwise we always have ugly log error:
    Could not load 'oslo_cache.etcd3gw': No module named 'etcd3gw': ModuleNotFoundError: No module named 'etcd3gw

    Closes-Bug: 1928318
    Change-Id: Icbe6dc3e93b4d2fec1ceb88366027294e49d7032
    (cherry picked from commit 40946a9349407f36a43d5020d991085c11468698)
    (cherry picked from commit 3df5e9001346d17994deb8db60361cf8589a6230)
    (cherry picked from commit f0ddb8a63f8b36224b365c962004f17f83dd5ca4)
    (cherry picked from commit 978a093b2357b5c7af29e248987ce61f0656358a)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.cache train-eol release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.cache victoria-eom release.