Usage of dogpile.cache.backend.redis requires injection via backend_argument

[Takashi Kajinami]

Using redis backend always require usage of backend_arugment, which is considered advanced.
Because backend_argument is not secret, this means that password in the url may be leaked in logs.

In case we attempt to use the memcache_servers option, it always triggers the following traceback.

```
[Sat Feb 03 03:46:08.438124 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] mod_wsgi (pid=15934): Failed to exec Python script file '/var/www/cgi-bin/keystone/keystone'.
[Sat Feb 03 03:46:08.438153 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] mod_wsgi (pid=15934): Exception occurred processing WSGI script '/var/www/cgi-bin/keystone/keystone'.
[Sat Feb 03 03:46:08.439106 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] Traceback (most recent call last):
[Sat Feb 03 03:46:08.439128 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/var/www/cgi-bin/keystone/keystone", line 52, in <module>
[Sat Feb 03 03:46:08.439129 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] application = initialize_public_application()
[Sat Feb 03 03:46:08.439131 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/keystone/server/wsgi.py", line 23, in initialize_public_application
[Sat Feb 03 03:46:08.439132 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] return flask_core.initialize_application(
[Sat Feb 03 03:46:08.439134 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/keystone/server/flask/core.py", line 171, in initialize_application
[Sat Feb 03 03:46:08.439135 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] _unused, app = keystone.server.setup_backends(
[Sat Feb 03 03:46:08.439136 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/keystone/server/__init__.py", line 46, in setup_backends
[Sat Feb 03 03:46:08.439137 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] drivers = backends.load_backends()
[Sat Feb 03 03:46:08.439139 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/keystone/server/backends.py", line 42, in load_backends
[Sat Feb 03 03:46:08.439140 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] cache.configure_cache()
[Sat Feb 03 03:46:08.439141 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/keystone/common/cache/core.py", line 123, in configure_cache
[Sat Feb 03 03:46:08.439142 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] cache.configure_cache_region(CONF, region)
[Sat Feb 03 03:46:08.439143 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/oslo_cache/core.py", line 405, in configure_cache_region
[Sat Feb 03 03:46:08.439144 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] region.configure_from_config(config_dict,
[Sat Feb 03 03:46:08.439150 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/dogpile/cache/region.py", line 662, in configure_from_config
[Sat Feb 03 03:46:08.439151 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] return self.configure(
[Sat Feb 03 03:46:08.439153 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/dogpile/cache/region.py", line 487, in configure
[Sat Feb 03 03:46:08.439154 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] self.backend = backend_cls.from_config_dict(
[Sat Feb 03 03:46:08.439155 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/dogpile/cache/api.py", line 186, in from_config_dict
[Sat Feb 03 03:46:08.439156 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] return cls(
[Sat Feb 03 03:46:08.439157 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/dogpile/cache/backends/redis.py", line 305, in __init__
[Sat Feb 03 03:46:08.439159 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] super().__init__(
[Sat Feb 03 03:46:08.439160 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/dogpile/cache/backends/redis.py", line 124, in __init__
[Sat Feb 03 03:46:08.439161 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] self._create_client()
[Sat Feb 03 03:46:08.439162 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/dogpile/cache/backends/redis.py", line 333, in _create_client
[Sat Feb 03 03:46:08.439163 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] sentinel = redis.sentinel.Sentinel(
[Sat Feb 03 03:46:08.439165 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] File "/usr/lib/python3.9/site-packages/redis/sentinel.py", line 185, in __init__
[Sat Feb 03 03:46:08.439166 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] self.sentinels = [
[Sat Feb 03 03:46:08.439170 2024] [wsgi:error] [pid 15934:tid 15945] [remote 127.0.0.1:49472] TypeError: 'NoneType' object is not iterable
```

The snippet from keystone.conf
```
[cache]
backend=dogpile.cache.redis
memcache_servers=redis://:a_big_secret@localhost:6379
tls_enabled = true
tls_cafile = /etc/pki/tls/certs/ca-bundle.crt
```

[Takashi Kajinami (kajinamit)]

Hmm. It seems we are not supposed to use memcache_servers but set url via backend_arguments ?

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/oslo.cache/+/907649

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.cache/+/907649
Committed: https://opendev.org/openstack/oslo.cache/commit/28411250dadaf73f0263b55e1d07337fc79b202b
Submitter: "Zuul (22348)"
Branch: master

commit 28411250dadaf73f0263b55e1d07337fc79b202b
Author: Takashi Kajinami <email address hidden>
Date: Sat Feb 3 21:10:28 2024 +0900

    Add native options for redis backend

    This introduces a few new redis_* options to simplify the settings
    required to use the redis backend. The main aim of this change is to
    replace the requirement to inject url by backend_argument.

    [cache]
    backend=dogpile.cache.redis
    redis_server=127.0.0.1:6379
    redis_username=default
    redis_password=a_big_secret
    redis_socket_timeout=1.0

    Closes-Bug: #2052351
    Change-Id: Id72878f9cddaa99146eab5fb4ee76c8e6a633809

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.cache 3.7.0 release.