Many settings as defined in settings.py do not respect the documented environment variables

[glennmatthews]

Environment

• Nautobot version (Docker tag too if applicable): 1.4.5
• Python version: any
• Database platform, version: any
• Middleware(s): n/a

Steps to Reproduce

1. Use a minimal, stripped-down nautobot_config.py, rather than one containing all optional settings like the nautobot/core/templates/nautobot_config.py.j2 template does.
2. Attempt to influence various optional settings by setting environment variables for the Nautobot process, e.g. NAUTOBOT_DEBUG=True

Expected Behavior

Environment variables should be respected as documented.

Observed Behavior

Many environment variables are not respected by the defaults defined in settings.py, only the overrides for these settings in nautobot_config.py.j2 respect environment variables. Related: #2574. The below list may not be comprehensive:

• CACHEOPS_DEFAULTS / NAUTOBOT_CACHEOPS_DEFAULTS
• CACHEOPS_ENABLED / NAUTOBOT_CACHEOPS_ENABLED
• CACHEOPS_REDIS / NAUTOBOT_CACHEOPS_REDIS
• CORS_ALLOW_ALL_ORIGINS / NAUTOBOT_CORS_ALLOW_ALL_ORIGINS
• DEBUG / NAUTOBOT_DEBUG
• DISABLE_PREFIX_LIST_HIERARCHY / NAUTOBOT_DISABLE_PREFIX_LIST_HIERARCHY (making this inherit from a variable by default would possibly break our Constance config though)
• ENFORCE_GLOBAL_UNIQUE / NAUTOBOT_ENFORCE_GLOBAL_UNIQUE
• MAINTENANCE_MODE / NAUTOBOT_MAINTENANCE_MODE
• METRICS_ENABLED / NAUTOBOT_METRICS_ENABLED
• SESSION_COOKIE_AGE / NAUTOBOT_SESSION_COOKIE_AGE
• SESSION_FILE_PATH / NAUTOBOT_SESSION_FILE_PATH
• STRICT_FILTERING / NAUTOBOT_STRICT_FILTERING
• TIME_ZONE / NAUTOBOT_TIME_ZONE, as well as all of the related time/date format variables

Solution should probably be to just strip down nautobot_config.py.j2 and move the environment variable checks directly into settings.py.

This also relates to #1150.

[jathanism]

• METRICS_ENABLED / NAUTOBOT_METRICS_ENABLED

This one can't easily be set as an environment variable because it's a "magic" setting that is interpreted.

The magic variable is processed inside of nautobot.core.cli._configure_settings, so if an environment variable were to be read, it would have to be done so in this code block:

    # If metrics are enabled and postgres is the backend, set the driver to the
    # one provided by django-prometheus.
    if settings.METRICS_ENABLED and "postgres" in settings.DATABASES["default"]["ENGINE"]:
        settings.DATABASES["default"]["ENGINE"] = "django_prometheus.db.backends.postgresql"

I would rather us eliminate this setting entirely in exchange for just having users explicitly set the metrics backend by just setting this in nautobot_config.py:

DATABASES["default"]["ENGINE"] = "django_prometheus.db.backends.postgresql"

Obviously, this latter approach would require revising our documentation on enabling metrics.