Docs: "environment variables" not clear

[vanschelven]

The configuration overview says

Gunicorn first reads environment variables for some configuration settings.

but if I actually look at the list of settings, it seems that this list is very limited.

Is this reading correct? If so, my documentation issue would be "this can be clarified". As it stands, to me the wording is somewhat suggestive that you might configured more via the environment (other than via GUNICORN_CMD_ARGS) but this is simply not so?

[pajod]

IMHO Explicit is better than implicit, so it should start with something like:

Gunicorn first inspects its environment for Systemd-specific variables ref:NOTIFY_SOCKET, ref:.. and the following configuration which have an ENV shorthands: ref:SENDFILE, ref:FORWARDED_ALLOW_IPS, ref:...

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Closely related "can be clarified" thoughts I noticed but have not yet submitted patches for:

• documentation should exemplify that shlex splitting is applied to GUNICORN_CMD_ARGS
• "environment" is not a singular thing. Documentation could be much more verbose spelling out what is parsed, what is available to workers/logging, what is available to the application
• The chdir and config setting interaction is impossible to explain in simple terms of precedence or parsing order. Some deployments probably just work by accident and get surprisingly broken by changed symlinks and restart behavior. My preference would be to add deprecation warnings to every "ambiguous" way of using both. And later reduce support to only what was reported as still useful to anyone, greatly simplifying correct & complete documentation. Because I suspect there is only launching Gunicorn via some sysvinit/systemd config, or via shell, not a mix of both where you pass the name but expect it to take the path from config.
• Python 3.9 provides first-class booleans in argparse, but --sendfile is not using that and the value parsing of the SENDFILE environment variable is not explained