Clarify environment variable usage when running in Docker

[antonok-edm]

This error message was quite confusing when setting up a Synapse server for the first time:

SYNAPSE_SERVER_NAME and SYNAPSE_CONFIG_PATH are mutually exclusive except in generate or migrate_config mode.

As someone who has had not used Synapse before, I wasn't sure how to resolve the error, and I ended up unsetting SYNAPSE_CONFIG_PATH. I figured this was safe because my config file was in the default location.

The server started working, but it was not until much later that I realized the config was not being used at all.

I've reworked the message to the following:

SYNAPSE_SERVER_NAME can only be combined with SYNAPSE_CONFIG_PATH in generate or migrate_config mode. To start synapse using a config file, unset the SYNAPSE_SERVER_NAME environment variable.

This should make it more clear as to which variable is the preferred method of configuration.

[richvdh]

thanks, that is indeed clearer. Please could you sign off your contribution as per https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#sign-off?

[richvdh]

@antonok-edm : I'm afraid we can't use this without a sign-off. please could you add one?

Let us know if the process isn't clear.

[antonok-edm]

I'd prefer not to leave my email laying around, but feel free to either use this or claim the contribution as your own:

Signed-off-by: Anton Lazarev https://antonok.com

[richvdh]

That's fine, we don't need an email address. Thanks!