Allow custom log_levels

[zoidyzoidzoid]

Closes #118

[zoidyzoidzoid]

Tested with:

docker run -it --rm -e RABBITMQ_LOG_LEVELS='[{connection, error}]' $IMAGE_ID

[tianon]

So far we've avoided exposing the user to any raw Erlang configuration in any of our environment variables, and especially considering that the 3.7 version of RabbitMQ is moving to a configuration file that's INI-based, I'd like to continue sticking to that.

[michaelklishin]

@tianon the Erlang term config format isn't going away, in fact, some things have such as complex structure that I don't think they can be moved to the .ini-style format. In 3.7.0 it will be a separate config file, though, and most things will use the .ini one. JFYI.

[michaelklishin]

Config settings can be passed on the command line, e.g.

RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="-rabbit log_levels [{connection,error}]" rabbitmq-server

which is an Erlang/OTP feature: -rabbit key value on the command line is the same as setting rabbit.key to value in the Erlang term config file.

[michaelklishin]

@tianon in this particular case, the value of log_levels seems to be treated (passed on) as a string, so you don't necessarily run much risk in whitelisting it.

More complicated cases (e.g. LDAP queries) should be configured by providing a file IMO.

[tianon]

Ooooh, we should definitely document RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS -- that way we could stop doing so many of these one-off environment variables! 😄 Does that mean -rabbit could be specified more than once?

ala, RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="-rabbit log_levels [{connection,error}] -rabbit something <<'somevalue'>>" ?

Good to know regarding the ini-style config -- will keep that in mind. 😅

[michaelklishin]

@tianon no, it would be -rabbit key1 value1 key2 value 2. See section 8.8 in this Erlang guide.

[zoidyzoidzoid]

I guess that makes this PR related to this one as well: #138

😋

[ilude]

See Pull request #187

Sorry, I did not intent to reopen this. Only to add a reference so other googlers could find a solution.