Use Lager to log RabbitMQ messages

By default, RabbitMQ now logs messages to a single file
($RABBITMQ_LOGS). The $RABBITMQ_SASL_LOGS variable is unused. To
configure how and which messages are logged, it's recommended to do it
from rabbitmq.config, not from the environment variable.

The old `log_levels` parameter is unsupported and categories are
replaced by Lager extra sinks. If you had in your rabbitmq.config:
    {rabbit, [
        {log_levels, [{connection, info}]}
      ]}
You can now configure Lager like this:
    {lager, [
        {extra_sinks, [
            {rabbit_connection_lager_event, [
                {handlers, [{lager_forwarder_backend, [lager_event, info]}]}
              ]}
          ]}
      ]}

rabbitmq-build.mk from rabbitmq-common is included in the top-level
Makefile. It sets the appropriate compiler options to enable Lager's
lager_transform parse_transform module.

rabbit_log calls are now converted by this parse_transform to direct
calls to lager:log(). To keep backward compatibility with other plugins,
the rabbit_log module still implements all the <level>() functions.
Compared to the parse_transformed calls, the main difference is the
logged message does not carry the file:line metadata.

Fixes #94.

1 files changed, 40 insertions, 6 deletions

diff --git a/docs/rabbitmq.config.example b/docs/rabbitmq.config.example
index eacdb8a993..42280cc0f5 100644
--- a/docs/rabbitmq.config.example
+++ b/docs/rabbitmq.config.example
@@ -38,12 +38,6 @@
    %%
    %% {handshake_timeout, 10000},
 
-   %% Log levels (currently just used for connection logging).
-   %% One of 'debug', 'info', 'warning', 'error' or 'none', in decreasing
-   %% order of verbosity. Defaults to 'info'.
-   %%
-   %% {log_levels, [{connection, info}, {channel, info}]},
-
    %% Set to 'true' to perform reverse DNS lookups when accepting a
    %% connection. Hostnames will then be shown instead of IP addresses
    %% in rabbitmqctl and the management plugin.
@@ -659,5 +653,45 @@
    %% Set queries to determine which tags a user has
    %%
    %% {tag_queries, []}
+  ]},
+
+  %% Lager controls logging.
+  %% See https://github.com/basho/lager for more documentation
+  {lager, [
+   %%
+   %% Log direcrory, taken from the RABBITMQ_LOG_BASE env variable by default.
+   %% {log_root, "/var/log/rabbitmq"},
+   %%
+   %% All log messages go to the default "sink" configured with
+   %% the `handlers` parameter. By default, it has a single
+   %% lager_file_backend handler writing messages to "$nodename.log"
+   %% (ie. the value of $RABBIT_LOGS).
+   %% {handlers, [
+   %%   {lager_file_backend, [{file, "rabbit.log"},
+   %%                         {level, info},
+   %%                         {date, ""},
+   %%                         {size, 0}]}
+   %% ]},
+   %%
+   %% Extra sinks are used in RabbitMQ to categorize messages. By
+   %% default, those extra sinks are configured to forward messages
+   %% to the default sink (see above). "rabbit_log_lager_event"
+   %% is the default category where all RabbitMQ messages without
+   %% a category go. Messages in the "channel" category go to the
+   %% "rabbit_channel_lager_event" Lager extra sink, and so on.
+   %% {extra_sinks, [
+   %%   {rabbit_log_lager_event, [{handlers, [
+   %%                               {lager_forwarder_backend,
+   %%                                [lager_event, info]}]}]},
+   %%   {rabbit_channel_lager_event, [{handlers, [
+   %%                                   {lager_forwarder_backend,
+   %%                                    [lager_event, info]}]}]},
+   %%   {rabbit_conection_lager_event, [{handlers, [
+   %%                                     {lager_forwarder_backend,
+   %%                                      [lager_event, info]}]}]},
+   %%   {rabbit_mirroring_lager_event, [{handlers, [
+   %%                                     {lager_forwarder_backend,
+   %%                                      [lager_event, info]}]}]}
+   %% ]}
   ]}
 ].