rabbit_prelaunch_early_logging: Configure rabbit_log as a Logger ha…

…ndler

Currently, when the new Logger API exposed by Erlang is being used by an
application, messages are lost once Lager is configured. That is because
Lager does not know about Logger in this context.

To fix this, `rabbit_log` is configured as a Logger handler which calls
Lager API. This means that Logger messages are passed to Lager.

Logger's log level is to set to pass all messages (including debug).
Message routing/filtering is done by Lager instead.

This change depends on new log/2 function being added to the
`rabbit_log` module in rabbitmq-common.

apps/rabbitmq_prelaunch/src/rabbit_prelaunch_early_logging.erl

@@ -26,6 +26,7 @@ get_default_log_level() ->
 
 do_setup_early_logging(#{log_levels := LogLevels} = Context,
                        LagerEventToStdout) ->
+    redirect_logger_messages_to_lager(),
     Colored = use_colored_logging(Context),
     application:set_env(lager, colored, Colored),
     ConsoleBackend = lager_console_backend,
@@ -50,6 +51,11 @@ do_setup_early_logging(#{log_levels := LogLevels} = Context,
       end, list_expected_sinks()),
     ok.
 
+redirect_logger_messages_to_lager() ->
+    io:format(standard_error, "Configuring logger redirection~n", []),
+    ok = logger:add_handler(rabbit_log, rabbit_log, #{}),
+    ok = logger:set_primary_config(level, all).
+
 use_colored_logging() ->
     use_colored_logging(rabbit_prelaunch:get_context()).