Add rabbit_tracer boot step for running Looking Glass

It will run only if RABBITMQ_TRACER is defined. It contain a
list of M:F (for example RABBITMQ_TRACER="abc:def,ghi:jkl")
that are functions returning Looking Glass trace specifications.

This commit comes with one such function, rabbit_tracer:connections.
It will trace all existing and future connection processes across
all rabbit and rabbit_common applications.

More functions will need to be added to trace specific parts of
RabbitMQ, or to trace plugins. For example there could be functions
for tracing channels, or data collection for management. Trace
specifications can be combined to get the target you need.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/rabbit.erl b/src/rabbit.erl
index 5ae58f57d1..3bc669d9f6 100644
--- a/src/rabbit.erl
+++ b/src/rabbit.erl
@@ -219,6 +219,11 @@
                                    [rabbit_core_metrics_gc]}},
                     {enables,     networking}]}).
 
+-rabbit_boot_step({rabbit_tracer,
+                   [{description, "Looking Glass tracer and profiler"},
+                    {mfa,         {rabbit_tracer, boot, []}},
+                    {requires,    networking}]}).
+
 %%---------------------------------------------------------------------------
 
 -include("rabbit_framing.hrl").