Merge pull request #10989 from rabbitmq/md/boot-avoid-module-scan

Avoid loading all modules during boot

Author: michaelklishin

deps/rabbit/src/rabbit.erl

@@ -1014,6 +1014,20 @@ do_run_postlaunch_phase(Plugins) ->
         ?LOG_DEBUG(""),
         ?LOG_DEBUG("== Plugins (postlaunch phase) =="),
 
+        %% Before loading plugins, set the prometheus collectors and
+        %% instrumenters to the empty list. By default, prometheus will attempt
+        %% to find all implementers of its collector and instrumenter
+        %% behaviours by scanning all available modules during application
+        %% start. This can take significant time (on the order of seconds) due
+        %% to the large number of modules available.
+        %%
+        %% * Collectors: the `rabbitmq_prometheus' plugin explicitly registers
+        %%   all collectors.
+        %% * Instrumenters: no instrumenters are used.
+        _ = application:load(prometheus),
+        ok = application:set_env(prometheus, collectors, [default]),
+        ok = application:set_env(prometheus, instrumenters, []),
+
         %% However, we want to run their boot steps and actually start
         %% them one by one, to ensure a dependency is fully started
         %% before a plugin which depends on it gets a chance to start.

deps/rabbitmq_management/src/rabbit_mgmt_dispatcher.erl

@@ -63,8 +63,18 @@ build_module_routes(Ignore) ->
     Routes = [Module:dispatcher() || Module <- modules(Ignore)],
     [{"/api" ++ Path, Mod, Args} || {Path, Mod, Args} <- lists:append(Routes)].
 
-modules(IgnoreApps) ->
-    [Module || {App, Module, Behaviours} <-
+modules(IgnoreApps0) ->
+    Apps0 = rabbit_misc:rabbitmq_related_apps(),
+    Apps = case IgnoreApps0 of
+               [] ->
+                   Apps0;
+               _ ->
+                   IgnoreApps = sets:from_list(IgnoreApps0, [{version, 2}]),
+                   lists:filter(
+                     fun(App) -> not sets:is_element(App, IgnoreApps) end,
+                     Apps0)
+           end,
+    [Module || {_App, Module, Behaviours} <-
                %% Sort rabbitmq_management modules first. This is
                %% a microoptimization because most files belong to
                %% this application. Making it first avoids several
@@ -76,8 +86,7 @@ modules(IgnoreApps) ->
                      (_, {rabbitmq_management, _, _}) -> false;
                      ({A, _, _}, {B, _, _})           -> A =< B
                  end,
-                 rabbit_misc:all_module_attributes(behaviour)),
-               not lists:member(App, IgnoreApps),
+                 rabbit_misc:module_attributes_from_apps(behaviour, Apps)),
                lists:member(rabbit_mgmt_extension, Behaviours)].
 
 module_app(Module) ->