Merge pull request #13201 from rabbitmq/rabbitmq-server-13194

By @frederikbosch: Peer discovery: add an option to opt out of registration

deps/rabbit/priv/schema/rabbit.schema

@@ -1370,6 +1370,13 @@ fun(Conf) ->
     end
 end}.
 
+%% Register node during cluster formation when backend supports registration.
+%%
+
+{mapping, "cluster_formation.registration.enabled", "rabbit.cluster_formation.perform_registration", [
+    {datatype, {enum, [true, false]}}
+]}.
+
 %% Cluster formation: lock acquisition retries as passed to https://erlang.org/doc/man/global.html#set_lock-3
 %%
 %% Currently used in classic, k8s, and aws peer discovery backends.

deps/rabbit/src/rabbit_peer_discovery.erl

@@ -46,6 +46,9 @@
 %% a new cluster as a virgin node
 -define(DEFAULT_NODE_TYPE, disc).
 
+%% Register node by default (with the backends that support registration)
+-define(PERFORM_REGISTRATION_BY_DEFAULT, true).
+
 %% default node prefix to attach to discovered hostnames
 -define(DEFAULT_PREFIX, "rabbit").
 
@@ -82,6 +85,16 @@ node_type() ->
             ?DEFAULT_NODE_TYPE
     end.
 
+-spec should_perform_registration() -> true | false.
+
+should_perform_registration() ->
+    case application:get_env(rabbit, cluster_formation) of
+        {ok, Proplist} ->
+            proplists:get_value(perform_registration, Proplist, ?PERFORM_REGISTRATION_BY_DEFAULT);
+        undefined ->
+            ?PERFORM_REGISTRATION_BY_DEFAULT
+    end.
+
 -spec lock_acquisition_failure_mode() -> ignore | fail.
 
 lock_acquisition_failure_mode() ->
@@ -968,18 +981,26 @@ error_description({invalid_cluster_node_type, BadType}) ->
 -spec maybe_register() -> ok.
 
 maybe_register() ->
-    Backend = persistent_term:get(?PT_PEER_DISC_BACKEND, backend()),
-    case Backend:supports_registration() of
+    case should_perform_registration() of
         true ->
-            ?LOG_DEBUG(
-               "Peer discovery: registering this node",
-               #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
-            register(Backend),
-            _ = Backend:post_registration(),
-            ok;
+            Backend = persistent_term:get(?PT_PEER_DISC_BACKEND, backend()),
+            case Backend:supports_registration() of
+                true ->
+                    ?LOG_DEBUG(
+                       "Peer discovery: registering this node",
+                       #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
+                    register(Backend),
+                    _ = Backend:post_registration(),
+                    ok;
+                false ->
+                    ?LOG_DEBUG(
+                       "Peer discovery: registration is not supported, skipping it",
+                       #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
+                    ok
+            end;
         false ->
             ?LOG_DEBUG(
-               "Peer discovery: registration unsupported, skipping register",
+               "Peer discovery: registration is disabled via configuration, skipping it",
                #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
             ok
     end.
@@ -987,16 +1008,24 @@ maybe_register() ->
 -spec maybe_unregister() -> ok.
 
 maybe_unregister() ->
-    Backend = persistent_term:get(?PT_PEER_DISC_BACKEND),
-    case Backend:supports_registration() of
+    case should_perform_registration() of
         true ->
-            ?LOG_DEBUG(
-               "Peer discovery: unregistering this node",
-               #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
-            unregister(Backend);
+            Backend = persistent_term:get(?PT_PEER_DISC_BACKEND),
+            case Backend:supports_registration() of
+                true ->
+                    ?LOG_DEBUG(
+                       "Peer discovery: unregistering this node",
+                       #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
+                    unregister(Backend);
+                false ->
+                    ?LOG_DEBUG(
+                       "Peer discovery: registration is not supported, skipping unregistration",
+                       #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
+                    ok
+            end;
         false ->
             ?LOG_DEBUG(
-               "Peer discovery: registration unsupported, skipping unregister",
+               "Peer discovery: registration is disabled via configuration, skipping unregistration",
                #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
             ok
     end.

deps/rabbit/test/config_schema_SUITE_data/rabbit.snippets

@@ -310,6 +310,25 @@ cluster_formation.dns.hostname = discovery.eng.example.local",
    ]}],
  []},
 
+ %% registration is enabled by default for the backends that support it
+ {cluster_formation_explicitly_enable_of_registration,
+   "cluster_formation.registration.enabled = true",
+   [{rabbit,
+        [{cluster_formation, [
+          {perform_registration, true}
+         ]}]
+   }],
+   []},
+
+  {cluster_formation_opt_out_of_registration,
+   "cluster_formation.registration.enabled = false",
+   [{rabbit,
+        [{cluster_formation, [
+          {perform_registration, false}
+         ]}]
+   }],
+   []},
+
  {tcp_listen_options,
   "tcp_listen_options.backlog = 128
 tcp_listen_options.nodelay = true