Classic config peer discovery: conditionally support registration

If registration is supported, a randomized delay will be injected. It makes
sense to support it in this config, in fact, our own test suites are evidence
of that: they start all nodes in parallel.

However, this backend is used by default so even a blank single node would
then wait on a delay that serves no purpose. So we make this conditional:
if no peer nodes are configured we don't want to induce any delays.

Pair: @dumbbell.

1 files changed, 19 insertions, 1 deletions

diff --git a/src/rabbit_peer_discovery_classic_config.erl b/src/rabbit_peer_discovery_classic_config.erl
index e5f41c9594..2183cda04d 100644
--- a/src/rabbit_peer_discovery_classic_config.erl
+++ b/src/rabbit_peer_discovery_classic_config.erl
@@ -37,7 +37,9 @@ list_nodes() ->
 -spec supports_registration() -> boolean().
 
 supports_registration() ->
-    false.
+    %% If we don't have any nodes configured, skip randomized delay and similar operations
+    %% as we don't want to delay startup for no reason. MK.
+    has_any_peer_nodes_configured().
 
 -spec register() -> ok.
 
@@ -63,3 +65,19 @@ lock(_Node) ->
 
 unlock(_Data) ->
     ok.
+
+%%
+%% Helpers
+%%
+
+has_any_peer_nodes_configured() ->
+    case application:get_env(rabbit, cluster_nodes, []) of
+        {[], _NodeType} ->
+            false;
+        {Nodes, _NodeType} when is_list(Nodes) ->
+            true;
+        [] ->
+            false;
+        Nodes when is_list(Nodes) ->
+            true
+    end.