Merge pull request #11905 from rabbitmq/mergify/bp/v3.13.x/pr-11902

Classic peer discovery: node list warnings (backport #11898) (backport #11902)

Author: michaelklishin

deps/rabbit/src/rabbit_peer_discovery_classic_config.erl

@@ -23,8 +23,12 @@
 list_nodes() ->
     case application:get_env(rabbit, cluster_nodes, {[], disc}) of
         {Nodes, NodeType} ->
+            check_local_node(Nodes),
+            check_duplicates(Nodes),
             {ok, {add_this_node(Nodes), NodeType}};
         Nodes when is_list(Nodes) ->
+            check_local_node(Nodes),
+            check_duplicates(Nodes),
             {ok, {add_this_node(Nodes), disc}}
     end.
 
@@ -35,6 +39,26 @@ add_this_node(Nodes) ->
         false -> [ThisNode | Nodes]
     end.
 
+check_duplicates(Nodes) ->
+    case (length(lists:usort(Nodes)) == length(Nodes)) of
+        true ->
+            ok;
+        false ->
+            rabbit_log:warning("Classic peer discovery backend: list of "
+                               "nodes contains duplicates ~0tp",
+                               [Nodes])
+    end.
+
+check_local_node(Nodes) ->
+    case lists:member(node(), Nodes) of
+        true ->
+            ok;
+        false ->
+            rabbit_log:warning("Classic peer discovery backend: list of "
+                               "nodes does not contain the local node ~0tp",
+                               [Nodes])
+    end.
+
 -spec lock(Nodes :: [node()]) ->
     {ok, {{ResourceId :: string(), LockRequesterId :: node()}, Nodes :: [node()]}} |
     {error, Reason :: string()}.