rabbit_feature_flags: Use cluster members hint for cluster sync (backport #8477) (backport #8479)

deps/rabbit/src/rabbit_feature_flags.erl

@@ -1822,10 +1822,19 @@ sync_feature_flags_with_cluster(Nodes, NodeIsVirgin) ->
 sync_feature_flags_with_cluster(Nodes, NodeIsVirgin, Timeout) ->
     Clustered = Nodes =/= [],
     case is_enabled(feature_flags_v2) of
-        true when Clustered    -> rabbit_ff_controller:sync_cluster();
-        true when NodeIsVirgin -> rabbit_ff_controller:enable_default();
-        true                   -> ok;
-        false                  -> sync_cluster_v1(Nodes, NodeIsVirgin, Timeout)
+        true when Clustered ->
+            %% We don't use `rabbit_nodes:filter_running()' here because the
+            %% given `Nodes' list may contain nodes which are not members yet
+            %% (the cluster could be being created or expanded).
+            Nodes1 = [N || N <- Nodes, rabbit:is_running(N)],
+            Nodes2 = lists:usort([node() | Nodes1]),
+            rabbit_ff_controller:sync_cluster(Nodes2);
+        true when NodeIsVirgin ->
+            rabbit_ff_controller:enable_default();
+        true ->
+            ok;
+        false ->
+            sync_cluster_v1(Nodes, NodeIsVirgin, Timeout)
     end.
 
 sync_cluster_v1([], NodeIsVirgin, _) ->
@@ -1930,7 +1939,12 @@ sync_cluster_v1(Nodes, _NodeIsVirgin, Timeout) ->
                "switching to controller's sync",
                [],
                #{domain => ?RMQLOG_DOMAIN_FEAT_FLAGS}),
-            rabbit_ff_controller:sync_cluster();
+            %% We don't use `rabbit_nodes:filter_running()' here because the
+            %% given `Nodes' list may contain nodes which are not members yet
+            %% (the cluster could be being created or expanded).
+            Nodes1 = [N || N <- Nodes, rabbit:is_running(N)],
+            Nodes2 = lists:usort([node() | Nodes1]),
+            rabbit_ff_controller:sync_cluster(Nodes2);
         false ->
             _ = verify_which_feature_flags_are_actually_enabled(),
             RemoteNodes = Nodes -- [node()],

deps/rabbit/src/rabbit_ff_controller.erl

@@ -35,7 +35,7 @@
          enable/1,
          enable_default/0,
          check_node_compatibility/1,
-         sync_cluster/0,
+         sync_cluster/1,
          refresh_after_app_load/0,
          get_forced_feature_flag_names/0]).
 
@@ -134,21 +134,21 @@ check_node_compatibility(RemoteNode) ->
     %% feature flags.
     check_node_compatibility_task(ThisNode, RemoteNode).
 
-sync_cluster() ->
+sync_cluster(Nodes) ->
     ?LOG_DEBUG(
        "Feature flags: SYNCING FEATURE FLAGS in cluster...",
        [],
        #{domain => ?RMQLOG_DOMAIN_FEAT_FLAGS}),
     case erlang:whereis(?LOCAL_NAME) of
         Pid when is_pid(Pid) ->
             %% The function is called while `rabbit' is running.
-            gen_statem:call(?LOCAL_NAME, sync_cluster);
+            gen_statem:call(?LOCAL_NAME, {sync_cluster, Nodes});
         undefined ->
             %% The function is called while `rabbit' is stopped. We need to
             %% start a one-off controller, again to make sure concurrent
             %% changes are blocked.
             {ok, Pid} = start_link(),
-            Ret = gen_statem:call(Pid, sync_cluster),
+            Ret = gen_statem:call(Pid, {sync_cluster, Nodes}),
             gen_statem:stop(Pid),
             Ret
     end.
@@ -273,8 +273,8 @@ proceed_with_task({enable, FeatureNames}) ->
     enable_task(FeatureNames);
 proceed_with_task(enable_default) ->
     enable_default_task();
-proceed_with_task(sync_cluster) ->
-    sync_cluster_task();
+proceed_with_task({sync_cluster, Nodes}) ->
+    sync_cluster_task(Nodes);
 proceed_with_task(refresh_after_app_load) ->
     refresh_after_app_load_task().
 
@@ -645,6 +645,15 @@ get_forced_feature_flag_names_from_config() ->
       Reason :: term().
 
 sync_cluster_task() ->
+    Nodes = running_nodes(),
+    sync_cluster_task(Nodes).
+
+-spec sync_cluster_task(Nodes) -> Ret when
+      Nodes :: [node()],
+      Ret :: ok | {error, Reason},
+      Reason :: term().
+
+sync_cluster_task(Nodes) ->
     %% We assume that a feature flag can only be enabled, not disabled.
     %% Therefore this synchronization searches for feature flags enabled on
     %% some nodes but not all, and make sure they are enabled everywhere.
@@ -657,7 +666,6 @@ sync_cluster_task() ->
     %% would make sure a feature flag isn't enabled while there is a network
     %% partition. On the other hand, this would require that all nodes are
     %% running before we can expand the cluster...
-    Nodes = running_nodes(),
     ?LOG_DEBUG(
        "Feature flags: synchronizing feature flags on nodes: ~p",
        [Nodes],

deps/rabbit/test/feature_flags_v2_SUITE.erl

@@ -202,6 +202,7 @@ setup_slave_node(Config, Testcase) ->
         _ ->
             ok = maybe_enable_feature_flags_v2(Config)
     end,
+    _ = catch rabbit_boot_state:set(ready),
     ok.
 
 setup_logger() ->