Disallow removal of the last stream member

deps/rabbit/src/rabbit_stream_coordinator.erl

@@ -341,26 +341,31 @@ apply(#{index := _Idx} = Meta0, {_CmdTag, StreamId, #{}} = Cmd,
                monitors = Monitors0} = State0) ->
     Stream0 = maps:get(StreamId, Streams0, undefined),
     Meta = maps:without([term, machine_version], Meta0),
-    Stream1 = update_stream(Meta, Cmd, Stream0),
-    Reply = case Stream1 of
-                #stream{reply_to = undefined} ->
-                    ok;
+    case filter_command(Meta, Cmd, Stream0) of
+        ok ->
+            Stream1 = update_stream(Meta, Cmd, Stream0),
+            Reply = case Stream1 of
+                        #stream{reply_to = undefined} ->
+                            ok;
+                        _ ->
+                            %% reply_to is set so we'll reply later
+                            '$ra_no_reply'
+                    end,
+            case Stream1 of
+                undefined ->
+                    return(Meta, State0#?MODULE{streams = maps:remove(StreamId, Streams0)},
+                           Reply, []);
                 _ ->
-                    %% reply_to is set so we'll reply later
-                    '$ra_no_reply'
-            end,
-    case Stream1 of
-        undefined ->
-            return(Meta, State0#?MODULE{streams = maps:remove(StreamId, Streams0)},
-                   Reply, []);
-        _ ->
-            {Stream2, Effects0} = evaluate_stream(Meta, Stream1, []),
-            {Stream3, Effects1} = eval_listeners(Stream2, Effects0),
-            {Stream, Effects2} = eval_retention(Meta, Stream3, Effects1),
-            {Monitors, Effects} = ensure_monitors(Stream, Monitors0, Effects2),
-            return(Meta,
-                   State0#?MODULE{streams = Streams0#{StreamId => Stream},
-                                  monitors = Monitors}, Reply, Effects)
+                    {Stream2, Effects0} = evaluate_stream(Meta, Stream1, []),
+                    {Stream3, Effects1} = eval_listeners(Stream2, Effects0),
+                    {Stream, Effects2} = eval_retention(Meta, Stream3, Effects1),
+                    {Monitors, Effects} = ensure_monitors(Stream, Monitors0, Effects2),
+                    return(Meta,
+                           State0#?MODULE{streams = Streams0#{StreamId => Stream},
+                                          monitors = Monitors}, Reply, Effects)
+            end;
+        Reply ->
+            return(Meta, State0, Reply, [])
     end;
 apply(Meta, {down, Pid, Reason} = Cmd,
       #?MODULE{streams = Streams0,
@@ -874,6 +879,23 @@ make_ra_conf(Node, Nodes) ->
       machine => {module, ?MODULE, #{}},
       ra_event_formatter => Formatter}.
 
+filter_command(_Meta, {delete_replica, _, #{node := Node}}, #stream{members = Members0}) ->
+    Members = maps:filter(fun(_, #member{target = S}) when S =/= deleted ->
+                                  true;
+                             (_, _) ->
+                                  false
+                          end, Members0),
+    case maps:size(Members) =< 1 of
+        true ->
+            rabbit_log:warning(
+              "~s failed to delete ~p replica, last cluster member",
+              [?MODULE, Node]),
+            {error, last_stream_member};
+        false ->
+            ok
+    end;
+filter_command(_, _, _) ->
+    ok.
 
 update_stream(Meta, Cmd, Stream) ->
     try
@@ -1536,6 +1558,7 @@ set_running_to_stopped(Members) ->
                  (_, M) ->
                      M
              end, Members).
+
 -ifdef(TEST).
 -include_lib("eunit/include/eunit.hrl").
 -endif.

deps/rabbit/test/rabbit_stream_queue_SUITE.erl

@@ -53,6 +53,7 @@ groups() ->
            leader_failover_dedupe,
            add_replicas]},
      {cluster_size_3_parallel, [parallel], [delete_replica,
+                                            delete_last_replica,
                                             delete_classic_replica,
                                             delete_quorum_replica,
                                             consume_from_replica,
@@ -444,6 +445,30 @@ delete_replica(Config) ->
     check_leader_and_replicas(Config, [Server0]),
     rabbit_ct_broker_helpers:rpc(Config, 0, ?MODULE, delete_testcase_queue, [Q]).
 
+delete_last_replica(Config) ->
+    [Server0, Server1, Server2] =
+        rabbit_ct_broker_helpers:get_node_configs(Config, nodename),
+    Ch = rabbit_ct_client_helpers:open_channel(Config, Server0),
+    Q = ?config(queue_name, Config),
+    ?assertEqual({'queue.declare_ok', Q, 0, 0},
+                 declare(Ch, Q, [{<<"x-queue-type">>, longstr, <<"stream">>}])),
+    check_leader_and_replicas(Config, [Server0, Server1, Server2]),
+    ?assertEqual(ok,
+                 rpc:call(Server0, rabbit_stream_queue, delete_replica,
+                          [<<"/">>, Q, Server1])),
+    ?assertEqual(ok,
+                 rpc:call(Server0, rabbit_stream_queue, delete_replica,
+                          [<<"/">>, Q, Server2])),
+    %% check they're gone
+    check_leader_and_replicas(Config, [Server0]),
+    %% delete the last one
+    ?assertEqual({error, last_stream_member},
+                 rpc:call(Server0, rabbit_stream_queue, delete_replica,
+                          [<<"/">>, Q, Server0])),
+    %% It's still here
+    check_leader_and_replicas(Config, [Server0]),
+    rabbit_ct_broker_helpers:rpc(Config, 0, ?MODULE, delete_testcase_queue, [Q]).
+
 grow_coordinator_cluster(Config) ->
     [Server0, Server1, _Server2] =
         rabbit_ct_broker_helpers:get_node_configs(Config, nodename),