fix: make rule cache update more reliable

apps/emqx_rule_engine/src/emqx_rule_registry.erl

@@ -75,6 +75,8 @@
 
 -export([ update_rules_cache/0
         , clear_rules_cache/0
+        , get_rules_from_cache/0
+        , update_rules_cache_locally/0
         ]).
 
 %% for debug purposes
@@ -465,30 +467,45 @@ delete_resource_type(Type) ->
 init([]) ->
     _TableId = ets:new(?KV_TAB, [named_table, set, public, {write_concurrency, true},
                                  {read_concurrency, true}]),
+    ok = ensure_table_subscribed(),
     {ok, #{}}.
 
 handle_call({add_rules, Rules}, _From, State) ->
     trans(fun lists:foreach/2, [fun insert_rule/1, Rules]),
-    _ = ?CLUSTER_CALL(update_rules_cache, []),
+    %% the multicall is necessary, because the other nodes maybe running an older emqx version
+    %% so the table has not been subscribed
+    update_rules_cache_on_all_nodes(),
     {reply, ok, State};
 
 handle_call({remove_rules, Rules}, _From, State) ->
     trans(fun lists:foreach/2, [fun delete_rule/1, Rules]),
-    _ = ?CLUSTER_CALL(update_rules_cache, []),
+    update_rules_cache_on_all_nodes(),
     {reply, ok, State};
 
 handle_call(Req, _From, State) ->
     ?LOG(error, "unexpected call - ~p", [Req]),
     {reply, ignored, State}.
 
 handle_cast(update_rules_cache, State) ->
-    _ = update_rules_cache(),
+    ok = ensure_table_subscribed(),
+    ok = update_rules_cache(),
     {noreply, State};
 
 handle_cast(Msg, State) ->
     ?LOG(error, "unexpected cast ~p", [Msg]),
     {noreply, State}.
 
+handle_info({mnesia_table_event, {write, _Tab, _NewRule, _OldRules, _Tid} = Event}, State) ->
+    ?LOG(debug, "mnesia_table_event: ~p~n", [Event]),
+    ok = update_rules_cache_locally(),
+    {noreply, State};
+
+handle_info({mnesia_table_event, {Delete, _Tab, _What, _OldRules, _Tid} = Event}, State)
+        when Delete =:= delete; Delete =:= delete_object ->
+    ?LOG(debug, "mnesia_table_event: ~p~n", [Event]),
+    ok = update_rules_cache_locally(),
+    {noreply, State};
+
 handle_info(Info, State) ->
     ?LOG(error, "unexpected info ~p", [Info]),
     {noreply, State}.
@@ -502,6 +519,20 @@ code_change(_OldVsn, State, _Extra) ->
 %%------------------------------------------------------------------------------
 %% Private functions
 %%------------------------------------------------------------------------------
+update_rules_cache_on_all_nodes() ->
+    ok = update_rules_cache(),
+    case ekka_mnesia:running_nodes() -- [node()] of
+        [] -> ok;
+        OtherNodes ->
+            _ = rpc:multicall(OtherNodes, ?MODULE, update_rules_cache_locally, [], 5000),
+            ok
+    end.
+
+ensure_table_subscribed() ->
+    case mnesia:subscribe({table, ?RULE_TAB, detailed}) of
+        {error, {already_exists, _}} -> ok;
+        {ok, _} -> ok
+    end.
 
 get_all_records(Tab) ->
     %mnesia:dirty_match_object(Tab, mnesia:table_info(Tab, wild_pattern)).