Ordered messaging via multiple gen_rpc clients

src/emqx_broker.erl

@@ -256,7 +256,7 @@ aggre(Routes) ->
 -spec(forward(node(), emqx_types:topic(), emqx_types:delivery(), RPCMode::sync|async)
     -> emqx_types:deliver_result()).
 forward(Node, To, Delivery, async) ->
-    case emqx_rpc:cast(Node, ?BROKER, dispatch, [To, Delivery]) of
+    case emqx_rpc:cast(To, Node, ?BROKER, dispatch, [To, Delivery]) of
         true -> ok;
         {badrpc, Reason} ->
             ?LOG(error, "Ansync forward msg to ~s failed: ~p", [Node, Reason]),
@@ -264,7 +264,7 @@ forward(Node, To, Delivery, async) ->
     end;
 
 forward(Node, To, Delivery, sync) ->
-    case emqx_rpc:call(Node, ?BROKER, dispatch, [To, Delivery]) of
+    case emqx_rpc:call(To, Node, ?BROKER, dispatch, [To, Delivery]) of
         {badrpc, Reason} ->
             ?LOG(error, "Sync forward msg to ~s failed: ~p", [Node, Reason]),
             {error, badrpc};

src/emqx_rpc.erl

@@ -16,24 +16,41 @@
 -module(emqx_rpc).
 
 -export([ call/4
+        , call/5
         , cast/4
+        , cast/5
         , multicall/4
+        , multicall/5
         ]).
 
 -define(RPC, gen_rpc).
 
+-define(DefaultClientNum, 1).
+
 call(Node, Mod, Fun, Args) ->
     filter_result(?RPC:call(rpc_node(Node), Mod, Fun, Args)).
 
+call(Key, Node, Mod, Fun, Args) ->
+    filter_result(?RPC:call(rpc_node({Key, Node}), Mod, Fun, Args)).
+
 multicall(Nodes, Mod, Fun, Args) ->
     filter_result(?RPC:multicall(rpc_nodes(Nodes), Mod, Fun, Args)).
 
+multicall(Key, Nodes, Mod, Fun, Args) ->
+    filter_result(?RPC:multicall(rpc_nodes([{Key, Node} || Node <- Nodes]), Mod, Fun, Args)).
+
 cast(Node, Mod, Fun, Args) ->
     filter_result(?RPC:cast(rpc_node(Node), Mod, Fun, Args)).
 
-rpc_node(Node) ->
+cast(Key, Node, Mod, Fun, Args) ->
-    ClientNum = application:get_env(gen_rpc, tcp_client_num, 32),
+    filter_result(?RPC:cast(rpc_node({Key, Node}), Mod, Fun, Args)).
-    {Node, rand:uniform(ClientNum)}.
+
+rpc_node(Node) when is_atom(Node) ->
+    ClientNum = application:get_env(gen_rpc, tcp_client_num, ?DefaultClientNum),
+    {Node, rand:uniform(ClientNum)};
+rpc_node({Key, Node}) when is_atom(Node) ->
+    ClientNum = application:get_env(gen_rpc, tcp_client_num, ?DefaultClientNum),
+    {Node, erlang:phash2(Key, ClientNum) + 1}.
 
 rpc_nodes(Nodes) ->
     rpc_nodes(Nodes, []).
@@ -43,7 +60,6 @@ rpc_nodes([], Acc) ->
 rpc_nodes([Node | Nodes], Acc) ->
     rpc_nodes(Nodes, [rpc_node(Node) | Acc]).
 
-
 filter_result({Error, Reason})
   when Error =:= badrpc; Error =:= badtcp ->
     {badrpc, Reason};