refactor(clustering/rpc): dp does not need concentrator

kong/clustering/rpc/manager.lua

@@ -5,7 +5,6 @@ local _MT = { __index = _M, }
 local server = require("resty.websocket.server")
 local client = require("resty.websocket.client")
 local socket = require("kong.clustering.rpc.socket")
-local concentrator = require("kong.clustering.rpc.concentrator")
 local future = require("kong.clustering.rpc.future")
 local utils = require("kong.clustering.rpc.utils")
 local callbacks = require("kong.clustering.rpc.callbacks")
@@ -42,15 +41,17 @@ function _M.new(conf, node_id)
     -- clients[node_id]: { socket1 => true, socket2 => true, ... }
     clients = {},
     client_capabilities = {},
-    client_ips = {},  -- store DP node's ip addr
     node_id = node_id,
     conf = conf,
     cluster_cert = assert(clustering_tls.get_cluster_cert(conf)),
     cluster_cert_key = assert(clustering_tls.get_cluster_cert_key(conf)),
     callbacks = callbacks.new(),
   }
 
-  self.concentrator = concentrator.new(self, kong.db)
+  if conf.role == "control_plane" then
+    self.concentrator = require("kong.clustering.rpc.concentrator").new(self, kong.db)
+    self.client_ips = {},  -- store DP node's ip addr
+  end
 
   return setmetatable(self, _MT)
 end
@@ -59,7 +60,10 @@ end
 function _M:_add_socket(socket, capabilities_list)
   local sockets = self.clients[socket.node_id]
   if not sockets then
-    assert(self.concentrator:_enqueue_subscribe(socket.node_id))
+    if self.concentrator then
+      assert(self.concentrator:_enqueue_subscribe(socket.node_id))
+    end
+
     sockets = setmetatable({}, { __mode = "k", })
     self.clients[socket.node_id] = sockets
   end
@@ -87,7 +91,10 @@ function _M:_remove_socket(socket)
     self.clients[node_id] = nil
     self.client_ips[node_id] = nil
     self.client_capabilities[node_id] = nil
-    assert(self.concentrator:_enqueue_unsubscribe(node_id))
+
+    if self.concentrator then
+      assert(self.concentrator:_enqueue_unsubscribe(node_id))
+    end
   end
 end