feat(stats): add `live_connections.{count,max}` stats to `emqx_stats`

src/emqx_cm.erl

@@ -92,6 +92,8 @@
          {?CHAN_CONN_TAB, 'connections.count', 'connections.max'}
         ]).
 
+-define(CONNECTED_CLIENT_STATS, {'live_connections.count', 'live_connections.max'}).
+
 %% Batch drain
 -define(BATCH_SIZE, 100000).
 
@@ -516,7 +518,8 @@ clean_down({ChanPid, ClientId}) ->
     do_unregister_channel({ClientId, ChanPid}).
 
 stats_fun() ->
-    lists:foreach(fun update_stats/1, ?CHAN_STATS).
+    lists:foreach(fun update_stats/1, ?CHAN_STATS),
+    update_connected_client_stats().
 
 update_stats({Tab, Stat, MaxStat}) ->
     case ets:info(Tab, size) of
@@ -524,6 +527,12 @@ update_stats({Tab, Stat, MaxStat}) ->
         Size -> emqx_stats:setstat(Stat, MaxStat, Size)
     end.
 
+update_connected_client_stats() ->
+    {CountStat, MaxStat} = ?CONNECTED_CLIENT_STATS,
+    CCCount = get_connected_client_count(),
+    emqx_stats:setstat(CountStat, MaxStat, CCCount),
+    ok.
+
 get_chann_conn_mod(ClientId, ChanPid) when node(ChanPid) == node() ->
     Chan = {ClientId, ChanPid},
     try [ConnMod] = ets:lookup_element(?CHAN_CONN_TAB, Chan, 2), ConnMod

src/emqx_stats.erl

@@ -21,6 +21,7 @@
 -include("emqx.hrl").
 -include("logger.hrl").
 -include("types.hrl").
+-include_lib("snabbkaffe/include/snabbkaffe.hrl").
 
 -logger_header("[Stats]").
 
@@ -67,8 +68,10 @@
 
 %% Connection stats
 -define(CONNECTION_STATS,
-        ['connections.count', %% Count of Concurrent Connections
-         'connections.max'    %% Maximum Number of Concurrent Connections
+        [ 'connections.count' %% Count of Concurrent Connections
+        , 'connections.max'   %% Maximum Number of Concurrent Connections
+        , 'live_connections.count' %% Count of connected clients
+        , 'live_connections.max' %% Maximum number of connected clients
         ]).
 
 %% Channel stats
@@ -216,6 +219,11 @@ handle_cast({setstat, Stat, MaxStat, Val}, State) ->
             ets:insert(?TAB, {MaxStat, Val})
     end,
     safe_update_element(Stat, Val),
+    ?tp(emqx_stats_setstat,
+        #{ count_stat => Stat
+         , max_stat => MaxStat
+         , value => Val
+         }),
     {noreply, State};
 
 handle_cast({update_interval, Update = #update{name = Name}},
@@ -274,4 +282,3 @@ safe_update_element(Key, Val) ->
         error:badarg ->
             ?LOG(warning, "Failed to update ~0p to ~0p", [Key, Val])
     end.
-

test/emqx_broker_SUITE.erl

@@ -364,6 +364,40 @@ t_connected_client_count_refresh({'end', Config}) ->
     {ok, _} = supervisor:restart_child(emqx_cm_sup, manager),
     ok.
 
+t_connected_client_stats({init, Config}) ->
+    ok = snabbkaffe:start_trace(),
+    Config;
+t_connected_client_stats(Config) when is_list(Config) ->
+    ?assertEqual(0, emqx_cm:get_connected_client_count()),
+    ?assertEqual(0, emqx_stats:getstat('live_connections.count')),
+    ?assertEqual(0, emqx_stats:getstat('live_connections.max')),
+    {ok, ConnPid} = emqtt:start_link([{clean_start, false}, {clientid, <<"clientid">>}]),
+    {{ok, _}, _} = wait_for_events(
+                     fun() -> emqtt:connect(ConnPid) end,
+                     [emqx_cm_connected_client_count_inc]
+                    ),
+    %% ensure stats are synchronized
+    wait_for_stats(
+      fun emqx_cm:stats_fun/0,
+      [#{count_stat => 'live_connections.count',
+         max_stat => 'live_connections.max'}]
+     ),
+    ?assertEqual(1, emqx_stats:getstat('live_connections.count')),
+    ?assertEqual(1, emqx_stats:getstat('live_connections.max')),
+    ok = emqtt:disconnect(ConnPid),
+    %% ensure stats are synchronized
+    wait_for_stats(
+      fun emqx_cm:stats_fun/0,
+      [#{count_stat => 'live_connections.count',
+         max_stat => 'live_connections.max'}]
+     ),
+    ?assertEqual(0, emqx_stats:getstat('live_connections.count')),
+    ?assertEqual(1, emqx_stats:getstat('live_connections.max')),
+    ok;
+t_connected_client_stats({'end', _Config}) ->
+    ok = snabbkaffe:stop(),
+    ok.
+
 wait_for_events(Action, Kinds) ->
     Predicate = fun(#{?snk_kind := K}) ->
                         lists:member(K, Kinds)
@@ -379,6 +413,27 @@ wait_for_events(Action, Kinds) ->
             {Res, {ok, Events}}
     end.
 
+wait_for_stats(Action, Stats) ->
+    Predicate = fun(Event = #{?snk_kind := emqx_stats_setstat}) ->
+                        Stat = maps:take(
+                                 [ count_stat
+                                 , max_stat
+                                 ], Event),
+                        lists:member(Stat, Stats);
+                   (_) ->
+                        false
+                end,
+    N = length(Stats),
+    Timeout = 100,
+    {ok, Sub} = snabbkaffe_collector:subscribe(Predicate, N, Timeout, 0),
+    Res = Action(),
+    case snabbkaffe_collector:receive_events(Sub) of
+        {timeout, []} ->
+            {Res, timeout};
+        {ok, Events} ->
+            {Res, {ok, Events}}
+    end.
+
 insert_fake_channels() ->
     %% Insert copies to simulate missed counts
     Tab = emqx_channel_info,