fix(telemetry): avoid hanging emqx_modules_app init with request

apps/emqx_modules/src/emqx_telemetry.erl

@@ -145,9 +145,13 @@ init(_Opts) ->
     {NodeUUID, ClusterUUID} = ensure_uuids(),
     {ok, State0#state{node_uuid = NodeUUID, cluster_uuid = ClusterUUID}}.
 
-handle_call(enable, _From, State0) ->
-    State = report_telemetry(State0),
-    {reply, ok, ensure_report_timer(State)};
+handle_call(enable, _From, State) ->
+    %% Wait a few moments before reporting the first telemetry, as the
+    %% apps might still be starting up.  Also, this avoids hanging
+    %% `emqx_modules_app' initialization in case the POST request
+    %% takes a lot of time.
+    FirstReportTimeoutMS = timer:seconds(10),
+    {reply, ok, ensure_report_timer(FirstReportTimeoutMS, State)};
 handle_call(disable, _From, State = #state{timer = Timer}) ->
     emqx_misc:cancel_timer(Timer),
     {reply, ok, State#state{timer = undefined}};
@@ -194,6 +198,9 @@ official_version(Version) ->
     match =:= re:run(Version, Pt, [{capture, none}]).
 
 ensure_report_timer(State = #state{report_interval = ReportInterval}) ->
+    ensure_report_timer(ReportInterval, State).
+
+ensure_report_timer(ReportInterval, State) ->
     State#state{timer = emqx_misc:start_timer(ReportInterval, time_to_report_telemetry_data)}.
 
 os_info() ->

apps/emqx_modules/test/emqx_telemetry_SUITE.erl

@@ -367,7 +367,15 @@ t_send_after_enable(_) ->
     ok = snabbkaffe:start_trace(),
     try
         ok = emqx_telemetry:enable(),
-        ?assertMatch({ok, _}, ?block_until(#{?snk_kind := telemetry_data_reported}, 2000, 100)),
+        Timeout = 12_000,
+        ?assertMatch(
+            {ok, _},
+            ?wait_async_action(
+                ok = emqx_telemetry:enable(),
+                #{?snk_kind := telemetry_data_reported},
+                Timeout
+            )
+        ),
         receive
             {request, post, _URL, _Headers, Body} ->
                 {ok, Decoded} = emqx_json:safe_decode(Body, [return_maps]),