fix(kafka_producer): fix message loss when kafka connection is down

lib-ee/emqx_ee_bridge/src/kafka/emqx_bridge_impl_kafka_producer.erl

@@ -176,10 +176,22 @@ on_kafka_ack(_Partition, _Offset, _Extra) ->
     %% Maybe need to bump some counters?
     ok.
 
-on_get_status(_InstId, #{client_id := ClientID}) ->
+on_get_status(_InstId, #{producers := Producers}) ->
-    case wolff:check_connectivity(ClientID) of
+    %% Just to pick some producer.
-        ok -> connected;
+    RandomVal = emqx_guid:gen(),
-        _ -> disconnected
+    FakeMsg = [#{key => RandomVal, value => RandomVal}],
+    %% Note: we must not check the connectivity to Kafka itself, but
+    %% only if there are producers available.  Otherwise, if Kafka
+    %% goes down, the resource will be considered down and messages
+    %% *will not* be sent to the wolff producers and buffered,
+    %% effectively losing the message as there are no buffer workers
+    %% for Kafka producer.
+    try wolff_producers:pick_producer(Producers, FakeMsg) of
+        {_Partition, _Pid} ->
+            connected
+    catch
+        error:{producer_down, _} ->
+            disconnected
     end.
 
 %% Parse comma separated host:port list into a [{Host,Port}] list