Apache Flink eventTimeTimer does not trigger even time has passed - apache-flink

Question

Following this https://nightlies.apache.org/flink/flink-docs-master/api/java/org/apache/flink/streaming/api/TimerService.html, we are required to use the eventTimeTimer (currenttimestamp + 2 MIN) should trigger the onTimer event but it does not trigger. It only works when I use the processingTimeTimer.
My requirements is to create an alarm sink when an event came in after 2 mins or no event came in at all.
Here is my code:
#Override
public void processElement(AppEvent appEvent,
KeyedProcessFunction<UUID, AppEvent, KafkaAlert>.Context context,
Collector<KafkaAlert> collector) throws Exception {
AppEvent firstEvent = appEventValueState.value();
if (firstEvent == null) {
if (appEvent.getAppName().equals("My-APP")
&& appEvent.getStatus().equals("SENT")) {
//register this event
appEventValueState.update(appEvent);
long timer = app.getEventTimeMili() + 1000 * 60; // 1 MINUTE
context.timerService().registerEventTimeTimer(timer);
timerState.update(timer);
// System.out.println(timer);
}
}
}
#Override
public void onTimer(long timestamp,
KeyedProcessFunction<UUID, AppEvent, KafkaAlert>.OnTimerContext ctx,
Collector<KafkaAlert> out) throws Exception {
AppEvent appEventStateValue = appEventValueState.value();
KafkaAlert kafkaAlert = new KafkaAlert(appEventStateValue.getUuid(), appEventStateValue.getAppName());
out.collect(kafkaAlert);
cleanUp(ctx);
}
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
KafkaSource<String> kafkaSource = KafkaSource.<String>builder()
.setBootstrapServers(BOOTSTRAP_SERVER)
.setTopics("input-topic")
.setGroupId("my-kafka-group")
.setStartingOffsets(OffsetsInitializer.latest())
.setDeserializer(KafkaRecordDeserializationSchema.valueOnly(StringDeserializer.class))
.build();
DataStream<String> streamKafkaSource = env.fromSource(kafkaSource, WatermarkStrategy.forMonotonousTimestamps(),
"Kafka AppEvents");
DataStream<KafkaAlert> kafkaAlerts = streamKafkaSource.map(new AppEventMapperFunction())
.keyBy(AppEvent::getUuid)
.process(new AppEventKafkaFunction())
.name("AppEventKafka");
kafkaAlerts.addSink(new AlertSinkFunction())
.name("kafkaSink");
env.execute("Kakfa-AppEvent");
}

Answer 1

If an event-time timer isn't triggered, it's always because a large enough watermark never arrives.
There are several possible causes:
you haven't configured a watermark strategy
you haven't configured the watermark strategy to use idleness detection, and one or more sources is idle (or has no partitions from which to consume)
even if a watermark strategy does use idleness detection, if all of its sources become idle, then no watermarks will be emitted and the timer will never be triggered