Akka Streams recreate stream in case of stage failure - scala

Question

I have very simple Akka Streams flow which reads msg from Kafka using alpakka, performs some manipulation on msg and indexes it to Elasticsearch.
I'm using CommitableSource, therefore i'm in At-Least-Once strategy. I commit my offset only when index to ES succeed, if it fails I will read again the message because form latest known offset.
val decider: Supervision.Decider = {
case _:Throwable => Supervision.Restart
case _ => Supervision.Restart
}
val config: Config = context.system.settings.config.getConfig("akka.kafka.consumer")
val flow: Flow[CommittableMessage[String, String], Done, NotUsed] =
Flow[CommittableMessage[String,String]].
map(msg => Event(msg.committableOffset,Success(Json.parse(msg.record.value()))))
.mapAsync(10) { event => indexEvent(event.json.get).map(f=> event.copy(json = f))}
.mapAsync(10)(f => {
f.json match {
case Success(_)=> f.committableOffset.commitScaladsl()
case Failure(ex) => throw new StreamFailedException(ex.getMessage,ex)
}
})
val r: Flow[CommittableMessage[String, String], Done, NotUsed] = RestartFlow.onFailuresWithBackoff(
minBackoff = 3.seconds,
maxBackoff = 3.seconds,
randomFactor = 0.2, // adds 20% "noise" to vary the intervals slightly
maxRestarts = 20 // limits the amount of restarts to 20
)(() => {
println("Creating flow")
flow
})
val consumerSettings: ConsumerSettings[String, String] =
ConsumerSettings(config, new StringDeserializer, new StringDeserializer)
.withBootstrapServers("localhost:9092")
.withGroupId("group1")
.withProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest")
val restartSource: Source[CommittableMessage[String, String], NotUsed] = RestartSource.withBackoff(
minBackoff = 3.seconds,
maxBackoff = 30.seconds,
randomFactor = 0.2, // adds 20% "noise" to vary the intervals slightly
maxRestarts = 20 // limits the amount of restarts to 20
) {() =>
Consumer.committableSource(consumerSettings, Subscriptions.topics("test"))
}
implicit val mat: ActorMaterializer = ActorMaterializer(ActorMaterializerSettings(context.system).withSupervisionStrategy(decider))
restartSource
.via(flow)
.toMat(Sink.ignore)(Keep.both).run()
What I would like to achieve, is to restart entire flow Source -> Flow-> Sink. If from any reason I was no able to index message in Elastic.
I tried the following:
Supervision.Decider - It looks like flow was recreated but no
message was pulled from Kafka, obviously because it remembers it
offset.
RestartSource - doesn't looks ether, because exception happens in flow stage.
RestartFlow - Doesn't help as well because it restarts only Flow, but I need to restart Source from last successful offset.
Is there any elegant way to do that?

Answer 1

You can combine restartable source, flow & sink. Nobody prevents you from doing restartable source/flow/sink for each part of the graph
Update:
code example
val sourceFactory = () => Source(1 to 10).via(Flow.fromFunction(x => { println("problematic flow"); x }))
RestartSource.withBackoff(4.seconds, 4.seconds, 0.2)(sourceFactory)