Akka-streams (specifically the ActorMaterializer implementation of streams) yields single-VM, ephemeral implementations of graphs. Multi-VM/multi-restart message persistence is orthogonal to its design and goals. You can use additional features of Akka (PersistentActors, DData, Akka clusters and cluster sharding) to implement "eventually processed at least once" behavior, but you'll need to employ more than just akka-streams to do it. You'll need to add message persistence features in yourself.
Brian Maso On Thu, Jan 17, 2019 at 10:08 PM adgang <v.adity...@gmail.com> wrote: > This is a post(set of questions really) regarding the implications of > at-most-once(maybe-once) delivery reliability offered by akka actors on > APIs and software based on akka. From my understanding, even messages sent > by actors to self can be lost. > > Till now, I have been in scenarios where delivery guarantee is not > necessary so life was good. But now, I need reliability from my service at > least to the extent that a subscriber should know that a message has been > lost. > 1. If messages can be lost in actor system, and akka-streams are based on > actors, does that mean akka-streams are leaky? Thats pretty scary to think > about. Specifically does a Flow(or GraphStage) ensure that stream entities > are not lost? > For example, is the below code(based on Source.single doc > <https://doc.akka.io/docs/akka/2.5/stream/operators/Source/single.html>) > guaranteed to print `[hello]`? > import akka.stream.*; > > CompletionStage<List<String>> future = Source.single("hello").runWith( > Sink.seq(), materializer); > CompletableFuture<List<String>> completableFuture = future. > toCompletableFuture(); > completableFuture.thenAccept(result -> System.out.println(result)); > > 2. If messages can be lost in actor system, and akka-http is based on > actors, does that mean akka-http APIs, lets say websocket API randomly > drops messages. > For example, in: > http.singleWebSocketRequest(WebSocketRequest.create("wss:// > api.example.com"), flow, mat) > > is it at least guaranteed that my flow will reliably receive > everything on the websocket in order? > 3. In actor world, I would have a sequence number on each message and let > the receiver actor take remedial measures on a lost(probably never because > of at-most-once reliability issues so far) sequence number. In case we live > in a dystopian world where the answers to 1. and 2. are yes, this wouldn't > work because the external web service I consume does not implement sequence > numbers. Because any sequence number I generate within the application will > only add sequence numbers to messages that are not already lost. Is this a > correct understanding? > > -- > > ***************************************************************************************************** > ** New discussion forum: https://discuss.akka.io/ replacing akka-user > google-group soon. > ** This group will soon be put into read-only mode, and replaced by > discuss.akka.io > ** More details: > https://akka.io/blog/news/2018/03/13/discuss.akka.io-announced > > ***************************************************************************************************** > >>>>>>>>>> > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to akka-user+unsubscr...@googlegroups.com. > To post to this group, send email to akka-user@googlegroups.com. > Visit this group at https://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > -- ***************************************************************************************************** ** New discussion forum: https://discuss.akka.io/ replacing akka-user google-group soon. ** This group will soon be put into read-only mode, and replaced by discuss.akka.io ** More details: https://akka.io/blog/news/2018/03/13/discuss.akka.io-announced ***************************************************************************************************** >>>>>>>>>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. To unsubscribe from this group and stop receiving emails from it, send an email to akka-user+unsubscr...@googlegroups.com. To post to this group, send email to akka-user@googlegroups.com. Visit this group at https://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
