This document summarizes a presentation about Akka streams, which is a toolkit for building highly concurrent, distributed, and resilient message-driven applications on the JVM. It provides asynchronous back pressured stream processing using sources, sinks, and flows. Key features include actors for concurrency, clustering for location transparency and resilience, and integration with technologies like Kafka, Cassandra and HTTP. The document outlines how Akka streams work, how to write stream applications, and how streams can be used for scenarios like HTTP requests/responses and streaming data. It encourages contributions to Akka and discusses next steps like improved remoting and more stream connectors.

1. akka streams
Reactive Integrations with
that just work™
Johan Andrén
Konrad Malawski

2. Johan Andrén
Akka Team
Stockholm Scala User Group

3. Konrad `ktoso` Malawski
Akka Team,
Reactive Streams TCK,
Persistence, HTTP

4. Make building powerful concurrent &
distributed applications simple.
Akka is a toolkit and runtime
for building highly concurrent,
distributed, and resilient
message-driven applications
on the JVM

5. Actors – simple & high performance concurrency
Cluster / Remoting – location transparency, resilience
Cluster tools – and more prepackaged patterns
Streams – back-pressured stream processing
Persistence – Event Sourcing
HTTP – complete, fully async and reactive HTTP Server
Official Kafka, Cassandra, DynamoDB integrations, tons
more in the community
Complete Java & Scala APIs for all features
What’s in the toolkit?

7. “Stream”
has many meanings

8. akka streams
Asynchronous back pressured stream processing
Source Sink
Flow

9. akka streams
Asynchronous back pressured stream processing
Source Sink
(possible)
asynchronous
boundaries
Flow

10. akka streams
Asynchronous back pressured stream processing
Source Sink
10 msg/s 1 msg/s
OutOfMemoryError!!
Flow

11. akka streams
Asynchronous back pressured stream processing
Source Sink
10 msg/s 1 msg/s
hand me 3 morehand me 3 more
1 msg/s Flow

12. akka streams
Not only linear streams
Source
SinkFlow
Source
Sink
Flow
Flow

13. Reactive Streams
Reactive Streams is an initiative to provide a standard for
asynchronous stream processing with non-blocking back
pressure. This encompasses efforts aimed at runtime
environments as well as network protocols
http://www.reactive-streams.org

14. Part of JDK 9
java.util.concurrent.Flow

15. Reactive Streams
RS Library A RS library B
async
boundary

16. Reactive Streams
RS Library A RS library B
async
boundary
Make building powerful concurrent &
distributed applications simple.

17. The API
Akka Streams
Complete and awesome
Java and Scala APIs
(Just like everything in Akka)

18. Akka Streams in 20 seconds:
Source<Integer, NotUsed> source = null;
Flow<Integer, String, NotUsed> flow =
Flow.<Integer>create().map((Integer n) -> n.toString());
Sink<String, CompletionStage<Done>> sink =
Sink.foreach(str -> System.out.println(str));
RunnableGraph<NotUsed> runnable =
source.via(flow).to(sink);
runnable.run(materializer);

19. Akka Streams in 20 seconds:
CompletionStage<String> firstString =
Source.single(1)
.map(n -> n.toString())
.runWith(Sink.head(), materializer);

20. Source.single(1).map(i -> i.toString).runWith(Sink.head())
// types: _
Source<Int, NotUsed>
Flow<Int, String, NotUsed>
Sink<String, CompletionStage<String>>
Akka Streams in 20 seconds:

21. Source.single(1).map(i -> i.toString).runWith(Sink.head())
// types: _
Source<Int, NotUsed>
Flow<Int, String, NotUsed>
Sink<String, CompletionStage<String>>
Akka Streams in 20 seconds:

22. Materialization
Gears from GeeCON.org,(it’s an awesome conf)

23. What is “materialization” really?

24. What is “materialization” really?

25. What is “materialization” really?

26. What is “materialization” really?

27. What is “materialization” really?
Check out the
“Implementing an akka-streams materializer for big data”
talk later today.

28. AlpakkaA community for Streams connectors
http://blog.akka.io/integrations/2016/08/23/intro-alpakka

29. Alpakka – a community for Stream connectors
Threading & Concurrency in Akka Streams Explained (part I)
Mastering GraphStages (part I, Introduction)
Akka Streams Integration, codename Alpakka
A gentle introduction to building Sinks and Sources using GraphStage APIs
(Mastering GraphStages, Part II)
Writing Akka Streams Connectors for existing APIs
Flow control at the boundary of Akka Streams and a data provider
Akka Streams Kafka 0.11

30. Alpakka – a community for Stream connectors
Existing examples:
MQTT
AMQP
Streaming HTTP
Streaming TCP
Streaming FileIO
Cassandra Queries
“Reactive Kafka” (akka-stream-kafka)
S3, SQS & other Amazon APIs
Streaming JSON
Streaming XML
…

31. Alpakka – a community for Stream connectors
Demo

32. Alpakka – a community for Stream connectors
Demo

33. Akka Streams & HTTP
streams
& HTTP

34. A core feature not obvious to the untrained eye…!
Akka Streams / HTTP
Quiz time!
TCP is a ______ protocol?

35. A core feature not obvious to the untrained eye…!
Akka Streams / HTTP
Quiz time!
TCP is a STREAMING protocol!

36. Streaming in Akka HTTP
http://doc.akka.io/docs/akka/2.4/scala/stream/stream-customize.html#graphstage-scala
“Framed entity streaming”
http://doc.akka.io/docs/akka/2.4/java/http/routing-dsl/source-streaming-support.html
HttpServer as a:
Flow[HttpRequest, HttpResponse]

37. Streaming in Akka HTTP
HttpServer as a:
Flow[HttpRequest, HttpResponse]
HTTP Entity as a:
Source[ByteString, _]
http://doc.akka.io/docs/akka/2.4/scala/stream/stream-customize.html#graphstage-scala
“Framed entity streaming”
http://doc.akka.io/docs/akka/2.4/java/http/routing-dsl/source-streaming-support.html

38. Streaming in Akka HTTP
HttpServer as a:
Flow[HttpRequest, HttpResponse]
HTTP Entity as a:
Source[ByteString, _]
Websocket connection as a:
Flow[ws.Message, ws.Message]
http://doc.akka.io/docs/akka/2.4/scala/stream/stream-customize.html#graphstage-scala
“Framed entity streaming”
http://doc.akka.io/docs/akka/2.4/java/http/routing-dsl/source-streaming-support.html

39. It’s turtles buffers all the way down!
xkcd.com

40. Streaming from Akka HTTP

41. Streaming from Akka HTTP

42. Streaming from Akka HTTP
No demand from TCP
=
No demand upstream
=
Source won’t generate tweets
=>
Bounded memory
stream processing!
Demo

43. Streaming from Akka HTTP (Java)
public static void main(String[] args) {
final ActorSystem system = ActorSystem.create();
final Materializer materializer = ActorMaterializer.create(system);
final Http http = Http.get(system);
final Source<Tweet, NotUsed> tweets = Source.repeat(new Tweet("Hello world"));
final Route tweetsRoute =
path("tweets", () ->
completeWithSource(tweets, Jackson.marshaller(), EntityStreamingSupport.json())
);
final Flow<HttpRequest, HttpResponse, NotUsed> handler =
tweetsRoute.flow(system, materializer);
http.bindAndHandle(handler,
ConnectHttp.toHost("localhost", 8080),
materializer
);
System.out.println("Running at http://localhost:8080");
}

44. Streaming from Akka HTTP (Java)
public static void main(String[] args) {
final ActorSystem system = ActorSystem.create();
final Materializer materializer = ActorMaterializer.create(system);
final Http http = Http.get(system);
final Source<Tweet, NotUsed> tweets = Source.repeat(new Tweet("Hello world"));
final Route tweetsRoute =
path("tweets", () ->
completeWithSource(tweets, Jackson.marshaller(), EntityStreamingSupport.json())
);
final Flow<HttpRequest, HttpResponse, NotUsed> handler =
tweetsRoute.flow(system, materializer);
http.bindAndHandle(handler,
ConnectHttp.toHost("localhost", 8080),
materializer
);
System.out.println("Running at http://localhost:8080");
}

45. Streaming from Akka HTTP (Scala)
object Example extends App
with SprayJsonSupport with DefaultJsonProtocol {
import akka.http.scaladsl.server.Directives._
implicit val system = ActorSystem()
implicit val mat = ActorMaterializer()
implicit val jsonRenderingMode = EntityStreamingSupport.json()
implicit val TweetFormat = jsonFormat1(Tweet)
def tweetsStreamRoutes =
path("tweets") {
complete {
Source.repeat(Tweet(""))
}
}
Http().bindAndHandle(tweetsStreamRoutes, "127.0.0.1", 8080)
System.out.println("Running at http://localhost:8080");
}

46. Next steps for Akka
Completely new Akka Remoting (goal: 700.000+ msg/s (!)),
(it is built using Akka Streams, Aeron).
More integrations for Akka Streams stages, project Alpakka.
Reactive Kafka polishing with SoftwareMill, Krzysiek Ciesielski
Akka Typed progressing again, likely towards 3.0.
Akka HTTP 2.0 Proof of Concept in progress.
Collaboration with Reactive Sockets

47. Ready to adopt on prod?

48. Totally, go for it.

49. Akka <3 contributions
Easy to contribute tickets:
https://github.com/akka/akka/issues?q=is%3Aissue+is%3Aopen+label%3Aeasy-to-contribute
https://github.com/akka/akka/issues?q=is%3Aissue+is%3Aopen+label%3A%22nice-to-have+%28low-prio%29%22
Akka Stream Contrib
https://github.com/akka/akka-stream-contrib
Mailing list:
https://groups.google.com/group/akka-user
Public chat rooms:
http://gitter.im/akka/dev developing Akka
http://gitter.im/akka/akka using Akka

50. Reactive Platform
Reactive Platform
Reactive Platform

51. Further reading:
Reactive Streams: reactive-streams.org
Akka documentation: akka.io/docs
Free O’Reilly report – very out soon.
Example Sources:
ktoso/akka-streams-alpakka-talk-demos-2016
Get involved:
sources: github.com/akka/akka
mailing list: akka-user @ google groups
gitter channel: https://gitter.im/akka/akka
Contact:
Konrad ktoso@lightbend.com Malawski
http://kto.so / @ktosopl

52. Thanks!
Questions?
@apnylle johan.andren@lightbend.com
@ktosopl konrad.malawski@lightbend.com