Slides from the Akka Streams session on VJUG24 2016-09-27.

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
Special thanks

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
Process

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

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

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

12. akka streams
Not only linear streams
Source
SinkProcess
Source
Sink
Process Process

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 (JVM and JavaScript) as well as network
protocols
http://www.reactive-streams.org

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

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

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

17. 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<String>> sink =
Sink.foreach(str -> System.out.println(str));
RunnableGraph<NotUsed> runnable =
source.via(flow).to(sink);
runnable.run(materializer);

18. Akka Streams in 20 seconds:
CompletionStage<Done> done =
Source.single(42)
.map(n -> n.toString())
.runForeach(System.out::println, 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. Materialization
Gears from GeeCON.org,(it’s an awesome conf)

22. What is “materialization” really?

23. What is “materialization” really?

24. What is “materialization” really?

25. What is “materialization” really?

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

27. 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

28. 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

29. Alpakka – a community for Stream connectors
Demo

30. Alpakka – a community for Stream connectors
Demo

31. Akka Streams & HTTP
streams
& HTTP

32. Streaming in Akka HTTP
http://doc.akka.io/docs/akka/2.4.7/scala/stream/stream-customize.html#graphstage-scala
“Framed entity streaming” https://github.com/akka/akka/pull/20778
HttpServer as a:
Flow[HttpRequest, HttpResponse]

33. Streaming in Akka HTTP
http://doc.akka.io/docs/akka/2.4.7/scala/stream/stream-customize.html#graphstage-scala
“Framed entity streaming” https://github.com/akka/akka/pull/20778
HttpServer as a:
Flow[HttpRequest, HttpResponse]
HTTP Entity as a:
Source[ByteString, _]

34. Streaming from Akka HTTP

35. Streaming from Akka HTTP

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

37. 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

38. Thanks for listening!
@apnylle
blog.akka.io
markatta.com/codemonkey
johan.andren@lightbend.com
Sample sources
https://github.com/johanandren/akka-stream-samples/tree/vjug24