Today's highly data intensive applications requires us to use streams, and concurrency constructs, actors, streams and akka helps us with it. video here: https://youtu.be/cvXd7Y-e2-0

1. Actors, Akka,
Streams
ConceptsTomer Ben David

2. 1.Assume you know actors
theory
2.Become receive
3.Streams
4.Persistence
5.FSM
6.Remote
7.Cluster

3. become(blueState)
def blueState: Receive = { … }
def greenState: Receive = { … }
Define multiple receive functions
and become one of them

4. receive = greenReceive // => This is our default receive
Define default receive by
assigning it another receive

5. receive = greenReceive // => This is our default receive
Commands → Actor
Validate → Event

6. Commands → Actor
Validate → Event

7. Streams

8. Feed streams to actors
Fast big data
Can't look at it all
Ff we could we would all be
happy without streams

9. Reactive streams
Subscriber → Publisher: “Man I
have 5 empty slots in my buffer”
subscriber actually requests to
eat some messages

10. Source
.repeat("hh")
.throttle(rate)
.to(Sink)

11. Persistent Actors
(aka akka persistence)

12. don't loose internal actor state
upon crash

13. Class MyActor extends
PersistentActor

14. Only changes to actor are
persistent not the state like event
sourcing

15. command if validation succeeds
event is persisted to db

16. Only persisted events are
replayed as they can successfully
applied

17. Except for snapshot optimization

18. persist(MyEvent(MyOp))

19. If event successfully persisted we
update our actor state

20. Default persistency is journal to
filesystem

21. You can plug in persistency to
cassandra etc

22. Remember internal events are
stored not external commands

23. override def persistenceId = “my-
actor-class”

24. def receive - receives a command

25. def receiveRecover when getting
snapshot we override state
case snapshotAccount:

26. def receiveCommand // =>
1.Validate command
2.generate event
3.Persist event
4.Update State

27. class MyActor extends
PersistentFSM(State,
DomainEvent)
Types not values

28. override def applyEvent(evt:
DomainEvent, currentData: Data):
Data
We return the new data -
“updated”

29. PersistentFSM DSL
startsWith(Green)
when(Green) { case .. }

30. PersistentQuery
The read side of CQRS

31. PersistentQuery
Predefined query: Get All Events,
Get PersistentIds, Get Events by
PersistentId

32. Akka Remote, The basis of Akka
Cluster

33. "com.typesafe.akka" %% "akka-
remote" % "$akka.version$"

34. application.conf: provider from
local to remote, add hostname,
port..

35. Lookup or create a remote actor

36. Find an actor:
“akka.tcp://actorSystemName@
10.0.0.1:2552/user/actorName”

37. Lookup or create a remote actor

38. Akka cluster

39. Membership is peer to peer no
single point of failure

40. Leader and seeder, when node
joins leader marks it as up

41. Multiple nodes like 3 frontend 3
backend different roles all in
same cluster

42. preStart, postStop on member up
and unsubscribe

43. onReceive can check explicitly
role and decide what to do

44. What/Who would you like to
hear about? please do
comment, and if liked please
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