This document discusses using Akka actors and Redis for building a scalable chat server architecture. Key points include: 1) Using Akka actors for the chat room, user, and supervisor actors to handle chat logic and failures in a distributed, asynchronous manner. 2) Storing chat room membership and messages in Redis for real-time updates between actors using pub/sub. 3) The Lettuce client is used to handle connections to the Redis cluster for features like master/slave failover and periodic topology refreshes.

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Go Hagiwara (Oklahomer) , Dev3 Center

2. ● Oklahomer
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● @ LINE
● LINE LIVE API
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● Bot Framework
ChatOps bot
● Java/Golang/Python/Perl

3. ● LINE
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4. ● MC
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LIVE

5. ●
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7. WebSocket - Server-Client
akka actor model - Server
Redis Cluster - Pub/Sub Server
KVS

8. subtitle
TITLE

9. WebSocket

10. akka Actor Model

11. Pub/sub Server
Lua scripting atomic
Redis Cluster

12. WebSocket - Server-Client
akka actor model - Server
Redis Cluster - Server

13. akka Actor Model

14. ● Perl
● Java
● Effective Java
● Java
● Java
●

15. ● Parallel::Prefork
● Parallel::ForkManager
● java.util.concurrent package
● ParallelStream
Perl v.s. Java

17. akka Actor Model
● actor
● actor
●
● Actor
●
●
● actor
●

19. Actor

20. Actor
● Actor mailbox
● mailbox
● mailbox
●
● Actor
● actor mailbox
●
●

22. ● Actor
●
●

23. Supervisor

24. Supervisor
● actor actor
●
● actor actor
● let-it-crash
actor “crash”
●

25. Supervisor Strategy
● actor
●
● crash actor
●

26. Supervisor Strategy -
● One-for-One strategy
● crash actor
● All-for-One strategy
● actor
● actor actor
actor

27. Supervisor Strategy - Directives
● Restart - actor
mailbox
● Crash actor actor restart
●
● preRestart hook
→
● Resume - mailbox
●

28. Supervisor Strategy - Directives
● Stop - actor
●
● actor
● Escalate - Supervisor Actor
● Supervisor Strategy
Child Actor → Parent Actor → Grandparent Actor

29. Supervisor Strategy - Directives

30. Supervisor Strategy -
1 public class MyActor extends UntypedActor {
2 private static SupervisorStrategy strategy =
3 new OneForOneStrategy(10, Duration.create("1 minute"), t -> {
4 if (t instanceof ActorInitializationException) {
5 return stop();
6 } else if (t instanceof ActorKilledException) {
7 return stop();
8 } else if (t instanceof Exception) {
9 return restart();
10 }
11
12 return escalate();
13 });
14
15 @Override
16 public SupervisorStrategy supervisorStrategy() {
17 return strategy;
18 }
19
20 @Override
21 public void onReceive(Object o) throws Exception {
22 }
23 }

31. Actor

32. Actor
● Actor ActorRef
●
●
●
● etc…
● actor dead
letter
●

33. Actor
●
● watch actor
● Terminated
● unwatch
●
● Actor crash actor

34. Chat Server Actor

36. ChatSupervisor
● 1 JVM 1
● actor
● ” ”
actor
●

37. ChatRoomActor
●
●
● Redis pub/sub
● UserActor
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● UserActor
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38. UserActor
●
● WebSocket
● ChatRoomActor
●

39. ● ChatRoomActor UserActor ChatSupervisor
● ” ” UserActor
ChatRoomActor
● WebSocket UserActor
● ChatRoomActor crash → restart UserActor restart
● ChatRoomActor UserActor

40. ● ChatRoomActor UserActor
● ChatRoomActor UserActor watch
● UserActor WebSocket UserActor stop
● ChatRoomActor Terminated
● ChatRoomMembers
●
● Watch Terminated
● ChatRoomActor restart
● ChatRoomActor crash UserActor

41. ●
● Restart
1 public static Props props(final AggregatedChannel channel,
2 final ChatRoom chatRoom,
3 final ChatRoomMembers chatRoomMembers) {
4 // Returns a property to construct ChatRoomActor
5 // NOTE: Those objects passed to actor's constructor are inherited on restart
6 // such as ChatRoomMembers that caches belonging UserActors
7 return Props.create(ChatRoomActor.class,
8 () -> new ChatRoomActor(channel,
9 chatRoom,
10 chatRoomMembers));
11 }

42. ● actor
● actor
● actor Actor System
●
● Actor model

43. ● Controller
● validate
● ChatSupervisor ChatRoomActor
● WebSocket
● WebSocket UserActor
● ChatRoomActor
WebSocket

44. ● Controller / UserActor WebSocket
●
● UserActor crash
● Supervisor Strategy restart
resume
● Validation
●
● UserActor

45. ●
● Redis
● WebSocket
●
● actor
●

46. - Blocking API
● WebSocket Jetty issue
● https://github.com/eclipse/jetty.project/issues/272
● UserActor
●
●
● JVM
● Spring API
● Jetty issue

47. - Blocking API
● ThreadPool
● Jetty issue
● Watchdog
●
●
● UserActor
● ChatRoomActor Terminated
Actor

49. ●
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51. ●
● Redis Cluster pub/sub
● key ChatRoomActor pub/sub
● ChatRoomActor UserActor

52. ● Remote Actor
● WebSocket UserActor
● ChatRoomActor
ChatSupervisor, UserActor
● Deploy Redis pub/sub

53. Redis
● Actor Redis Pub/
Sub
● Pub/Sub
● Subscribe
●
● Actor

54. Lettuce
● Redis Cluster
● Master/slave failover MOVED/ASK node
● API
● Pub/sub subscribe failover
● Lua scripting

55. Lettuce
●
● Redis Cluster reshard
validation
● Redis Cluster → application
● Failover reshard
● Periodic refresh
● Adaptive refresh

56. Lettuce
1 /*
2 To get rid of stale connection and establish new connection when crush/failover occurs,
3 refresh its topologyView periodically.
4 */
5 ClusterTopologyRefreshOptions topologyRefreshOptions =
6 ClusterTopologyRefreshOptions.builder()
7 .enablePeriodicRefresh(30, TimeUnit.SECONDS)
8 .enableAllAdaptiveRefreshTriggers()
9 .build();
10 /*
11 Basically we use the default settings, but to avoid connection error caused by newly added
server,
12 override the validateClusterNodeMembership and skip validation for new server.
13 */
14 ClusterClientOptions clusterClientOptions =
15 ClusterClientOptions.builder()
16 .validateClusterNodeMembership(false)
17 .topologyRefreshOptions(topologyRefreshOptions)
18 .build();

57. ● WebSocket
● Server - Client
● akka Actor Model
●
● Actor Actor
● Blocking API
● Redis Cluster
●
●

58. ● LINE LIVE
●
● https://engineering.linecorp.com/ja/blog/detail/85
● Yet another Akka introduction for dummies
●
● http://blog.oklahome.net/2016/01/akka-introduction-for-dummies.html
● How to cook lettuce @Java casual
● Lettuce
● https://www.slideshare.net/Oklahomer/how-to-cook-lettuce-java-
casual

59. THANK YOU