Stateful Application Server in JRuby

The talk includes an introduction to the problems that were solved by choosing a stateful applicaton server.

I will explain constraints, benefits and obvious differences to traditional database backed application servers.

Images taken from http://www.flickr.com/photos/x-ray_delta_one <3

Recording: http://media.eurucamp.org/#talk-2013-Overbryd

Transcript

1. stateful application server
2. Hi I’m Lukas @Overbryd
3. Working @Wooga
5. stateful application server
6. database based system
7. app app app load db clients
8. stateful system
9. app app app client
10. app app app dns load clients
11. every server is equal
12. app nginx jvm redis ssd
13. state
14. jvm {}
15. ‣ SessionManager ‣ Session ‣ Resources ‣ Items ‣ Quests ‣ Payments ...
16. the hard part
17. one place at a time
18. easy with one server, but how to scale out?
19. sharding!
20. “static sharding” shard = facebook_id % shards
22. raise Invalid, “wrong shard” unless Shard.valid?(facebook_id)
23. concurrency
24. jvm http threads sessions ticker thread worker threads
25. the hard part
26. serialized access to a session
27. easy for low contention like a single session
28. class Session attr_reader :lock def initialize @lock = Mutex.new end # ... end session.lock.synchronize do session.foo end
29. harder for high contention like the SessionManager
30. class SessionManager @current = ConcurrentHashMap.new def self.get(id) raise WrongShard unless Shard.valid?(id) unless session = @current.get(id) new_session = create(id) unless session = @current.put_if_absent(id, new_session) session = new_session end end session end end
31. t1 t2 {} S S
32. t1 t2 {} S S
33. t1 t2 {} S S session = @current.get(id) # => nil session = @current.get(id) # => nil
34. S2 t1 t2 {} S S
35. S2 t1 t2 {} S S S1 S2
36. S2 t1 t2 {} S S S1 S2 S2
37. S2 t1 t2 {} S S S1 S2 S2 S2
38. S2 t1 t2 {} S S S1 S2 S2 S2
39. S2 new_session = create(id) unless session = @current.put_if_absent(id, new_session) # => nil session = new_session # => #<Session:0x2> end t1 new_session = create(id) unless session = @current.put_if_absent(id, new_session) # => #<Session:0x2> t2 {} S S S1 S2 S2 S2
40. deployment
41. the hard part
42. one place at a time
43. handover
44. app nginx jvm1 jvm2 S1
45. app nginx jvm1 jvm2 S1
46. app nginx jvm1 jvm2 S1
47. app nginx jvm2 S1
48. global state
49. weird problem when handling sharded state
50. even weirder when every machine should be equal
51. app nginx jvm redis ssd
52. global data is kept local
53. populates via UPD broadcast
54. not “a huge” problem if stale
55. last write wins self healing
56. class Broadcast def self.spawn_listener Thread.new do socket = wait_until_socket_bind loop do if @stop_listener socket.close return end message, from = socket.recvfrom(1024) handle_message(message) end end end end
57. app jvm redis app jvm redis internal network jvm
58. app jvm redis app jvm redis internal network jvm
59. app jvm redis app jvm redis internal network jvm