After more than one year of development, Wooga is heading for the global launch of its game "Kingsbridge"! This is the first game at Wooga with a backend written 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. Safely sharing state in a concurrent environment using JRuby Using Java concurrency utils in JRuby Sample problems solved, backed up with code Practical tips for capacity planning

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. appjvm redis appjvm redis
internal network
jvm

58. appjvm redis appjvm redis
internal network
jvm

59. appjvm redis appjvm redis
internal network
jvm