Stateful Application Server in JRuby

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stateful application server

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Hi I’m Lukas @Overbryd

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Working @Wooga

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stateful application server

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database based system

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app app app load db clients

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stateful system

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app app app client

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app app app dns load clients

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every server is equal

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app nginx jvm redis ssd

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state

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jvm {}

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‣ SessionManager ‣ Session ‣ Resources ‣ Items ‣ Quests ‣ Payments ...

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the hard part

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one place at a time

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easy with one server, but how to scale out?

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sharding!

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“static sharding” shard = facebook_id % shards

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raise Invalid, “wrong shard” unless Shard.valid?(facebook_id)

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concurrency

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jvm http threads sessions ticker thread worker threads

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the hard part

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serialized access to a session

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easy for low contention like a single session

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class Session attr_reader :lock def initialize @lock = Mutex.new end # ... end session.lock.synchronize do session.foo end

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harder for high contention like the SessionManager

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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

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t1 t2 {} S S

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t1 t2 {} S S

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t1 t2 {} S S session = @current.get(id) # => nil session = @current.get(id) # => nil

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S2 t1 t2 {} S S

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S2 t1 t2 {} S S S1 S2

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S2 t1 t2 {} S S S1 S2 S2

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S2 t1 t2 {} S S S1 S2 S2 S2

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S2 t1 t2 {} S S S1 S2 S2 S2

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S2 new_session = create(id) unless session = @current.put_if_absent(id, new_session) # => nil session = new_session # => # end t1 new_session = create(id) unless session = @current.put_if_absent(id, new_session) # => # t2 {} S S S1 S2 S2 S2

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deployment

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the hard part

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one place at a time

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handover

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app nginx jvm1 jvm2 S1

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app nginx jvm1 jvm2 S1

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app nginx jvm1 jvm2 S1

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app nginx jvm2 S1

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global state

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weird problem when handling sharded state

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even weirder when every machine should be equal

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app nginx jvm redis ssd

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global data is kept local

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populates via UPD broadcast

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not “a huge” problem if stale

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last write wins self healing

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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