Virtual Lines with Asyncio

PyConES2015 talk given by @igalarzab and @maraujop about how to build a virtual line software with Python 3.5, websockets, Redis and of course asyncio.

A virtual line is a software that allows people to wait in line for accessing an online resource, which can be anything we want to protect from high traffic spikes, such as a purchase process, or when we want people to access it in a specific order or controlled way.

Transcript

1. Virtual Lines
   
   with
   
   asyncIO
   Jose Ignacio Galarza
   
   @igalarzab
   Miguel Araujo
   
   @maraujop
   

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2. @ticketeaeng
   

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4. virtual line
   

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8. ticketea
   Why Python?
   ✤ Because we are not in the RubyCON :D
   ✤ Python 3 fixes some issues with concurrency
   ✤ This is a typical problem to be solved with async I/O
   ✤ Python scales without problems ;)
   

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9. ticketea
   Why asyncIO?
   ✤ This problem is I/O bound
   ✤ It’s bundled in the standard library
   ✤ It has a powerful community behind it
   ✤ One of the most readable concurrent paradigms in Python
   

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10. ticketea
    Why websockets?
    ✤ Two-ways communication between user and server
    ✤ We need almost real-time communication
    ✤ There is no-overhead in the payloads
    ✤ It’s possible to update from HTTP to Websocket
    ✤ Easy to pass through firewalls
    

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11. ticketea
    Why Redis?
    ✤ We need a cache to store counters atomically
    ✤ We don’t need a huge transactional engine
    ✤ It’s pretty fast
    ✤ It has a lot of libraries (also for asyncIO)
    

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12. how it
    
    works
    

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15. VLMn
    RESOURCE
    prepare_purchase with token signed
    access_resource
    pay
    leaves_resource
    CLIENTS_IN_RESOURCE++
    CLIENTS_IN_RESOURCE - 1
    

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16. show me
    
    the code
    

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17. ticketea
    New keywords
    async def name:
    await coro
    @asyncio.coroutine
    def name:
    yield from coro
    Python 3.4 Python 3.5
    

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18. ticketea
    HTTPServer
    class HTTPServer:
    def __init__(self, loop, host='127.0.0.1', port=8080)
    async def start(self)
    async def _start_http_server(self)
    async def _upgrade_to_websocket(self, request)
    async def _access_resource(self, request)
    async def _leave_resource(self, request)
    async def _config_resource(self, request)
    

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19. ticketea
    Where everything almost begins
    class HTTPServer:
    async def start(self):
    await self.redis.start()
    await self._start_http_server()
    async def _start_http_server(self):
    return await self.loop.create_server(
    self.app.make_handler(),
    self.host,
    self.port
    )
    

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20. ticketea
    Where everything begins
    if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    server = HTTPServer(loop, host, port)
    loop.run_until_complete(server.start())
    print('Listening to {0}:{1}'.format(host, port))
    try:
    loop.run_forever()
    except KeyboardInterrupt:
    loop.call_soon(loop.stop)
    print('Stopping server...')
    

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21. ticketea
    HTTPServer: From HTTP to Websocket
    async def _upgrade_to_websocket(self, request):
    websocket = web.WebSocketResponse()
    await websocket.prepare(request)
    resource_id = request.match_info.get('resource_id')
    vlm = await self._get_vlm(resource_id)
    ws_handler = WebsocketHandler(self.loop, websocket, vlm)
    await ws_handler.process_connection()
    

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22. ticketea
    VirtualLineManager
    class VirtualLineManager(object):
    def __init__(self, loop, redis, resource_id)
    async def init_resource(self)
    def start_updating_clients(self)
    async def keep_clients_updated(self)
    async def let_clients_pass(self)
    def add_connection(self, turn, handler)
    async def take_turn(self)
    

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23. ticketea
    VirtualLineManager
    async def init_resource(self):
    await self.redis.init_turn_granted_access(self.rid)
    await self.redis.init_clients_in_resource(self.rid)
    await self.redis.init_max_clients_in_resource(self.rid)
    def start_updating_clients(self):
    self.loop.create_task(self.keep_clients_updated())
    

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24. ticketea
    VirtualLineManager
    async def keep_clients_updated(self):
    await self.let_clients_pass()
    turn = await self.redis.get_turn_granted_access(self.resource_id)
    message = json.dumps({"granted_access": "true", "sig": ""})
    while self.conn_handlers:
    if int(self.conn_handlers[0]['turn']) <= int(turn):
    conn = self.conn_handlers.pop()
    conn['handler'].send_message(message)
    else:
    break
    message = json.dumps({'last_turn': turn})
    connections = deque()
    for conn_handler in self.conn_handlers:
    conn_handler['handler'].send_message(message)
    connections.append(conn_handler)
    self.conn_handlers = connections
    self.loop.call_later(
    self.UPDATE_INTERVAL, lambda: self.start_updating_clients())
    

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25. ticketea
    RedisHandler
    class RedisHandler:
    def __init__(self, host='127.0.0.1', port=6379, poolsize=10)
    async def start(self)
    async def access_resource(self, rid)
    async def leave_resource(self, rid)
    async def get_last_given_turn(self, rid)
    async def get_clients_in_resource(self, rid)
    async def init_clients_in_resource(self, rid)
    async def set_clients_in_resource(self, rid, clients)
    async def get_max_clients_in_resource(self, rid)
    async def init_max_clients_in_resource(self, rid)
    async def set_max_clients_in_resource(self, rid, max_clients)
    async def get_turn_granted_access(self, rid)
    async def init_turn_granted_access(self, rid)
    async def inc_turn_granted_access(self, rid, incr_quantity)
    async def take_turn(self, rid):
    return await self.redis.hincrby(rid, self.LAST_GIVEN_TURN, 1)
    

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26. CPU bound
    
    processes
    

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27. http://bit.ly/1MCDoKH
    

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29. DEMO TIME
    

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30. https://www.youtube.com/watch?v=7g0iBWKAvBQ
    

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31. ticketea
    questions?
    

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32. thanks!
    Jose Ignacio Galarza
    
    @igalarzab
    Miguel Araujo
    
    @maraujop
    

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