Gunicorn, more than a WSGI server

Gunicorn is known as a Python WSGI HTTP Server for UNIX. But today the WSGI specification shows its limits and people wants more. This talk will introduce the new Gunicorn released in January with a new IPC library usable in others Python programs to handle the concurrency and support HTTP2.

Gunicorn handles the concurrency using a pre-fork worker model: workers are spawned processes managed by a main process. Until now there is no dialog between workers and the master which can trigger some issues like the thundering herd. To solve it and prepare gunicorn to support new protocols like HTTP2, a new IPC library has been specifically written in pure python. Mostly inspired from imsg in OpenBSD (but also Mojo), this new library is entirely written in Python and can be used outside of Gunicorn.

This talk will present the following:

1) The design of Gunicorn 1, its pros and cons 2) Description of the new IPC library how you can use it in your own projects 3) The design of Gunicorn 2 and its usage of the new IPC library, how it can do more than simply WSGI and HTTP 1.1.

Transcript

1. MORE THAN A WSGI SERVER
   Python FOSDEM 2016
   

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2. WHAT
   IS GUNICORN
   

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3. A WSGI SERVER
   ▸ PEP 3333
   ▸ pre-fork worker model
   ▸ Python > 2.6x
   ▸ handle Django & Paste configuration
   ▸ support any concurrency framework
   

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4. ADDITIONS TO WSGI
   ▸ ALREADY_HANDLED: take control of the socket
   ▸ ‘gunicorn.socket’ environ
   ▸ ‘gunicorn.raw_uri’ environ
   ▸ `transfer-encoding: chunked`
   

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5. PREFORK WORKER MODEL
   ARBITER
   WORKER
   WORKER
   share socket
   WORKER
   listen
   handle signals
   supervise
   accept
   WSGI server
   handle signals
   

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6. SHARE NOTHING
   ▸ share only file descriptors
   ▸ Privilege separation
   ▸ Worker: simple process with a run function
   

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7. WORKER
   accept loop
   setup signals
   sockets
   configuration
   log
   parent pid
   tempfile
   class MyWorker(WorkerBase):
   def __init__(..):
   …
   def init_process(self):
   …
   def run(self):
   …
   

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8. LET IT CRASH
   ▸ run the application
   ▸ need to notify the arbiter
   ▸ tempfile updates
   ▸ handle application errors
   ▸ but should crash on errors most of the time
   

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9. set application
   set Config
   EMBED
   class MyApp(BaseApplication):
   def load_config(self):
   …
   def load(self):
   …

   return self.application
   

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10. DO MORE
    >
    

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11. DO MORE. BE SAFER.
    ▸ improve listening in the sync worker
    ▸ remove the tempfile
    ▸ prepare for the new protocols
    ▸ improve logging
    ▸ going further
    

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12. ACCEPT WHEN NEEDED
    ▸ place the listening sockets in an event loop
    ▸ on read, start to accept
    ▸ also have a timer
    

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13. IMPORT
    GUNICORN.IMSG
    

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14. GUNICORN.IMSG
    ▸ communicate between processes
    ▸ use UNIX socket
    ▸ sendmsg/recvmsg + buffer
    ▸ 2 methods: send, receive
    ▸ zero copy memory
    

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15. child
    parent
    IMSG EXAMPLE
    fds =socket.socketpair()
    pid = os.fork()
    if pid != 0:
    # parent
    socket.close(fds[1])
    imsg = IMSG(fds[0]
    return main(imsg)
    # child
    socket.close(fds[0])
    var imsg = IMSG(fds[1])
    return main(imsg)
    

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16. wait for a message
    send a message
    IMSG EXAMPLE
    main(imsg):
    imsg.send(“sometype”, “somemsg”),
    dispatch_msg(imsg)
    dispatch_msg(imsg):
    while True:
    msg = imsg.recv()
    if msg is None:
    sleep(1)
    continue
    print(msg.data)
    

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17. REMOVING TEMPFILE
    ▸ a socket pair is opened for each workers
    ▸ an imsg object is created for each
    ▸ imsg object are placed in an eventloop to read
    asynchronously
    ▸ maybe extracted from the code as a simple lib
    

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18. DETACHED MODE
    ▸ rework ALREADY_HANDLED
    ▸ socket control is given to app
    ▸ but still supervised
    ▸ simple API
    

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19. simple proc abstraction
    return a proc instance
    EXAMPLE
    def app(environ, start_response):
    ..

    start_response(status, headers)
    proc = MyProc(environ)
    return proc
    class MyProc(gunicorn.Proc):
    def status(self):
    return STATUS_ALIVE
    def terminate(self, Reason):
    ….
    

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20. IMPROVE LOGGING
    ▸ logging will now be handled in its own process
    ▸ log infos passed via imsg and dispatched by the arbiter
    ▸ fix privilege separation issues
    

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21. GOING FURTHER
    ▸ HTTP 2
    ▸ static file server?
    ▸ fastcgi?
    

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23. HTTP://GUNICORN.ORG
    Gunicorn
    HTTP://ENKIM.EU
    Enki Multimedia
    

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