Channels: development issue with multiple daphne workers

[Zhiyu (Drew) Li]

Hi there,

I am trying to migrate a tornado project to django channel2. I have moved all essential parts and wired them up in channel. It runs OK in development mode, but in production it seems the multi-daphne worker configuration is causing strange errors.

AttributeError: '_UnixSelectorEventLoop' object has no attribute 'remove_timeout' 

 

I followed instructions on the official doc (https://channels.readthedocs.io/en/latest/deploying.html) to set up supervisor and nginx. But I am still lack of understanding how it works. Cloud you please explain more on the following settings?

# TCP socket used by Nginx backend upstream

socket=tcp://localhost:8000

# Each process needs to have a separate socket file, so we use process_num

# Make sure to update "mysite.asgi" to match your project name

command=daphne -u /run/daphne/daphne%(process_num)d.sock --fd 0 --access-log - --proxy-headers mysite.asgi:application

# Number of processes to startup, roughly the number of CPUs you have

numprocs=4

Questions:

What is "--fd 0" here? Is "0" the file descriptor for socket  "tcp://localhost:8000" that Nginx is proxying to?

What is "-u /run/daphne/daphne%(process_num)d.sock" then? Why do we need to set up separate socket for each daphne process? Are all the daphne processes already talking to "fd 0"?

My website only works if I change either of the following

A) change to numprocs=1 ;

Or

B) remove "-u /run/daphne/daphne%(process_num)d.sock"

Thanks

Drew

[Andrew Godwin]

I'm not sure why you're getting the  _UnixSelectorEventLoop - that sounds like a Twisted error you should search around for, and make sure you have the right package versions.

--fd 0 should not be needed in that command line, since you're already passing the UNIX socket, I don't remember why it's there.

I suggest you remove fd=0 and see if that then works with multiple processes.

Andrew

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[Zhiyu/Drew Li]

Thanks Andrew,

I tried removing "--fd 0" but it didnt work. I got 504 time out error no matter numprocs=1 or 4.

Do you know are there any open-source projects that use channel2?  I just want to take a look at their repos as my examples.

Thanks

Drew

[Fogmoon]

Hi Drew,

Do you now totally understand the parameters -u(bind to unix socket) together with --fd(bind to file descriptor) in the command line configure? The document https://channels.readthedocs.io/en/latest/deploying.html has not been updated since you post this question.

I also feel confused about why here use these two binding endpoint together, although I know daphne support it :

# daphne/cli.py

# Build endpoint description strings from (optional) cli arguments

endpoints = build_endpoint_description_strings(

    host=args.host,

    port=args.port,

    unix_socket=args.unix_socket,

    file_descriptor=args.file_descriptor,

)

endpoints = sorted(args.socket_strings + endpoints)

# daphne/server.py

for socket_description in self.endpoints:

    logger.info("Configuring endpoint %s", socket_description)

    ep = serverFromString(reactor, str(socket_description))

    listener = ep.listen(self.http_factory)

    listener.addCallback(self.listen_success)

    listener.addErrback(self.listen_error)

    self.listeners.append(listener)

So, the key point is in which scenario we need to bind multiple endpoints.  I can not find any document about binding multiple endpoints. If @Andrew can give some suggestion or reference will be great appreciate.

在 2018年11月27日星期二 UTC+8上午7:10:13，Zhiyu (Drew) Li写道：