ZeroMQ fails to .bind() on Docker on [0.0.0.0:5555] - address already in use. Why?

Question

Got a bit problem with ZeroMQ socket on trying to .bind() on 0.0.0.0:5555 address, when tried to run it in Docker container via a Rancher Cattle.

Every time I try to run it, I'm getting the same error:

zmq.error.ZMQError: Address already in use.

Tried to do EXPOSE 5555 and EXPOSE 5555/tcp in my Dockerfile, but it did not help me.

Here is a part of my code:

...
self.context = zmq.Context()
self.socket = self.context.socket(zmq.PUB)
self.socket.bind('tcp://%s:%d' % ('0.0.0.0', 5555))
...

Maybe somebody had the same problem. How to solve it?

Answer 1

ZeroMQ API defines 3-ways to go:

Assigning a local address to a socket

When assigning a local address to a socket using zmq_bind() with the tcp:// transport, the endpoint shall be interpreted as an interface followed by a colon and the TCP port number to use.

An interface may be specified by either of the following:
- The wild-card *, meaning all available interfaces.
- The primary IPv4 address assigned to the interface, in its numeric representation.
- The interface name as defined by the operating system.

Interface names are not standardised in any way and should be assumed to be arbitrary and platform dependent. On Win32 platforms no short interface names exist, thus only the primary IPv4 address may be used to specify an interface.

So, at least one ought make the job progress.

Answer 2

After two hours of debugging i tried to make .bind_to_random_port() and noticed, that my app in Docker starts via 4 Gunicorn workers. So after first worker started, three another workers can not bind to the same port. Be aware of binding to only one port while you have multiple threaded or multiple workers application.