Python ConnectionRefusedError: [Errno 111] Connection refused on Docker container

Question

I have a simple Python script, that creates a Docker container of choice, and then creates a TCP tunnel that forwards requests to it. I use sockets within Python to forward the data sent in between the client and Docker container.

My piece of code that is not working:

# open socket to container
socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socket.connect((socket.gethostbyname('container IP - e.g. 172.17.0.2'), 2222))

I tried this part of the code also like this: socket.connect(('172.17.0.2', 2222)) and like it is shown in the code example. Only difference is that in my real code, I have the IP pulled from the container like so:

import docker
_DOCKER_CLIENT = docker.from_env()
c = _DOCKER_CLIENT.containers.run(
    image='linuxserver/openssh-server:latest',
    auto_remove=True,
    detach=True
)

# wait for container to start
cc = _DOCKER_CLIENT.containers.get(c.id)

# get container IP address
ip = cc.attrs['NetworkSettings']['IPAddress']

Error I get when I try to connect to the Docker container from the socket in Python:

ConnectionRefusedError: [Errno 111] Connection refused

Then, I tried to do the same thing from the Python cli in a standard shell, so I launched this in bash:

~$ python3
>>> import socket
>>> socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
>>> socket.connect(('172.17.0.2', 2222))

----- no issues up until this point -----

>>> buffer = socket.recv(0x400)
>>> print(buffer)
SSH-2.0-OpenSSH_8.3

>>> quit()

As you can see, I can do this without issues in bash, but, when I launch the Python script as the same user, I get the Connection refused error.

The routing table is also correct:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         _gateway        0.0.0.0         UG    600    0        0 wlp0s20f3
link-local      0.0.0.0         255.255.0.0     U     1000   0        0 virbr1
172.17.0.0      0.0.0.0         255.255.0.0     U     0      0        0 docker0
172.18.0.0      0.0.0.0         255.255.0.0     U     0      0        0 br-7ee23b92049c
192.168.0.0     0.0.0.0         255.255.255.0   U     600    0        0 wlp0s20f3
192.168.33.0    0.0.0.0         255.255.255.0   U     0      0        0 virbr2
192.168.100.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr1
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0

I can also ping the container without issues.

Anyone, can you please spot the issue? Is Python working differently in cli mode than in standard interpreting mode in a script?

Answer 1

So. I have mitigated the issue. The problem lied in me not waiting for the service inside of the container to fully boot and bind to a port.

I needed to add a waiting loop that checks whether the container's service is ready and then connect the socket.

I created a class that is used as a waiter, that gradually increases the timeout. After each sleep cycle, I check again, if I can connect to the socket.

Now it all works flawlessly.