Problem

In our project, we want two pods working as server-client that communicate via the Python socket library. Both containers are built locally with docker build, pulled locally via imagePullPolicy: IfNotPresent on the yaml files and run on the same node of the k8s cluster (I'm running kubernetes vanilla, if that's important).

The communication works well when we

• run both python scripts in the command line
• run both scripts as containers using docker build and docker run
• the server app container is deployed in the K8s cluster and the client app is run either on the command line or as a docker container.

The communication fails when both server and client are deployed in K8s. kubectl logs client -f returns :

Traceback (most recent call last):
  File "client.py", line 7, in <module>
    client_socket.connect((IP_Server,PORT_Server))
TimeoutError: [Errno 110] Connection timed out

I suspect there's a problem with the outgoing request from the client script when it's deployed on the cluster, but I can't find where the problem lies.

Codes

server.py

import socket

IP = "0.0.0.0"
PORT = 1234

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server_socket.bind((IP, PORT))
server_socket.listen()

...

server.yaml

apiVersion: v1
kind: Service
metadata:
  name: server
  labels:
    app: server
spec:
  ports:
    - port: 1234
      targetPort: 1234
      protocol: TCP
  selector:
    app: server
---
apiVersion: v1
kind: Pod
metadata:
  name: server
  labels:
    app: server
spec:
  containers:
  - name: server
    image: server:latest
    imagePullPolicy: IfNotPresent
    ports:
    - containerPort: 1234

client.py

import socket

IP_Server = # the IP of the server service, obtained from "kubectl get svc" 
PORT_Server = 1234

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect((IP_Server,PORT_Server)) # fails here

...

client.yaml

apiVersion: v1
kind: Pod
metadata:
  name: client
  labels:
    app: client
spec:
  containers:
  - name: client
    image: client:latest
    imagePullPolicy: IfNotPresent