I'm trying to make a server-client communication between pods in a K8s cluster using the python socket library.
When running outside of a cluster, the server-client connection works, however in the k8s the server doesn't even set up:
import socket
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("myApp", 30152)) # it breaks here
server_socket.listen()
And here are my configuration YAMLs:
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: myApp
labels:
app: myApp
spec:
replicas: 1
selector:
matchLabels:
app: myApp
template:
metadata:
labels:
app: myApp
spec:
containers:
- name: myApp
image: app_image:version
ports:
- containerPort: 30152
imagePullPolicy: Always
---
apiVersion: v1
kind: Service
metadata:
name: myApp
labels:
app: myApp
spec:
selector:
app: myApp
ports:
- name: myApp
protocol: TCP
port: 30152
type: ClusterIP
---
The service type is a ClusterIP as the connection would only be between pods in the same cluster. Does anyone know where the problem might come from?
CodePudding user response：
Here, I've build a little bit of an example with a client and a server python apps, talking to each other via k8s service. Almost from scratch (clone all the files from here if you want to follow along)
Server
server.py
import socket
import sys
import os
PORT = int(os.getenv('LISTEN_PORT'))
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_address = ('0.0.0.0', PORT)
print('Starting up on {} port {}'.format(*server_address))
sock.bind(server_address)
sock.listen()
while True:
print('\nWaiting for a connection')
connection, client_address = sock.accept()
try:
print('Connection from', client_address)
while True:
data = connection.recv(64)
print('Received {!r}'.format(data))
if data:
print('Sending data back to the client')
connection.sendall(data)
else:
print('No data from', client_address)
break
finally:
connection.close()
Dockerfile
FROM python:3-alpine
WORKDIR /app
COPY server.py .
CMD ["/usr/local/bin/python3", "/app/server.py"]
building an image, tagging, pushing to container repo (GCP):
docker build --no-cache -t q69936079-server .
docker tag q69936079-server gcr.io/<project_id>/q69936079-server
docker push gcr.io/<project_id>/q69936079-server
Client
client.py
import socket
import os
import sys
import time
counter = 0
SRV = os.getenv('SERVER_ADDRESS')
PORT = int(os.getenv('SERVER_PORT'))
while 1:
if counter != 0:
time.sleep(5)
counter = 1
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_address = (SRV, PORT)
print("Connection #{}".format(counter))
print('Connecting to {} port {}'.format(*server_address))
try:
sock.connect(server_address)
except Exception as e:
print("Cannot connect to the server,", e)
continue
try:
message = b'This is the message. It will be repeated.'
print('Sending: {!r}'.format(message))
sock.sendall(message)
amount_received = 0
amount_expected = len(message)
while amount_received < amount_expected:
data = sock.recv(64)
amount_received = len(data)
print('Received: {!r}'.format(data))
finally:
print('Closing socket\n')
sock.close()
Dockerfile
FROM python:3-alpine
WORKDIR /app
COPY client.py .
CMD ["/usr/local/bin/python3", "/app/client.py"]
building an image, tagging, pushing to container repo (GCP in my case):
docker build --no-cache -t q69936079-client .
docker tag q69936079-client gcr.io/<project_id>/q69936079-client
docker push gcr.io/<project_id>/q69936079-client
K8S
server deployment
apiVersion: apps/v1
kind: Deployment
metadata:
name: server-deployment
spec:
selector:
matchLabels:
app: server
replicas: 1
template:
metadata:
labels:
app: server
spec:
containers:
- name: server
image: "gcr.io/<project_id>/q69936079-server:latest"
env:
- name: PYTHONUNBUFFERED
value: "1"
- name: LISTEN_PORT
value: "30152"
client deployment
apiVersion: apps/v1
kind: Deployment
metadata:
name: client-deployment
spec:
selector:
matchLabels:
app: client
replicas: 1
template:
metadata:
labels:
app: client
spec:
containers:
- name: client
image: "gcr.io/<project_id>/q69936079-client:latest"
env:
- name: PYTHONUNBUFFERED
value: "1"
- name: SERVER_ADDRESS
value: my-server-service
- name: SERVER_PORT
value: "30152"
server service
apiVersion: v1
kind: Service
metadata:
name: my-server-service
spec:
type: ClusterIP
selector:
app: server
ports:
- protocol: TCP
port: 30152
Validation
k8s object
k get all
NAME READY STATUS RESTARTS AGE
pod/client-deployment-7dd5d675ff-pvwd4 1/1 Running 0 14m
pod/server-deployment-56bd44cc68-w6jns 1/1 Running 0 13m
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.140.0.1 <none> 443/TCP 12h
service/my-server-service ClusterIP 10.140.13.183 <none> 30152/TCP 38m
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/client-deployment 1/1 1 1 14m
deployment.apps/server-deployment 1/1 1 1 13m
NAME DESIRED CURRENT READY AGE
replicaset.apps/client-deployment-7dd5d675ff 1 1 1 14m
replicaset.apps/server-deployment-56bd44cc68 1 1 1 13m
Server logs
k logs -f deployment.apps/server-deployment
Starting up on 0.0.0.0 port 30152
Waiting for a connection
Connection from ('10.136.1.11', 48234)
Received b'This is the message. It will be repeated.'
Sending data back to the client
Received b''
No data from ('10.136.1.11', 48234)
Waiting for a connection
Connection from ('10.136.1.11', 48246)
Received b'This is the message. It will be repeated.'
Sending data back to the client
Received b''
No data from ('10.136.1.11', 48246)
Client logs
k logs -f deployment.apps/client-deployment
Connection #1
Connecting to my-server-service port 30152
Cannot connect to the server, [Errno 111] Connection refused
Connection #2
Connecting to my-server-service port 30152
Cannot connect to the server, [Errno 111] Connection refused
Connection #3
Connecting to my-server-service port 30152
Sending: b'This is the message. It will be repeated.'
Received: b'This is the message. It will be repeated.'
Closing socket
Connection #4
Connecting to my-server-service port 30152
Sending: b'This is the message. It will be repeated.'
Received: b'This is the message. It will be repeated.'
Closing socket