Connect Python app to Redis on Kubernetes cluster

Question

A docker container with a small Python app inside it is deployed to a Kubernetes cluster that has a redis master and a redis slave service running in the cluster. The Python app inside the Docker container is not able to connect to the redis across the cluster because the Python app is not configured properly to find redis on the network.

What specific changes need to be made to the code below in order for the Python app in app.py to be able to communicate successfully with the redis running in the same cluster?

PYTHON APP CODE

Here is app.py

from flask import Flask
from redis import Redis, RedisError
import os
import socket

# Connect to Redis
redis = Redis(host="redis", db=0, socket_connect_timeout=2, socket_timeout=2)

app = Flask(__name__)

@app.route("/")
def hello():
    try:
        visits = redis.incr("counter")
    except RedisError:
        visits = "<i>cannot connect to Redis, counter disabled</i>"

    html = "<h3>Hello {name}!</h3>" \
        "<b>Hostname:</b> {hostname}<br/>" \
        "<b>Visits:</b> {visits}"
    return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname(), visits=visits)

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80)

REDIS SERVICES IN THE SAME KUBERNETES CLUSTER

The redis master and redis slave running in the cluster are from public registries and are brought into the cluster by running kubectl apply -f with the following JSON:

Redis Master replication controller JSON from this link.
Redis Master service JSON from this link.
Redis Slave replication controller JSON from this link.
Redis Slave service JSON from this link.

mdaniel mdaniel · Accepted Answer · 2018-07-15T07:21:09

What specific changes need to be made to the code below in order for the python app in app.py to be able to communicate successfully with the redis running in the same cluster?

redis = Redis(host="redis-master", db=0, socket_connect_timeout=2, socket_timeout=2)

because the Service you installed is named redis-master, although that simple change I proposed above assumes that the flask app is running in the same kubernetes namespace as the redis-master Service. If that isn't true, you'll need to switch it to read:

redis = Redis(host="redis-master.whatever-namespace.svc.cluster.local",

and replace whatever-namespace with the actual, correct, namespace. If you don't remember or know, kubectl get --all-namespaces=true svc | grep redis-master will remind you.

Connect Python app to Redis on Kubernetes cluster

PYTHON APP CODE

1 Answers