kubernetes pod talking to a localhost port

Question

I have a celery instance running inside a pod in local kubernetes cluster whereas the redis server/broker it connects to is started on my localhost:6379 without kubernetes . How can i get my k8 pod to talk to locally deployed redis?

Answer 1

You can create a Headless Service and an Endpoint with statically defined IP address of the node where the redis server is running.

---

I've created an example to illustrate you how it works.

First, I created a Headless Service and an Endpoint.
NOTE: Endpoint has the IP address of the node where redis server is running:

# example.yml
---
apiVersion: v1
kind: Service
metadata:
  name: redis
  namespace: default
spec:
  clusterIP: None
  ports:
  - name: redis
    port: 6379
    protocol: TCP
---
apiVersion: v1
kind: Endpoints
metadata:
  name: redis
  namespace: default
subsets:
  - addresses:
      - ip: 10.156.0.58 # your node's IP address
    ports:
      - port: 6379
        name: redis
        protocol: TCP

After creating above resources, we are able to resolve the redis service name to the IP address:

# kubectl get svc,ep redis
NAME            TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
service/redis   ClusterIP   None         <none>        6379/TCP   28m

NAME              ENDPOINTS          AGE
endpoints/redis   10.156.0.58:6379   28m

# kubectl run dnsutils --image=gcr.io/kubernetes-e2e-test-images/dnsutils:1.3 -it --rm
/ # nslookup redis
Server:         10.96.0.10
Address:        10.96.0.10#53

Name:   redis.default.svc.cluster.local
Address: 10.156.0.58

Additionally, if your redis server is only listening on localhost, you need to modify the iptables rules. To configure port forwarding from port 6379 (default redis port) to localhost you can use:
NOTE: Instead of 10.156.0.58 use the IP address of the node where your redis server is running.

# iptables -t nat -A PREROUTING -p tcp -d 10.156.0.58 --dport 6379 -j DNAT --to-destination 127.0.0.1:6379

As you can see, it is easier if redis is listening not only on the localhost, as we don't have to modify the iptables rules then.

Finally, let's see if we can connect from Pod to the redis server on the host machine:

# kubectl exec -it redis-client -- bash
root@redis-client:/# redis-cli -h redis
redis:6379> SET key1 "value1"
OK