kubernetes pod talking to a localhost port - kubectl

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