Forwarding Port Traffic in Kubernete

Supposing you've migrated your services to kubernetes and there is a service with a hardcoded port 8755 from your legacy application listing some products in a JSON format a where the requirement declares the standard port is 80. To address this problem, you can use the ambassador design to export access to the service on port 80.

First of all, create a ConfigMap definition, pipe the configuration to haproxy.cfg and save it as my-service-ambassador-config.yml

apiVersion: v1
kind: ConfigMap
metadata:
   name: my-service-ambassador-config
data:
    haproxy.cfg: |-
        global
            daemon
            maxconn 256

        defaults
            mode http
            timeout connect 5000ms
            timeout client 50000ms
            timeout server 50000ms

        listen http-in
            bind *:80
            server server1 127.0.0.1:8775 maxconn 32

kubectl apply -f my-service-ambassador-config.yml

Create a pod definition called my-service.yml. As you can see, there is an ambassador container running the haproxy:1.7 image and proxying the incoming traffic on port 80 to the legacy service on port 8775.

apiVersion: v1
kind: Pod
metadata:
   name: my-service
spec:
    containers:
      - name: legacy-service
        image: legacy-service:1
      - name: haproxy-ambassador
        image: haproxy:1.7
        ports:
        - containerPort: 80
        - name: config-volume
          mountPath: /usr/local/etc/haproxy
    volumes:
      - name: config-volume
        configMap: 
          name: my-service-ambassador-config

kubectl apply -f my-service.yml

Let's test it by creating a busybox pod

apiVersion: v1
kind: Pod
metadata:
  name: busybox
spec:
  containers:
  - name: myapp-container
    image: radial/busyboxplus:curl
    command: ['sh', '-c', 'while true; do sleep 3600; done']

kubectl apply -f busybox.yml

The sub-command $(kubectl get pod my-service -o=custom-columns=IP:.status.podIP --no-headers) is used to get the IP address of my-service.

kubectl exec busybox -- curl $(kubectl get pod my-service -o=custom-columns=IP:.status.podIP --no-headers):80

For more about ambassador pattern, please check out Design patterns for container-based distributed systems