Expose TCP traffic examples

After istio is installed, follow these steps:

0. Label the default namespace for istio sidecar injection

kubectl label namespace default istio-injection=enabled --overwrite

1. Patch istio-ingressgateway service so that the new port is supported.

Create a file named patch-service.yaml with the following content:

spec:
  ports:
  - name: tcp-31400
    protocol: TCP
    port: 31400
    targetPort: 31400

Run the following command

kubectl -n istio-system patch service istio-ingressgateway --patch "$(cat patch-service.yaml)"  

2. Create deployment, service, gateway and virtual service

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world-deployment
spec:
  selector:
    matchLabels:
      greeting: hello
      department: world
  replicas: 1
  template:
    metadata:
      labels:
        greeting: hello
        department: world
    spec:
      containers:
      - name: hello
        image: "email4tong/pathecho:latest"
        imagePullPolicy: Always
---
apiVersion: v1
kind: Service
metadata:
  name: hello-world
spec:
  selector:
    greeting: hello
    department: world
  ports:
  - protocol: TCP
    port: 7000
    targetPort: 8080
---
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: tcp-echo-gateway
spec:
  selector:
    istio: ingressgateway
  servers:
  - port:
      number: 31400
      name: tcp
      protocol: TCP
    hosts:
    - "*"
---
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: tcp-echo
spec:
  hosts:
  - "*"
  gateways:
  - tcp-echo-gateway
  tcp:
  - match:
    - port: 31400
    route:
    - destination:
        host: hello-world.default.svc.cluster.local
        port:
          number: 7000

3. Now use the istio-ingressgateway service external endpoint (IP or hostname) and port 31400 to access the service. In above example, it is a simple http echo, so use curl to test is fine. If the actual service is not http but using any other tcp protocols, then you cannot use curl to test