Some details about how Kubernetes Ingress Controller works

In this article I write down my steps to understand how the network traffic from Internet is passed through Ingress Controller.

I’ve been using Traefik as Ingress Controller in my Kubernetes cluster for a while. Thanks to the helpful articles here, and here, explaining the setup.

When I’m trying to get a understanding about how it works, this is a great article, especially this diagram.

A simplified diagram of my setup is like below:

As introduced here, there are 3 methods to expose the Ingress Controller (or a service) to Internet.

1. Use external LoadBalancer, for example, in this article. This method requires the cloud provider provides the LoadBalancer service.

spec:
  selector:
    k8s-app: traefik-ingress
  ports:
  - protocol: TCP
    port: 80
    name: http
  - protocol: TCP
    port: 443
    name: https
  type: LoadBalancer

2. Use NodePorts, for example, in this article. This method will expose a random port in range of 30000–32767 on the host running the pod. So to expose the Ingress Controller to Internet, another proxy is required to redirect the traffic.

spec:
  selector:
    k8s-app: traefik-ingress-lb
  ports:
    - protocol: TCP
      port: 80
      name: web
    - protocol: TCP
      port: 8080
      name: admin
  type: NodePort

3. Use HostPort, which is the way I’m following, from the traefik official guide.

    spec:
      containers:
      - image: traefik
        name: traefik-ingress-lb
        ports:
          - containerPort: 80
            hostPort: 80
          - containerPort: 443
            hostPort: 443
          - containerPort: 8080

I’m using this method because:

1. My cloud provider is a self-managed provider with great price and flexibility, but not so many customized services. “type: LoadBalancer” never works for me.
2. I created a single-master, many-workers cluster. I expect low network traffic. The Ingress Controller is deployed on the single master node. I point all DNS records for the (sub-)domain to the master node. It’s quite easy to setup.
3. A cluster with multiple…