Kubernetes - Service, Ingress

tags: Kubernetes

Foreword

In the Kubernetes cluster, we want to connect to the Pod we can use the “port-forward” to achieve the port forwarding. However, we have many Pods need to connect. We can use the Service to connect.

Service

Definition

An abstract way to expose an application running on a set of Pods as a network service. Every Pod get its own IP address, however in Deployment the Pod may be create or delete. The IP address of Pod will be changed.

Type of Service

• ClusterIP Exposes the Service on a cluster-internal IP. Choosing this value makes the Service only reachable from within the cluster. This is the default ServiceType.
• NodePort Exposes the Service on each Node's IP at a static port. You'll be able to contact the NodePort Service, from outside the cluster, by requesting <NodeIP>:<NodePort>.
• Loadbalancer If your Kubernetes Cluster is installed on Amazon or Google Cloud Platform. We can use the Loadbalancer from cloud provider. Exposes the Service externally using a cloud provider's load balancer.

Practice

If we want to create a service on k8s we need to create a deployment first.

kubectl apply -f demo-deployment.yml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: blue-nginx
spec:
  replicas: 2
  template:
    metadata:
      labels:
        app: blue-nginx
    spec:
      containers:
        - name: nginx
          image: hcwxd/blue-whale
          ports:
            - containerPort: 3000
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: purple-nginx
spec:
  replicas: 2
  template:
    metadata:
      labels:
        app: purple-nginx
    spec:
      containers:
        - name: nginx
          image: hcwxd/purple-whale
          ports:
            - containerPort: 3000

Then use kubectl expose deploy blue-nginx --type=NodePort --name=my-deployment-service to create Service.

We also can use the yaml file to create Service.

apiVersion: v1
kind: Service
metadata:
  name: blue-service
spec:
  type: NodePort
  selector:
    app: blue-nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000
      NodePort: 3003
---
apiVersion: v1
kind: Service
metadata:
  name: purple-service
spec:
  type: NodePort
  selector:
    app: purple-nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 3000
      NodePort: 3002

• Type is NodePort
• mtargetPort -> the port of container allow to connect
• port -> the targetPort of Pod mapping to the Cluster IP of Service
• nodePort -> the targetPort of Pod mapping to the IP of Node
• selector -> select which Pod we want to expose

Now we can use <Node IP>:<Node Port> to connect the Pod.

Ingress

Definition

An API object that manages external access to the services in a cluster, typically HTTP. Ingress may provide load balancing, SSL termination and name-based virtual hosting.

Introduction

When we have many services, there have many ports to manage. If we want to easy to manage. We can use the Ingress.

Follow this figure, we can see the how service and Ingress to work.

Use the ingress we only just use the hostname, then we can connect to the Pod. Because the ingress can automatically distribute. In Kubernetes there have no ingress-controller, so we need to install the ingress-controller.

(Installation guide https://hackmd.io/@CharlieChan/SkKXtrSgv)

Practice

We can use this yaml file to create the Ingress.

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: web
spec:
  rules:
    - host: blue.demo.com
      http:
        paths:
          - backend:
              serviceName: blue-service
              servicePort: 80
    - host: purple.demo.com
      http:
        paths:
          - backend:
              serviceName: purple-service
              servicePort: 80

Than we can use the kubectl get ingress to get the information. If we use the ingress, we need to edit the /etc/hosts let the DNS Server to find the hostname.

echo <node IP>   blue.demo.com  >> /etc/hosts
echo <node IP>   purple.demo.com >> /etc/hosts

Now we can type the blue.demo.com on browser, then we can see the picture like this.

Reference

https://medium.com/@C.W.Hu/kubernetes-implement-ingress-deployment-tutorial-7431c5f96c3e

https://kubernetes.io/docs/concepts/services-networking/ingress/