Kubernetes - Services

Introduction

• Kubernetes Services are an abstract way to expose an application running on a set of Pods as a network service.
• They provide a stable and reliable way to communicate with or access the pods in a Kubernetes cluster.
• Services enable loose coupling between dependent Pods.
• Types of Services:

1. ClusterIP

• This creates a virtual IP inside the cluster to enable communication between different services.

• Internal to k8s cluster

  

• Sample YAML:

    apiVersion: v1
    kind: Service
    metadata:  
      name: my-internal-service
    spec:
      selector:    
        app: my-app
      type: ClusterIP
      ports:  
      - name: http
        port: 80
        targetPort: 80
        protocol: TCP
  

2. NodePort

• NodePort opens a specific port on all the Nodes and any traffic that is sent to the port is forwarded to the service.

• Access to Internet/Outside cluster.

  

• Sample YAML:

    apiVersion: v1
    kind: Service
    metadata:  
      name: my-nodeport-service
    spec:
      selector:    
        app: my-app
      type: NodePort
      ports:  
      - name: http
        port: 80
        targetPort: 80
        nodePort: 30036
        protocol: TCP
  

3. LoadBalancer

• This service provisions a load balancer for your application in supported cloud providers (like Amazon Web Services(AWS), Google Cloud Platform(GCP), Azure, etc.)

• It exposes the service externally using the load balancer. The external load balancer routes the traffic to backend Pods.

  

• Sample YAML:

    apiVersion: v1
    kind: Service
    metadata:
    name: my-loadbalancer-service
    spec:
    selector:
        app: my-app
    type: LoadBalancer
    ports:
        - protocol: TCP
        port: 80
        targetPort: 9376
  

4. externalName

• To access externally hosted apps in k8s cluster
• From external/internal

• Example: Access AWS RDS database endpoint by application inside k8 cluster)

  

• Sample YAML:

    apiVersion: v1
    kind: Service
    metadata:
    name: my-externalname-service
    spec:
    type: ExternalName
    externalName: my.database.example.com