Kubernetes - Service


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A service can be defined as a logical set of pods. It can be defined as an abstraction on the top of the pod which provides a single IP address and DNS name by which pods can be accessed. With Service, it is very easy to manage load balancing configuration. It helps pods to scale very easily.

A service is a REST object in Kubernetes whose definition can be posted to Kubernetes apiServer on the Kubernetes master to create a new instance.

Service without Selector

apiVersion: v1
kind: Service
metadata:
   name: Tutorial_point_service
spec:
   ports:
   - port: 8080
   targetPort: 31999

The above configuration will create a service with the name Tutorial_point_service.

Service Config File with Selector

apiVersion: v1
kind: Service
metadata:
   name: Tutorial_point_service
spec:
   selector:
      application: "My Application" -------------------> (Selector)
   ports:
   - port: 8080
   targetPort: 31999

In this example, we have a selector; so in order to transfer traffic, we need to create an endpoint manually.

apiVersion: v1
kind: Endpoints
metadata:
   name: Tutorial_point_service
subnets:
   address:
      "ip": "192.168.168.40" -------------------> (Selector)
   ports:
      - port: 8080

In the above code, we have created an endpoint which will route the traffic to the endpoint defined as “192.168.168.40:8080”.

Multi-Port Service Creation

apiVersion: v1
kind: Service
metadata:
   name: Tutorial_point_service
spec:
   selector:
      application: “My Application” -------------------> (Selector)
   ClusterIP: 10.3.0.12
   ports:
      -name: http
      protocol: TCP
      port: 80
      targetPort: 31999
   -name:https
      Protocol: TCP
      Port: 443
      targetPort: 31998

Types of Services

ClusterIP − This helps in restricting the service within the cluster. It exposes the service within the defined Kubernetes cluster.

spec:
   type: NodePort
   ports:
   - port: 8080
      nodePort: 31999
      name: NodeportService

NodePort − It will expose the service on a static port on the deployed node. A ClusterIP service, to which NodePort service will route, is automatically created. The service can be accessed from outside the cluster using the NodeIP:nodePort.

spec:
   ports:
   - port: 8080
      nodePort: 31999
      name: NodeportService
      clusterIP: 10.20.30.40

Load Balancer − It uses cloud providers’ load balancer. NodePort and ClusterIP services are created automatically to which the external load balancer will route.

A full service yaml file with service type as Node Port. Try to create one yourself.

apiVersion: v1
kind: Service
metadata:
   name: appname
   labels:
      k8s-app: appname
spec:
   type: NodePort
   ports:
   - port: 8080
      nodePort: 31999
      name: omninginx
   selector:
      k8s-app: appname
      component: nginx
      env: env_name


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