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Services in Kubernetes

Kubernetes Services are an abstraction that defines a logical set of pods and a policy by which to access them. This is useful for exposing applications running in pods to other applications or external traffic.

Types of Services

Kubernetes supports several types of services, each serving a different purpose:

  • ClusterIP: The default type, which exposes the service on a cluster-internal IP. This means the service is only accessible within the cluster.
  • NodePort: Exposes the service on each node’s IP at a static port. This allows external traffic to access the service by requesting <NodeIP>:<NodePort>.
  • LoadBalancer: Creates an external load balancer in supported cloud providers, which routes traffic to the service.
  • ExternalName: Maps the service to the contents of the externalName field (e.g., a DNS name), allowing you to access external services.

Example of a NodePort Service

apiVersion: v1
kind: Service
metadata:
  name: my-nodeport-service
spec:
  type: NodePort
  selector:
    app: my-app  # Select pods with this label
  ports:
  - port: 80
    targetPort: 8080
    nodePort: 30007

# Create the NodePort service
kubectl apply -f my-nodeport-service.yaml
# Get the details of the service
kubectl get services
# Access the service from outside the cluster
curl http://<NodeIP>:30007

Example of a ClusterIP Service

apiVersion: v1
kind: Service
metadata:
  name: my-clusterip-service
spec:
  type: ClusterIP
  selector:
    app: my-app
  ports:
  - port: 80
    targetPort: 8080

# Create the ClusterIP service
kubectl apply -f my-clusterip-service.yaml
# Get the details of the service
kubectl get services
# Access the service from within the cluster
kubectl exec -it <pod-name> -- curl http://my-clusterip-service:80