Service

Each pod is assigned an IP address to make it reachable via the network, but the pods are considered ephemeral and may be deleted at any time.

To provide a stable way to address a set of pods (e.g. from a Deployment) we use a Service. There are a variety of kinds of services that provide access to pods from within or outside of the cluster.

Official docs: https://kubernetes.io/docs/concepts/services-networking/service/

Hands-On: Working with Services

We will create and examine multiple Services to understand their behavior.

1. Create a Namespace for the Examples

First, we'll create a namespace for these examples and set it as the default.

# task 01-create-namespace
# - Create a namespace for these examples and set as default
kubectl apply -f Namespace.yaml
kubens 04--service

2. Apply the Deployment Configuration

We need a set of pods to route traffic to. In this case we will use a deployment.

# task 02-apply-deployment
# - Apply the Deployment configuration
kubectl apply -f Deployment.yaml

3. ClusterIP Service

ClusterIP is the default type of Service.

It exposes the Service on a cluster-internal IP. Choosing this value makes the Service only reachable from within the cluster.

💡 Note: The selector for the Service defines a set of labels (in this case baz: pod-label) that are used to identify the set of pods to route traffic to. This same label must be applied ot the pod (in this case from the Deployment template spec).

# Service.nginx-clusterip.yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx-clusterip
  labels:
    foo: service-label
  annotations:
    bar: service-annotation
spec:
  type: ClusterIP
  selector:
    baz: pod-label
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

# task 03-apply-clusterip-service
# - Apply the ClusterIP Service.
kubectl apply -f Service.nginx-clusterip.yaml

4. NodePort Service

A NodePort type Service exposes the Service on each Node's IP at a static port (the NodePort).

A ClusterIP Service, to which the NodePort Service routes, is automatically created. You'll be able to contact the NodePort Service from outside the cluster, using <NodeIP>:<NodePort>.

🚨 Note: You will need to ensure your firewall rules allow inbound traffic on the corresponding port(s) for a NodePort to work!"

# Service.nginx-nodeport.yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx-nodeport
spec:
  type: NodePort
  selector:
    baz: pod-label
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80
      # nodePort: 30XXX (if unset, Kubernetes will assign a port within 30000-32767)

# task 04-apply-nodeport-service
# - Apply the NodePort Service
kubectl apply -f Service.nginx-nodeport.yaml

5. LoadBalancer Service

A LoadBalancer type Service exposes the Service externally using a cloud provider's load balancer.

NodePort and ClusterIP Services, to which the external load balancer routes, are automatically created.

# Service.nginx-loadbalancer.yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx-loadbalancer
spec:
  type: LoadBalancer
  selector:
    baz: pod-label
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

# task 05-apply-loadbalancer-service
# - Apply the LoadBalancer Service
kubectl apply -f Service.nginx-loadbalancer.yaml

6. Delete the Namespace to Clean Up

Finally, clean up by deleting the namespace, which will also delete all resources within it.

# task 06-delete-namespace
# - Delete the namespace to clean up
kubectl delete -f Namespace.yaml