Target ports allows us to separate the port the service is available on from the port the application is listening on. TargetPort is the Port which the application is configured to listen on. Port is how the application will be accessed from the outside.

Similar to previously, the service and extra pods are deployed via kubectl apply -f clusterip-target.yaml

The following commands will create the service.

cat clusterip-target.yaml

kubectl get svc

kubectl describe svc/webapp1-clusterip-targetport-svc

After the service and pods have deployed, it can be accessed via the cluster IP as before, but this time on the defined port 8080.

export CLUSTER_IP=$(kubectl get services/webapp1-clusterip-targetport-svc -o go-template='{{(index .spec.clusterIP)}}') echo CLUSTER_IP=$CLUSTER_IP curl $CLUSTER_IP:8080

curl $CLUSTER_IP:8080

The application itself is still configured to listen on port 80. Kubernetes Service manages the translation between the two.

While TargetPort and ClusterIP make it available to inside the cluster, the NodePort exposes the service on each Node’s IP via the defined static port. No matter which Node within the cluster is accessed, the service will be reachable based on the port number defined.

kubectl apply -f nodeport.yaml

When viewing the service definition, notice the additional type and NodePort property defined cat nodeport.yaml

kubectl get svc

kubectl describe svc/webapp1-nodeport-svc

The service can now be reached via the Node's IP address on the NodePort defined.

curl [[HOST_IP]]:30080

Another approach to making a service available outside of the cluster is via External IP addresses.

Update the definition to the current cluster's IP address with sed -i 's/HOSTIP/[[HOST_IP]]/g' externalip.yaml

cat externalip.yaml

kubectl apply -f externalip.yaml

kubectl get svc

kubectl describe svc/webapp1-externalip-svc

The service is now bound to the IP address and Port 80 of the master node.

curl [[HOST_IP]]

When running in the cloud, such as EC2 or Azure, it's possible to configure and assign a Public IP address issued via the cloud provider. This will be issued via a Load Balancer such as ELB. This allows additional public IP addresses to be allocated to a Kubernetes cluster without interacting directly with the cloud provider.

As Katacoda is not a cloud provider, it's still possible to dynamically allocate IP addresses to LoadBalancer type services. This is done by deploying the Cloud Provider using kubectl apply -f cloudprovider.yaml. When running in a service provided by a Cloud Provider this is not required.

When a service requests a Load Balancer, the provider will allocate one from the 10.10.0.0/26 range defined in the configuration.

kubectl get pods -n kube-system

kubectl apply -f loadbalancer.yaml

The service is configured via a Load Balancer as defined in cat loadbalancer.yaml

While the IP address is being defined, the service will show Pending. When allocated, it will appear in the service list.

kubectl get svc

kubectl describe svc/webapp1-loadbalancer-svc

The service can now be accessed via the IP address assigned, in this case from the 10.10.0.0/26 range.

export LoadBalancerIP=$(kubectl get services/webapp1-loadbalancer-svc -o go-template='{{(index .status.loadBalancer.ingress 0).ip}}') echo LoadBalancerIP=$LoadBalancerIP curl $LoadBalancerIP

curl $LoadBalancerIP