Verifying and Testing HA Cluster Functionality

kubernetes-minion-group-6s52 Ready 39m kubernetes-minion-group-cw8e Ready 48m kubernetes-minion-group-fw91 Ready 48m kubernetes-minion-group-h2kn Ready 31m kubernetes-minion-group-ietm Ready 39m kubernetes-minion-group-j6lf Ready 31m kubernetes-minion-group-soj7 Ready 31m kubernetes-minion-group-tj82 Ready 39m kubernetes-minion-group-vd96 Ready 48m ``` As we can see, we have 3 master replicas (with disabled scheduling) and 9 worker nodes. We will deploy a sample application (nginx server) to verify that our cluster is working correctly: ``` $ kubectl run nginx --image=nginx --expose --port=80 ``` After waiting for a while, we can verify that both the deployment and the service were correctly created and are running: ``` $ kubectl get pods NAME READY STATUS RESTARTS AGE ... nginx-3449338310-m7fjm 1/1 Running 0 4s ... $ kubectl run -i --tty test-a --image=busybox /bin/sh If you don't see a command prompt, try pressing enter. # wget -q -O- http://nginx.default.svc.cluster.local ... \<title\>Welcome to nginx!\</title\> ... ``` Now, let’s simulate failure of one of master’s replicas by executing halt command on it (kubernetes-master-137, zone europe-west1-c): ``` $ gcloud compute ssh kubernetes-master-2d4 --zone=europe-west1-c ... $ sudo halt ``` After a while the master replica will be marked as NotReady: ``` $ kubectl get nodes NAME STATUS AGE kubernetes-master Ready,SchedulingDisabled 51m kubernetes-master-2d4 NotReady,SchedulingDisabled 8m kubernetes-master-85f Ready,SchedulingDisabled 4m ... ``` However, the cluster is still operational. We may verify it by checking if our nginx server works correctly: ``` $ kubectl run -i --tty test-b --image=busybox /bin/sh If you don't see a command prompt, try pressing enter. # wget -q -O- http://nginx.default.svc.cluster.local ... \<title\>Welcome to nginx!\</title\> ... ``` We may also run another nginx server: ``` $ kubectl run nginx-next --image=nginx --expose --port=80 ``` The new server should be also working correctly: ``` $ kubectl run -i --tty test-c --image=busybox /bin/sh If you don't see a command prompt, try pressing enter. # wget -q -O- http://nginx-next.default.svc.cluster.local

The provided text details the process of verifying and testing the functionality of a High Availability (HA) Kubernetes cluster. It includes steps to deploy an Nginx server to confirm the cluster's operational status, simulating a master replica failure by halting one of the master nodes, and verifying that the cluster remains operational by confirming the Nginx server still works and deploying a new one. This demonstrates the HA cluster's resilience to node failures.