Motivation

We will create a Highly Available Kubernetes cluster, with master replicas and worker nodes distributed among three zones of a region. Such setup will ensure that the cluster will continue operating during a zone failure.

Setting Up HA cluster

The following instructions apply to GCE. First, we will setup a cluster that will span over one zone (europe-west1-b), will contain one master and three worker nodes and will be HA-compatible (will allow adding more master replicas and more worker nodes in multiple zones in future). To implement this, we’ll export the following environment variables:

$ export KUBERNETES\_PROVIDER=gce

$ export NUM\_NODES=3

$ export MULTIZONE=true

$ export ENABLE\_ETCD\_QUORUM\_READ=true

and run kube-up script (note that the entire cluster will be initially placed in zone europe-west1-b):

$ KUBE\_GCE\_ZONE=europe-west1-b ./cluster/kube-up.sh

We may now list all nodes present in the cluster:

$ kubectl get nodes

NAME                      STATUS                AGE

kubernetes-master         Ready,SchedulingDisabled 48m

kubernetes-master-2d4     Ready,SchedulingDisabled 5m

kubernetes-master-85f     Ready,SchedulingDisabled 32s

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

...

\<title\>Welcome to nginx!\</title\>

...

Let’s now reset the broken replica:

$ gcloud compute instances start kubernetes-master-2d4 --zone=europe-west1-c

After a while, the replica should be re-attached to the cluster:

$ kubectl get nodes

NAME                      STATUS                AGE

kubernetes-master         Ready,SchedulingDisabled 57m

kubernetes-master-2d4     Ready,SchedulingDisabled 13m

kubernetes-master-85f     Ready,SchedulingDisabled 9m

...

Shutting down HA cluster

To shutdown the cluster, we will first shut down master replicas in zones D and E:

$ KUBE\_DELETE\_NODES=false KUBE\_GCE\_ZONE=europe-west1-c ./cluster/kube-down.sh


$ KUBE\_DELETE\_NODES=false KUBE\_GCE\_ZONE=europe-west1-d ./cluster/kube-down.sh

$ KUBE\_USE\_EXISTING\_MASTER=true KUBE\_GCE\_ZONE=europe-west1-c ./cluster/kube-down.sh


$ KUBE\_USE\_EXISTING\_MASTER=true KUBE\_GCE\_ZONE=europe-west1-d ./cluster/kube-down.sh

And finally, we will shutdown the remaining master with the last group of nodes (zone europe-west1-b):

$ KUBE\_GCE\_ZONE=europe-west1-b ./cluster/kube-down.sh

Conclusions

--Jerzy Szczepkowski, Software Engineer, Google