---
title: " Highly Available Kubernetes Clusters "
date: 2017-02-02
slug: highly-available-kubernetes-clusters
url: /blog/2017/02/Highly-Available-Kubernetes-Clusters
author: >
Jerzy Szczepkowski (Google)
---
Today’s post shows how to set-up a reliable, highly available distributed Kubernetes cluster. The support for running such clusters on Google Compute Engine (GCE) was added as an alpha feature in [Kubernetes 1.5 release](https://kubernetes.io/blog/2016/12/kubernetes-1-5-supporting-production-workloads/).
**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
```
Now, we will add two additional pools of worker nodes, each of three nodes, in zones europe-west1-c and europe-west1-d (more details on adding pools of worker nodes can be find [here](/docs/setup/multiple-zones/)):
```
$ KUBE\_USE\_EXISTING\_MASTER=true KUBE\_GCE\_ZONE=europe-west1-c ./cluster/kube-up.sh
$ KUBE\_USE\_EXISTING\_MASTER=true KUBE\_GCE\_ZONE=europe-west1-d ./cluster/kube-up.sh
```
To complete setup of HA cluster, we will add two master replicase, one in zone europe-west1-c, the other in europe-west1-d:
```
$ KUBE\_GCE\_ZONE=europe-west1-c KUBE\_REPLICATE\_EXISTING\_MASTER=true ./cluster/kube-up.sh
$ KUBE\_GCE\_ZONE=europe-west1-d KUBE\_REPLICATE\_EXISTING\_MASTER=true ./cluster/kube-up.sh
```
Note that adding the first replica will take longer (~15 minutes), as we need to reassign the IP of the master to the load balancer in front of replicas and wait for it to propagate (see [design doc](https://github.com/kubernetes/kubernetes/blob/master/docs/design/ha_master.md) for more details).
**Verifying in HA cluster works as intended**
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
```
Note that the second removal of replica will take longer (~15 minutes), as we need to reassign the IP of the load balancer in front of replicas to the remaining master and wait for it to propagate (see [design doc](https://github.com/kubernetes/kubernetes/blob/master/docs/design/ha_master.md) for more details).
Then, we will remove the additional worker nodes from zones europe-west1-c and europe-west1-d:
```
$ 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**
We have shown how, by adding worker node pools and master replicas, a Highly Available Kubernetes cluster can be created. As of Kubernetes version 1.5.2, it is supported in kube-up/kube-down scripts for GCE (as alpha). Additionally, there is a support for HA cluster on AWS in kops scripts (see [this article](http://kubecloud.io/setup-ha-k8s-kops/) for more details).
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