Azure Kubernetes cluster across Availability Zones

Availability Zone is high-availability offering that protects applications and data from datacenter failures. Availability Zones are unique physical locations within an Azure region, each zone is equipped with independent power, cooling, and networking, there’s a minimum of three separate zones in all enabled regions.

AKS cluster nodes can be deployed across multiple zones with in Azure region for high availability and business continuity.

Limitations

• Availability zones can  be defined only when creating the cluster or node pool.
• Availability zone settings can’t be updated after the cluster is created.
• Node size(SKU) selected must be available across all availability zones selected.
• Azure Standard Load Balancers is required for clusters with availability zones enabled.

Create an AKS cluster across availability zones

When creating cluster using “az aks create” command,  --zones parameter defines which zones agent nodes are deployed into, etcd or the cluster APIs are spread across the available zones in the region during the creation. run the above command in azure cli to create 3 nodes in 3 different zones in eastus2 region, as my resource group( aks-az-rg) is in eastus2.

az aks create --resource-group aks-az-rg --name AKS-AZ-Cluster --generate-ssh-keys --vm-set-type VirtualMachineScaleSets --load-balancer-sku standard --node-count 3 --zones 1 2 3

Verify Node Distribution

Run “get-credentials” to setup kubeconfig and then verify the node details using kubectl describe command in bash, you can also verify on azure portal.

az aks get-credentials --resource-group aks-az-rg --name AKS-AZ-Cluster

kubectl describe nodes | grep -e "Name:" -e "failure-domain.beta.kubernetes.io/zone"

Three nodes are distributed across three zones, eastus2-1, eastus2-2 and eastus2-3,if you scale node pool Azure platform automatically distributes new nodes across zones.

az aks scale --resource-group aks-az-rg --name AKS-AZ-Cluster --node-count 5

Verify POd distrubtion

Let’s deploy image with three replicas and verify how pods are distributed, run the below command in azure cli to deploy NGINX with three replicas.

kubectl create deployment nginx --image=mcr.microsoft.com/oss/nginx/nginx:1.15.5-alpine

kubectl scale deployment nginx --replicas=3

By viewing nodes where pods are running, you see pods are running on the nodes corresponding to three different availability zones. run the below command in a Bash to verify node where the pod is running.

kubectl describe pod | grep -e "^Name:" -e "^Node:"

The first pod is running on node 3, which is located in the availability zone eastus2-1. The second pod is running on node 1 which corresponds to eastus2-2, and the third one in node 2, in eastus2-3. Without any additional configuration, Kubernetes is spreading the pods correctly across all three availability zones.

Conclusion

if you are running application with higher SLA on AKS , take advantage of high availability with Azure Availability Zones as a part of your comprehensive business continuity and disaster recovery strategy with built-in security, and flexible, high-performance architecture.

Helpful Links: https://docs.microsoft.com/en-us/azure/aks/availability-zones

Azure Kubernetes cluster across Availability Zones

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