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If you've followed the tutorials, you have a working Kubernetes cluster in AKS and you deployed the sample Azure Voting app. In this tutorial, part five of seven, you scale out the pods in the app and try pod autoscaling. You also learn how to scale the number of Azure VM nodes to change the cluster's capacity for hosting workloads. You learn how to:

In later tutorials, the Azure Vote application is updated to a new version.

Before you begin

In previous tutorials, an application was packaged into a container image. This image was uploaded to Azure Container Registry, and you created an AKS cluster. The application was then deployed to the AKS cluster. If you haven't done these steps, and would like to follow along, start with Tutorial 1 – Create container images .

This tutorial requires that you're running Azure PowerShell version 5.9.0 or later. Run Get-InstalledModule -Name Az to find the version. If you need to install or upgrade, see Install Azure PowerShell .

Manually scale pods

When the Azure Vote front-end and Redis instance were deployed in previous tutorials, a single replica was created. To see the number and state of pods in your cluster, use the kubectl get command as follows:

kubectl get pods
The following example output shows one front-end pod and one back-end pod:
NAME                               READY     STATUS    RESTARTS   AGE
azure-vote-back-2549686872-4d2r5   1/1       Running   0          31m
azure-vote-front-848767080-tf34m   1/1       Running   0          31m
To manually change the number of pods in the azure-vote-front deployment, use the kubectl scale command. The following example increases the number of front-end pods to 5:
kubectl scale --replicas=5 deployment/azure-vote-front
Run kubectl get pods again to verify that AKS successfully creates the additional pods. After a minute or so, the pods are available in your cluster:
kubectl get pods
                                    READY     STATUS    RESTARTS   AGE
azure-vote-back-2606967446-nmpcf    1/1       Running   0          15m
azure-vote-front-3309479140-2hfh0   1/1       Running   0          3m
azure-vote-front-3309479140-bzt05   1/1       Running   0          3m
azure-vote-front-3309479140-fvcvm   1/1       Running   0          3m
azure-vote-front-3309479140-hrbf2   1/1       Running   0          15m
azure-vote-front-3309479140-qphz8   1/1       Running   0          3m
Autoscale pods
Azure CLI
Azure PowerShell
Kubernetes supports horizontal pod autoscaling to adjust the number of pods in a deployment depending on CPU utilization or other select metrics. The Metrics Server is used to provide resource utilization to Kubernetes, and is automatically deployed in AKS clusters versions 1.10 and higher. To see the version of your AKS cluster, use the az aks show command, as shown in the following example:
az aks show --resource-group myResourceGroup --name myAKSCluster --query kubernetesVersion --output table
Kubernetes supports horizontal pod autoscaling to adjust the number of pods in a deployment depending on CPU utilization or other select metrics. The Metrics Server is used to provide resource utilization to Kubernetes, and is automatically deployed in AKS clusters versions 1.10 and higher. To see the version of your AKS cluster, use the Get-AzAksCluster cmdlet, as shown in the following example:
(Get-AzAksCluster -ResourceGroupName myResourceGroup -Name myAKSCluster).KubernetesVersion
If your AKS cluster is less than 1.10, the Metrics Server is not automatically installed. Metrics Server installation manifests are available as a components.yaml asset on Metrics Server releases, which means you can install them via a url. To learn more about these YAML definitions, see the Deployment section of the readme.
Example installation:
kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/download/v0.3.6/components.yaml
To use the autoscaler, all containers in your pods and your pods must have CPU requests and limits defined. In the azure-vote-front deployment, the front-end container already requests 0.25 CPU, with a limit of 0.5 CPU.
These resource requests and limits are defined for each container as shown in the following example snippet:
  containers:
  - name: azure-vote-front
    image: mcr.microsoft.com/azuredocs/azure-vote-front:v1
    ports:
    - containerPort: 80
    resources:
      requests:
        cpu: 250m
      limits:
        cpu: 500m
The following example uses the kubectl autoscale command to autoscale the number of pods in the azure-vote-front deployment. If average CPU utilization across all pods exceeds 50% of their requested usage, the autoscaler increases the pods up to a maximum of 10 instances. A minimum of 3 instances is then defined for the deployment:
kubectl autoscale deployment azure-vote-front --cpu-percent=50 --min=3 --max=10
Alternatively, you can create a manifest file to define the autoscaler behavior and resource limits. The following is an example of a manifest file named azure-vote-hpa.yaml.
apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:
  name: azure-vote-back-hpa
spec:
  maxReplicas: 10 # define max replica count
  minReplicas: 3  # define min replica count
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: azure-vote-back
  targetCPUUtilizationPercentage: 50 # target CPU utilization
apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:
  name: azure-vote-front-hpa
spec:
  maxReplicas: 10 # define max replica count
  minReplicas: 3  # define min replica count
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: azure-vote-front
  targetCPUUtilizationPercentage: 50 # target CPU utilization
Use kubectl apply to apply the autoscaler defined in the azure-vote-hpa.yaml manifest file.
kubectl apply -f azure-vote-hpa.yaml
To see the status of the autoscaler, use the kubectl get hpa command as follows:
kubectl get hpa
NAME               REFERENCE                     TARGETS    MINPODS   MAXPODS   REPLICAS   AGE
azure-vote-front   Deployment/azure-vote-front   0% / 50%   3         10        3          2m
After a few minutes, with minimal load on the Azure Vote app, the number of pod replicas decreases automatically to three. You can use kubectl get pods again to see the unneeded pods being removed.
For additional examples on using the horizontal pod autoscaler, see HorizontalPodAutoscaler Walkthrough.
Manually scale AKS nodes
If you created your Kubernetes cluster using the commands in the previous tutorial, it has two nodes. You can adjust the number of nodes manually if you plan more or fewer container workloads on your cluster.
The following example increases the number of nodes to three in the Kubernetes cluster named myAKSCluster. The command takes a couple of minutes to complete.
Azure CLI
Azure PowerShell
az aks scale --resource-group myResourceGroup --name myAKSCluster --node-count 3
When the cluster has successfully scaled, the output is similar to following example:
"agentPoolProfiles": [
    "count": 3,
    "dnsPrefix": null,
    "fqdn": null,
    "name": "myAKSCluster",
    "osDiskSizeGb": null,
    "osType": "Linux",
    "ports": null,
    "storageProfile": "ManagedDisks",
    "vmSize": "Standard_D2_v2",
    "vnetSubnetId": null
Get-AzAksCluster -ResourceGroupName myResourceGroup -Name myAKSCluster | Set-AzAksCluster -NodeCount 3
When the cluster has successfully scaled, the output is similar to following example:
ProvisioningState       : Succeeded
MaxAgentPools           : 100
KubernetesVersion       : 1.19.9
DnsPrefix               : myAKSCluster
Fqdn                    : myakscluster-000a0aa0.hcp.eastus.azmk8s.io
PrivateFQDN             :
AgentPoolProfiles       : {default}
WindowsProfile          : Microsoft.Azure.Commands.Aks.Models.PSManagedClusterWindowsProfile
AddonProfiles           : {}
NodeResourceGroup       : MC_myresourcegroup_myAKSCluster_eastus
EnableRBAC              : True
EnablePodSecurityPolicy :
NetworkProfile          : Microsoft.Azure.Commands.Aks.Models.PSContainerServiceNetworkProfile
AadProfile              :
ApiServerAccessProfile  :
Identity                :
LinuxProfile            : Microsoft.Azure.Commands.Aks.Models.PSContainerServiceLinuxProfile
ServicePrincipalProfile : Microsoft.Azure.Commands.Aks.Models.PSContainerServiceServicePrincipalProfile
Id                      : /subscriptions/00000000-0000-0000-0000-000000000000/resourcegroups/myresourcegroup/providers/Micros
                          oft.ContainerService/managedClusters/myAKSCluster
Name                    : myAKSCluster
Type                    : Microsoft.ContainerService/ManagedClusters
Location                : eastus
Tags                    : {}
Next steps
In this tutorial, you used different scaling features in your Kubernetes cluster. You learned how to:
Manually scale Kubernetes pods that run your application
Configure autoscaling pods that run the app front-end
Manually scale the Kubernetes nodes
Advance to the next tutorial to learn how to update application in Kubernetes.
Update an application in Kubernetes