Horizontal pod autoscaling - Container Service for Kubernetes

You can create an application that has Horizontal Pod Autoscaling (HPA) enabled in the Container Service for Kubernetes (ACK) console. HPA can automatically scale container resources for your application. You can also use a YAML file to configure HPA settings.

Background information

In Kubernetes 1.18 and later versions, the v2beta2 API version allows you to use the behavior parameter of HPA to configure scaling settings. You can specify the scaleUp and scaleDown fields in the behavior parameter to specify scale-out and scale-in settings. If you want HPA to perform only scale-out operations or only scale-in operations, you can enable HPA in the ACK console and then click Disable Scale-in or Disable Scale-out.

By default, scale-out and scale-in are not disabled.
Disable scale-out: Set selectPolicy to Disabled in the scaleUp field to disable scale-out. Example:
```
behavior:
  scaleUp:
    selectPolicy: Disabled
```
Disable scale-in: Set selectPolicy to Disabled in the scaleDown field to disable scale-in. Example:
```
behavior:
  scaleDown:
    selectPolicy: Disabled
```

Create an application that has HPA enabled in the ACK console

ACK is integrated with HPA. You can create an application that has HPA enabled in the ACK console. You can enable HPA when you create an application or after the application is created.

Method 1: Enable HPA when you create an application

Log on to the ACK console.
In the left-side navigation pane of the ACK console, click Clusters.
On the Clusters page, find the cluster that you want to manage and click the name of the cluster or click Details in the Actions column. The details page of the cluster appears.
In the left-side navigation pane of the details page, choose Workloads > Deployments.
On the Deployments page, click Create from Image.

On the Basic Information wizard page, enter a name for your application, set the parameters, and then click Next.

Parameter	Description
Namespace	Select the namespace to which the application belongs. The default namespace is automatically selected.
Name	Enter a name for the application.
Replicas	The number of pods that you want to provision for the application. Default value: 2.
Type	The type of the application. You can select Deployment, StatefulSet, Job, CronJob, or DaemonSet.
Label	Add labels to the application. The labels are used to identify the application.
Annotations	Add annotations to the application.
Synchronize Timezone	This parameter is supported only by ACK clusters. ACK Serverless clusters do not support this parameter. This parameter specifies whether to synchronize the time zone between nodes and containers.

On the Container wizard page, set the container parameters, select an image, and then configure the required computing resources. Click Next. For more information, see Configure containers.
Note
You must configure the computing resources required by the Deployment. Otherwise, you cannot enable HPA.
On the Advanced wizard page, click Create to the right of Services in the Access Control section, and then set the parameters. For more information, see Configure advanced settings.

On the Advanced wizard page, select Enable for HPA and configure the scaling threshold and related settings.

Parameter	Description
Metric	Select CPU Usage or Memory Usage. The selected resource type must be the same as that specified in the Required Resources field.
Condition	Specify the resource usage threshold. HPA triggers scale-out events when the threshold is exceeded. For more information about the algorithms that are used to perform horizontal pod autoscaling, see Algorithm details.
Max. Replicas	Specify the maximum number of pods to which the Deployment can be scaled.
Min. Replicas	Specify the minimum number of pods that must run for the Deployment.
Disable Scale-in	If you want HPA to perform only scale-out operations or only scale-in operations, click Disable Scale-in or Disable Scale-out. For more information, see the Background information.
Disable Scale-out

In the lower-right corner of the Advanced wizard page, click Create to create the application that has HPA enabled.

Verify the result

Click View Details or choose Workloads > Deployments. On the page that appears, click the name of the created application or click Details in the Actions column. Then, click the Pod Scaling tab to view information about the scaling group of the application.
After the application starts running, container resources are automatically scaled based on the CPU utilization of the application. You can also check whether HPA is enabled in the staging environment by performing a CPU stress test on the pods of the application. Verify that the pods are automatically scaled within 30 seconds.

Method 2: Enable HPA for an existing application

The following example describes how to enable HPA for a Deployment.

Log on to the ACK console.
In the left-side navigation pane of the ACK console, click Clusters.
On the Clusters page, find the cluster that you want to manage and click the name of the cluster or click Details in the Actions column. The details page of the cluster appears.
In the left-side navigation pane of the details page, choose Workloads > Deployments.
On the Deployments page, click the name of the application that you want to manage.
Click the Pod Scaling tab and click Create.
In the Create dialog box, configure the HPA settings. For more information about how to set the parameters, see HPA settings in Step 9.
Click OK.

Create an application that has HPA enabled by using kubectl

You can also create an HPA by using an orchestration template and associate the HPA with the Deployment for which you want to enable HPA. Then, you can run kubectl commands to enable HPA.

In the following example, HPA is enabled for an NGINX application.

Create a file named nginx.yml and copy the following content to the file.

Example:

apiVersion: apps/v1 
kind: Deployment
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx  
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9 # replace it with your exactly <image_name:tags>
        ports:
        - containerPort: 80
        resources:
          requests:                         ## This parameter is required to run the HPA. 
            cpu: 500m

Run the following command to create an NGINX application:
```
kubectl create -f nginx.yml
```

Create an HPA.

Use the scaleTargetRef parameter to associate the HPA with the nginx Deployment.

YAML template for clusters whose Kubernetes versions are 1.24 and earlier

apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
  name: nginx-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: nginx
  minReplicas: 1
  maxReplicas: 10
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 50

YAML template for clusters whose Kubernetes versions are 1.26

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: nginx-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: nginx
  minReplicas: 1
  maxReplicas: 10
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 50

Note

You must configure resource requests for the pods of the application. Otherwise, the HPA cannot be started.

Run the kubectl describe hpa name command. The following output is an example of a warning that is returned:

Warning  FailedGetResourceMetric       2m (x6 over 4m)  horizontal-pod-autoscaler  missing request for cpu on container nginx in pod default/nginx-deployment-basic-75675f5897-mqzs7

Warning  FailedComputeMetricsReplicas  2m (x6 over 4m)  horizontal-pod-autoscaler  failed to get cpu utilization: missing request for cpu on container nginx in pod default/nginx-deployment-basic-75675f5

After the HPA is created, run the kubectl describe hpa name command.
If the following output is returned, the HPA is running as expected:
```
Normal SuccessfulRescale 39s horizontal-pod-autoscaler New size: 1; reason: All metrics below target
```
If the CPU utilization of the pod of the NGINX application exceeds 50% as specified in the HPA settings, the HPA automatically creates new pods. If the CPU utilization of the pod of the NGINX application drops below 50%, the HPA automatically removes pods.