CronHPA

Install the CronHPA controller

You can install the CronHPA controller ack-kubernetes-cronhpa-controller by using one of the following methods.

Method 1: Install the CronHPA controller on the Add-ons page in the ACK console

1. Log on to the ACK console.
2. In the left-side navigation pane of the ACK console, click Clusters.
3. You can go to the Add-ons page by using one of the following methods:
   • Method 1:
     1. On the Clusters page, find the cluster that you want to manage and click its name or click Details in the Actions column.
     2. In the left-side navigation pane of the details page, choose Operations > Add-ons.
   • Method 2

     On the Clusters page, find the cluster that you want to manage and choose More > Manage Components in the Actions column.

4. On the Add-ons page, click the Manage Applications tab, find ack-kubernetes-cronhpa-controller, and then click Install.

Method 2: Install the CronHPA controller from App Catalog

1. Log on to the ACK console.
2. In the left-side navigation pane of the ACK console, choose Marketplace > App Catalog.
3. On the Marketplace page, click the App Catalog tab and then find and click ack-kubernetes-cronhpa-controller.
4. On the ack-kubernetes-cronhpa-controller page, click Deploy.
5. In the Deploy wizard, select a cluster and a namespace, and then click Next.
6. On the Parameters wizard page, configure the required parameters and click OK.

You can uninstall the CronHPA controller if CronHPA is no longer used. For more information about how to uninstall ack-kubernetes-cronhpa-controller, see Manage system components or Delete a release.

Create CronHPA jobs

Before you create and run CronHPA jobs for your application, make sure that the CronHPA controller runs as normal in your cluster and only one HPA task is created for your application. For more information about how to enable CronHPA and HPA to interact without conflicts, see Enable CronHPA and HPA to interact without conflicts. You can create CronHPA jobs in the following scenarios.

Scenario 1: Create CronHPA jobs when you create an application

In the Scaling section on the Advanced wizard page, select Enable on the right side of CronHPA to create CronHPA jobs for the application. For more information about how to create an application, see Create a stateless application by using a Deployment or Use a StatefulSet to create a stateful application.

Scenario 2: Create CronHPA jobs for an existing application

The following example demonstrates how to create CronHPA jobs for an existing application. A stateless application is used in this example.

1. Log on to the ACK console.
2. In the left-side navigation pane of the ACK console, click Clusters.
3. 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.
4. In the left-side navigation pane of the details page, choose Workloads > Deployments.
5. On the Deployments page, find the application that you want to manage and click Details in the Actions column.
6. Click the Pod Scaling tab and configure CronHPA jobs.
   • If the CronHPA controller is not installed, the Install button appears on the page. Click Install and perform the following steps.
   • If the CronHPA controller is installed, perform the following steps.
7. Click Create to the right side of CronHPA. In the Create dialog box, configure CronHPA jobs.
   The following table describes the parameters.

   Parameter	Description
   Job Name	Enter a name for the CronHPA job. The name of each CronHPA job must be unique.
   Desired Number of Replicas	Replicated pods are scaled to the desired number at the scheduled time.
   Scaling Schedule	Set the scaling schedule. For more information about how to set the scaling schedule for a CronHPA job, see AliyunContainerService/kubernetes-cronhpa-controller.

Create or modify CronHPA jobs

1. Go to the Pod Scaling tab by performing the steps described in the preceding Create CronHPA jobs section.
2. On the Pod Scaling tab, find the created CronHPA job in the CronHPA section and click Add or Modify Job in the Actions column.
3. In the Edit dialog box, click Add Job to create CronHPA jobs. You can also modify existing CronHPA jobs. Click OK.
   To delete CronHPA jobs, perform the following steps:

   In the Edit dialog box, click the delete icon in the upper-right corner of the job that you want to delete. Click OK.

Enable CronHPA and HPA to interact without conflicts

CronHPA triggers horizontal scaling for containers based on schedules. HPA is used to scale pods to ensure the availability of your applications when network traffic spikes. If ACK detects that both CronHPA and HPA are deployed, ACK sets HPA as the scaling object of CronHPA. CronHPA triggers HPA to scale pods at the scheduled time.

The following YAML template shows the configurations of CronHPA and HPA:

apiVersion: autoscaling.alibabacloud.com/v1beta1
kind: CronHorizontalPodAutoscaler
metadata:
  labels:
    controller-tools.k8s.io: "1.0"
  name: cronhpa-sample
spec:
   scaleTargetRef:
      apiVersion: apps/v1
      kind: Deployment
      name: nginx-deployment-basic
   jobs:
   - name: "scale-down"
     schedule: "30 */1 * * * *"
     targetSize: 1
   - name: "scale-up"
     schedule: "0 */1 * * * *"
     targetSize: 11	
	

apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
  name: php-apache
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: nginx-deployment-basic
  minReplicas: 4
  maxReplicas: 10
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 50	
	

If both CronHPA and HPA are deployed, CronHPA and HPA may scale pods for the same application that is specified by scaleTargetRef. CronHPA and HPA are independent and unaware of each other. As a result, the CronHPA controller and the HPA controller scale pods for the application separately. The later scaling activity overwrites the earlier one.

Solution

The reason for the conflict between CronHPA and HPA is that the CronHPA controller and the HPA controller are unaware of each other. To resolve the conflict, CronHPA needs only to detect the status of HPA. In the HPA configuration, scaleTargetRef specifies the Deployment that is managed by HPA. The Deployment is related to a ReplicaSet. When HPA scales the Deployment, the ReplicaSet scales pods to the desired number. ACK modifies the CronHPA configuration by setting scaleTargetRef to HPA. CronHPA can find the application that is specified by scaleTargetRef in the HPA configuration. This enables CronHPA to detect the status of HPA.

apiVersion: autoscaling.alibabacloud.com/v1beta1
kind: CronHorizontalPodAutoscaler
metadata:
  labels:
    controller-tools.k8s.io: "1.0"
  name: cronhpa-sample
spec:
   scaleTargetRef:
      apiVersion: autoscaling/v1
      kind: HorizontalPodAutoscaler
      name:  nginx-deployment-basic-hpa
   jobs:
   - name: "scale-down"
     schedule: "30 */1 * * * *"
     targetSize: 1
     runOnce: true
   - name: "scale-up"
     schedule: "0 */1 * * * *"
     targetSize: 3
     runOnce: true

After you deploy the preceding YAML template, CronHPA is aware of the values of minReplicas, maxReplicas, and desiredReplicas in the HPA configuration. CronHPA is also aware of the current number of pods provisioned for the application that is specified by scaleTargetRef. CronHPA can detect the status of HPA by modifying the HPA configurations. CronHPA compares the desired number of pods with the current number of pods and then determines whether to trigger scaling activities and change the maximum number of pods in the HPA configuration. CronHPA also compares the desired number of pods with the maximum and minimum numbers of pods that are specified in the HPA configuration and then determines whether to change the minimum numbers of pods in the HPA configuration.

CronHPA does not directly change the number of pods for the Deployment. It triggers HPA to scale the pods. This resolves the conflict between CronHPA and HPA.