Container Compute Service:Cron-based container scaling (CronHPA)

Install the CronHPA component

You can install the ack-kubernetes-cronhpa-controller component as follows.

1. Log on to the ACS console. In the left navigation pane, click Clusters.

2. On the Clusters page, click the name of the target cluster. In the left navigation pane, click Add-ons.

3. On the Add-ons page, click the Application Management tab. Find ack-kubernetes-cronhpa-controller, and click Install. In the dialog box that appears, click OK.

Create a CronHPA scheduled task

Before you create and run a CronHPA for an application, make sure the CronHPA component in the cluster is running correctly and the application has only one HPA object. For more information about the compatibility policy between CronHPA and HPA, see CronHPA compatibility with HPA. You can create a CronHPA task in one of the following two ways.

Method 1: Create a CronHPA task when you create an application

Method 2: Create a CronHPA task for an existing application

The following steps show how to create a CronHPA task for an existing stateless application.

1. Log on to the ACS console. In the left navigation pane, click Clusters.

2. On the Clusters page, click the name of the target cluster. In the left navigation pane, choose Workloads > Deployments.

3. On the Stateless page, click Details in the Actions column for the application.

4. Click the Container Scaling tab and configure the scheduled scaling task.

   • If the CronHPA component is not installed, a Click to install message appears. Click Click to install and then proceed with the following steps.

   • If the CronHPA component is already installed, proceed directly with the following steps.

5. Click Create next to Cron-based Scaling (CronHPA). In the Create dialog box, set the parameters for the scheduled scaling task.

   

   The following table describes the configuration items.

   Configuration Item	Description
   Task Name	Define a name for the scheduled task. The name of each task must be unique.
   Target Replicas	The number of application replicas automatically scales to this value at the scheduled time.
   Scheduling Cycle	Set the scheduling cycle. For more information about how to set the scheduling cycle for a scheduled scaling task, see predefined-schedules.

Add or modify a scheduled scaling task

1. Follow the steps in Create a CronHPA scheduled task to go to the Container Scaling page.

2. On the Container Scaling tab, in the Cron-based Scaling (CronHPA) section, find the target task and click Add or Edit Task in the Actions column.

3. In the Edit dialog box, click Add Task to create a task, or click an existing CronHPA task to modify it. Then, click OK.

   

   Note

   You can delete a CronHPA task as shown in the following figure. In the Edit dialog box, click the delete icon in the upper-right corner of the task name, and then click OK.

CronHPA and HPA definition templates

CronHPA compatibility with HPA

Both CronHPA and HPA act on workloads, such as deployments or StatefulSets. Configuring both on the same workload can cause conflicts. To solve this problem, CronHPA supports targeting an HPA as its scaling object, which makes it compatible with the original functionality of HPA.

If you set both CronHPA and HPA, they might try to operate on the same scaleTargetRef at the same time. Because CronHPA and HPA are independent and unaware of each other, the two controllers would work separately, and the later operation would overwrite the earlier one.

Solution for CronHPA and HPA compatibility

The conflict can be resolved if CronHPA is aware of the current state of HPA. To achieve this, ACS sets the scaleTargetRef in CronHPA to the HPA object itself, not the final workload object. When CronHPA performs a scaling operation, it first finds the real scaleTargetRef through the HPA object. It then adjusts the workload object based on this state. This prevents overwrites and ensures that scaling operations are consistent and predictable.

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: false
   - name: "scale-up"
     schedule: "0 */1 * * * *"
     targetSize: 3
     runOnce: false

With the CronHPA definition above, CronHPA can read the values of spec.minReplicas, spec.maxReplicas, and status.desiredReplicas from the HPA. It also knows the current number of replicas for the spec.scaleTargetRef in the HPA. CronHPA interacts with the HPA by adjusting it. CronHPA compares its target number of replicas with the current number of replicas and takes the larger value to decide whether to scale out or modify the HPA's upper limit. CronHPA compares its target number of replicas with the HPA's configuration and takes the smaller value to decide whether to modify the HPA's lower limit.

As shown above, CronHPA does not directly adjust the number of replicas in a deployment. Instead, it operates on the deployment through the HPA. This avoids conflicts between HPA and CronHPA.