Use CronHPA to scale Pods based on a schedule - Container Service for Kubernetes

How it works

CronHPA is built on kubernetes-cronhpa-controller, a time-based horizontal scaling controller. At each scheduled trigger time, CronHPA sets the target workload's replica count to targetSize. After that, CronHPA takes no further action until the next scheduled trigger fires.

CronHPA is a trigger-point model, not a time-window model. It sets the replica count once at the trigger time and does not maintain that count. If another controller (such as HPA) adjusts replicas in between, CronHPA does not intervene until its next trigger fires.

CronHPA works with any Kubernetes object that supports scale subresources, such as Deployment and StatefulSet.

Prerequisites

Before you begin, ensure that you have:

An ACK managed cluster or ACK Serverless cluster. For more information, see Create an ACK Managed Cluster and Create an ACK Serverless Cluster.
A kubectl client connected to the cluster. For more information, see Connect to Kubernetes cluster using kubectl.

Step 1: Install the CronHPA component

Install the ack-kubernetes-cronhpa-controller add-on to enable CronHPA in your cluster.

Log on to the ACK console. In the left-side navigation pane, click Clusters.
On the Clusters page, click the name of the target cluster. In the left-side navigation pane, choose Operations > Add-ons.
On the Manage Applications tab, find ack-kubernetes-cronhpa-controller, click Install, and follow the prompts to complete the installation.

Step 2: Create a CronHPA job

Before creating a CronHPA job, confirm that:

The ack-kubernetes-cronhpa-controller component is running normally in the cluster.
The target workload has at most one Horizontal Pod Autoscaler (HPA) configured.

The following sections use a Deployment as an example. The steps are similar for other workload types.

Option 1: Create a CronHPA job when creating a new application

Log on to the ACK console. In the left-side navigation pane, click Clusters.
On the Clusters page, click the name of the target cluster. In the left-side navigation pane, choose Workloads > Deployments.
On the Deployments page, click Create from Image.

Complete the Basic Information, Container, and other configuration sections. When you reach Advanced, expand the Scaling section, enable CronHPA, and configure the following parameters: For all other configuration steps and parameters, see Create a stateless application by using a Deployment.

Parameter	Description
Job Name	The name of the CronHPA job.
Desired Number of Replicas	The target replica count when the scheduled time is reached.
Scaling Schedule	The cron expression defining the trigger schedule. See Cron expression format.

Option 2: Create a CronHPA job for an existing application

Workloads page

From the Deployments page:

Log on to the ACK console. In the left-side navigation pane, click Clusters.
On the Clusters page, click the name of the target cluster. In the left-side navigation pane, choose Workloads > Deployments.
On the Deployments page, click Details in the Actions column of the target Deployment, then click the Pod Scaling tab.

In the CronHPA section, click Create and configure the following parameters:

Parameter	Description
Job Name	The name of the CronHPA job.
Desired Number of Replicas	The target replica count when the scheduled time is reached.
Scaling Schedule	The cron expression defining the trigger schedule. See Cron expression format.

create

Workload scaling page

From the Workload Scaling page (allowlist required):

The Workload Scaling page is available only to accounts on the allowlist. To request access, submit a ticket.

Log on to the ACK console. In the left-side navigation pane, click Clusters.
On the Clusters page, click the name of the target cluster. In the left-side navigation pane, choose Auto Scaling > Workload Scaling.
In the upper-right corner, click Create Auto Scaling, select the target workload, and click the Horizontal Scaling tab.

Select the CronHPA option and configure the following parameters:

Parameter	Description
CronHPA Name	The name of the CronHPA resource.
Job Name	The name of the CronHPA job.
Desired Number of Replicas	The target replica count when the scheduled time is reached.
Scaling Schedule	The cron expression defining the trigger schedule. See Cron expression format.

CronHPA YAML reference

CronHPA is configured as a CronHorizontalPodAutoscaler custom resource. The following example scales a Deployment down to 1 replica at 30 seconds past each hour, and up to 3 replicas at the top of each hour, skipping November 15th and every Friday.

apiVersion: autoscaling.alibabacloud.com/v1beta1
kind: CronHorizontalPodAutoscaler
metadata:
  labels:
    controller-tools.k8s.io: "1.0"
  name: cronhpa-sample
  namespace: default
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: nginx-deployment-basic
  excludeDates:
    # Skip November 15th
    - "* * * 15 11 *"
    # Skip every Friday
    - "* * * * * 5"
  jobs:
    - name: "scale-down"
      schedule: "30 */1 * * * *"
      targetSize: 1
    - name: "scale-up"
      schedule: "0 */1 * * * *"
      targetSize: 3
      runOnce: false

Parameters

Parameter	Description
`scaleTargetRef`	The workload to scale. The target object must support scale subresources.
`excludeDates`	A list of dates on which all jobs are skipped. Granularity is one day. Use the 6-field cron format: `"<Seconds> <Minutes> <Hours> <Day of month> <Month> <Day of week>"`.
`jobs[].name`	The job name. Must be unique within the CronHPA resource.
`jobs[].schedule`	The cron expression that defines when the job fires. Uses the Go `go-cron` library. See Cron expression format.
`jobs[].targetSize`	The number of replicas to scale to when the job fires.
`jobs[].runOnce`	When set to `true`, the task executes only once and exits after the first execution. Default: `false`.

Cron expression format

CronHPA uses a 6-field cron expression (seconds-first), unlike standard 5-field crontab syntax.

<Seconds> <Minutes> <Hours> <Day of month> <Month> <Day of week>

Field	Required	Allowed values	Special characters
Seconds	Yes	0–59	`* / , -`
Minutes	Yes	0–59	`* / , -`
Hours	Yes	0–23	`* / , -`
Day of month	Yes	1–31	`* / , - ?`
Month	Yes	1–12 or JAN–DEC	`* / , -`
Day of week	Yes	0–6 or SUN–SAT	`* / , - ?`

Common schedule examples:

Schedule	Meaning
`0 0 8 * * *`	Every day at 08:00
`0 0 18 * * 1-5`	Weekdays (Mon–Fri) at 18:00
`0 0 /1 * *`	Every hour, on the hour
`0 30 /1 * *`	Every hour, at 30 minutes past
`0 0 8 * * 1-5`	Weekdays at 08:00 (scale up for business hours)
`0 0 20 * * 1-5`	Weekdays at 20:00 (scale down after business hours)

For the full expression reference, see the kubernetes-cronhpa-controller documentation.

More operations

View, add, or edit CronHPA jobs

After creating CronHPA jobs, you can view their status and edit the configuration from the following entry points:

Workload Scaling page: In the left-side navigation pane, choose Auto Scaling > Workload Scaling. On the Horizontal Scaling tab, find the target CronHPA in the CronHPA section and click Edit in the Actions column.
Deployments page: In the left-side navigation pane, choose Workloads > Deployments. Click Details for the target Deployment, then click the Pod Scaling tab. In the CronHPA section, click Add or Edit Job in the Actions column.

Coordinate CronHPA with HPA

CronHPA and HPA operate independently and are unaware of each other. If both are configured for the same workload, their scaling actions may conflict — the later action overwrites the earlier one.

To resolve this conflict, if ACK detects that both CronHPA and HPA are deployed, it sets the scaling target of CronHPA to HPA, thereby enabling scheduled scaling for the HPA scaling object, such as a Deployment.

For setup instructions, see Implement coordination between CronHPA and HPA.

FAQ

How do I uninstall ack-kubernetes-cronhpa-controller?

Log on to the ACK console. In the left-side navigation pane, click Clusters.
On the Clusters page, click the name of the target cluster. In the left-side navigation pane, choose Applications > Helm.
On the Helm page, check whether the ack-kubernetes-cronhpa-controller component exists.
- If it exists, click Delete in the Actions column. > Important: Deleting the component via Helm does not delete the Custom Resource Definition (CRD) or any CronHPA task resources. Delete those manually after uninstalling the component.
- If it does not exist, proceed to the next step.
In the left-side navigation pane, choose Operations > Add-ons.
On the Add-ons page, find ack-kubernetes-cronhpa-controller and click Uninstall.

What's next

Scale pods based on CPU utilization, memory, or custom metrics: Implement Horizontal Pod Autoscaler (HPA)
Automatically identify resource usage cycles and scale based on historical metrics: Predictive scaling based on Advanced Horizontal Pod Autoscaling (AHPA)
Automatically right-size pod resource limits based on actual usage: Vertical Pod Autoscaler (VPA)
Scale pods based on message queues, timing strategies, custom metrics, and other Kubernetes events: ACK KEDA (Kubernetes Event-driven Autoscaling)

Container Service for Kubernetes:Use CronHPA for scheduled Pod scaling