Container Service for Kubernetes:Use Knative and AHPA to implement scheduled auto scaling

Step 1: Use AHPA to configure metrics for auto scaling

Use the following YAML template to create an AHPA configuration file and deploy it to the cluster:

apiVersion: autoscaling.alibabacloud.com/v1beta1
kind: AdvancedHorizontalPodAutoscalerTemplate
metadata:
  name: ahpa-demo
spec:
  metrics:
  - type: Resource
    resource:
      name: rps
      target:
        type: Utilization
        averageUtilization: 10 # The RPS threshold is set to 10. 
  maxReplicas: 50 # The maximum number of replicated pods is set to 50. 
  minReplicas: 0 # The minimum number of replicated pods is set to 0. 
  prediction:
    quantile: 95 # The confidence level of prediction is set to 95%. 
    scaleUpForward: 180 # The time range of forward prediction is set to 180 seconds. 
# The number of replicated pods is limited by the maximum number of replicated pods and the minimum number of replicated pods defined by AHPA from 00:00:00 on June 1, 2023 to 00:00:00 on June 1, 2123. 
  instanceBounds:
  - startTime: "2023-06-01 00:00:00"
    endTime: "2123-06-01 00:00:00"
    bounds:
# The minimum number of replicated pods is 0 and the maximum number of replicated pods is 50 from 0 am to 6 am. 
    - cron: '* 0-6 ? * *'
      maxReplicas: 50
      minReplicas: 0
# The minimum number of replicated pods is 5 and the maximum number of replicated pods is 50 from 7 am to 9 am. 
    - cron: '* 7-9 ? * *'
      maxReplicas: 50
      minReplicas: 5
# The minimum number of replicated pods is 10 and the maximum number of replicated pods is 50 from 10 am to 4 pm. 
    - cron: '* 10-16 ? * *'
      maxReplicas: 50
      minReplicas: 10
# The minimum number of replicated pods is 2 and the maximum number of replicated pods is 50 from 5 pm to 11 pm. 
    - cron: '* 17-23 ? * *'
      maxReplicas: 50
      minReplicas: 2

Fields used in cron expressions

The following table describes the fields that are contained in a CRON expression. For more information, see Cron expressions.

Special characters used in cron expressions:

• An asterisk (*) indicates any value. For example, * indicates any minute or hour.

• A forward slash (/) indicates the step size. For example, /5 indicates five time units.

• Commas (,) are used as delimiters. For example, 1,3,5 indicates values 1, 3, and 5.

• Hyphens (-) are used in value ranges. For example, 1-5 indicates values 1 to 5.

• Question marks (?) are used only in the Day of month and Day of week fields to indicate variable values.

Step 2: Create a Knative Service and enable AHPA for the Service

After you enable AHPA, you can use AHPA through the Knative Service.

1. Log on to the ACK console. In the left-side navigation pane, click Clusters.

2. On the Clusters page, find the cluster that you want to manage and click its name. In the left-side navigation pane, choose Applications > Knative.

3. On the Services tab of the Knative page, set Namespace to default, click Create from Template, copy the following YAML content to the editor, and then click Create to create a Service named helloworld-go-demo.

   apiVersion: serving.knative.dev/v1
   kind: Service
   metadata:
     name: helloworld-go-demo
   spec:
     template:
       metadata:
         annotations:
           autoscaling.knative.dev/class: ahpa.autoscaling.knative.dev # Specify the AHPA plug-in. 
           autoscaling.knative.dev.alibabacloud/ahpa-template: "ahpa-demo" # If you modify the AHPA template parameter, the corresponding revision is also updated. 
       spec:
         containers:
         - image: registry.cn-hangzhou.aliyuncs.com/knative-sample/helloworld-go:73fbdd56
           env:
           - name: TARGET
             value: "Knative"

   After the Service is created, record the gateway address and domain name of the Service, which will be used in Step 3: Access the Service.

   

Step 3: Access the Service

Run the following command to access the Service:

# helloworld-go-demo.default.example.com is the default domain name of the Service. 
# alb-i5lagvip6fga******.cn-shenzhen.alb.aliyuncs.com is the gateway address of the Service. 
curl -H "Host: helloworld-go-demo.default.example.com" http://alb-i5lagvip6fga******.cn-shenzhen.alb.aliyuncs.com

Expected output:

Hello Knative!

Step 4 (Optional): Verify scheduled scaling

On the Monitoring Dashboards of Knative, you can view the trends of pod scaling for the Knative Service. For more information about the Knative dashboard, see View the Knative monitoring dashboard.

References

You can configure auto scaling based on the number of concurrent pod requests and RPS configurations. For more information, see Enable auto scaling to withstand traffic fluctuations.