Configuring a FederatedHPA to Control the Scaling Rate

Why Do I Need to Control the Scaling Rate?

To limit the rate at which pods are scaled by the HPA controller, a scale-out needs to be fast, and a scale-in needs to be slow. However, if only the stabilization window is configured, the scaling rate cannot be limited after the stabilization window expires. To accurately and flexibly limit the scaling rate, you can configure the behavior section of the spec in the YAML file. In the behavior section, the scaling rate can be unique for each FederatedHPA, and different rates can be configured for scale-out and scale-in operations.

Procedure

The following describes behavior structures in common service scenarios. In other service scenarios, for example, if you want to perform slow scale-out or fast scale-in, you can set scaleUp and scaleDown under the behavior field by referring to the following description of each behavior structure.

• Scenario 1: Fast scale-out

  If you want to perform a fast scale-out at peak hours, you can set Percent to a large value.

  behavior: 
    scaleUp: 
      policies: 
      - type: Percent 
        value: 900 
        periodSeconds: 60

  In this example, the value of Percent is 900. This means the scaling rate increases tenfold (1 + 900%) in each scaling period. For example, if the number of pods in a workload starts from 1, the number of pods added every 60 seconds changes as follows: 1 > 10 > 100 > ... . Note that the number of pods after a scale-out cannot exceed the maximum number of pods configured in the FederatedHPA.

  Resource consumption of the Percent type fluctuates greatly. If you want the resource consumption to be controllable, use the Pods type with the absolute value.

  behavior: 
    scaleDown: 
      policies: 
      - type: Pods 
        value: 10 
        periodSeconds: 60

  In this example, the value of Pods is 10. This means 10 pods are added in each scaling period. For example, if the number of pods in a workload starts from 1, the number of pods added every 60 seconds changes as follows: 1 > 11 > 21 > ... . Note that the number of pods after a scale-out cannot exceed the maximum number of pods configured in the FederatedHPA.

• Scenario 2: Slow scale-in

  If you want to scale in pods in a workload more slowly after peak hours to improve application reliability, you can set Pods to a small value and periodSeconds to a large value.

  behavior: 
    scaleDown: 
      policies: 
      - type: Pods 
        value: 1 
        periodSeconds: 600

  In this example, the value of Pods is 1, and the value of periodSeconds is 600. This means the scale-in period is 600 seconds, and one pod is reduced for each scale-in. If the initial number of pods is 100, the number of pods to be scaled in every 600 seconds changes as follows: 100 > 99 > 98 > … . In extreme cases, if you do not want the pods in a workload to be automatically scaled in, you can set Percent or Pods to 0.

• Scenario 3: Default scaling rate

  If behavior is not configured, the default settings of the FederatedHPA are as follows:

  behavior: 
    scaleDown: 
      stabilizationWindowSeconds: 300 
      policies: 
      - type: Percent 
        value: 100 
        periodSeconds: 15 
    scaleUp: 
      stabilizationWindowSeconds: 0 
      policies: 
      - type: Percent 
        value: 100 
        periodSeconds: 15 
      - type: Pods 
        value: 4 
        periodSeconds: 15 

  In the default configuration, the scaling period is 15 seconds. In each scaling period, a scale-out or scale-in is performed at a rate of twice (1 + 100%). 4 pods to be scaled each time.