Chapter 18. Pod Autoscaling

A horizontal pod autoscaler, defined by a HorizontalPodAutoscaler object, specifies how the system should automatically increase or decrease the scale of a replication controller or deployment configuration, based on metrics collected from the pods that belong to that replication controller or deployment configuration.

In order to use horizontal pod autoscalers, your cluster administrator must have properly configured cluster metrics.

The following metrics are supported by horizontal pod autoscalers:

After a horizontal pod autoscaler is created, it begins attempting to query Heapster for metrics on the pods. It may take one to two minutes before Heapster obtains the initial metrics.

After metrics are available in Heapster, the horizontal pod autoscaler computes the ratio of the current metric utilization with the desired metric utilization, and scales up or down accordingly. The scaling will occur at a regular interval, but it may take one to two minutes before metrics make their way into Heapster.

For replication controllers, this scaling corresponds directly to the replicas of the replication controller. For deployment configurations, scaling corresponds directly to the replica count of the deployment configuration. Note that autoscaling applies only to the latest deployment in the Complete phase.

To create a horizontal pod autoscaler, first define it in a file. For example:

apiVersion: extensions/v1beta1
kind: HorizontalPodAutoscaler
metadata:
  name: frontend-scaler 1
spec:
  scaleRef:
    kind: DeploymentConfig 2
    name: frontend 3
    apiVersion: v1 4
    subresource: scale
  minReplicas: 1 5
  maxReplicas: 10 6
  cpuUtilization:
    targetPercentage: 80 7

Save your definition to a file, such as scaler.yaml, then use the CLI to create the object:

$ oc create -f scaler.yaml

To view the status of a horizontal pod autoscaler:

$ oc get hpa
NAME              REFERENCE                                 TARGET    CURRENT   MINPODS        MAXPODS   AGE
frontend-scaler   DeploymentConfig/default/frontend/scale   80%       79%       1              10        8d

$ oc describe hpa frontend-scaler
Name:                           frontend-scaler
Namespace:                      default
Labels:                         <none>
CreationTimestamp:              Mon, 26 Oct 2015 21:13:47 -0400
Reference:                      DeploymentConfig/default/frontend/scale
Target CPU utilization:         80%
Current CPU utilization:        79%
Min pods:                       1
Max pods:                       10