Application autoscaling

A recent feature addition to Kubernetes is that of the Horizontal Pod Autoscaler. This resource type is really useful as it gives us a way to automatically set thresholds for scaling our application. Currently, that support is only for CPU, but there is alpha support for custom application metrics as well. 

Let's use the node-js-scaleReplicationController from the beginning of the chapter and add an autoscaling component. Before we start, let's make sure we are scaled back down to one replica using the following command:

$ kubectl scale --replicas=1 rc/node-js-scale

Now, we can create a Horizontal Pod Autoscaler, node-js-scale-hpa.yaml with the following hpa definition:

apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:
  name: node-js-scale
spec:
  minReplicas: 1
  maxReplicas: 3
  scaleTargetRef:
    apiVersion: v1
    kind: ReplicationController
    name: node-js-scale
  targetCPUUtilizationPercentage: 20

Go ahead and create this with thekubectl create...