Shows how to scale in Kubernetes apps in a deterministic and controlled way by specifying which pods to delete.

Minikube - CloneSet

# minikube version
minikube version
minikube version: v1.11.0
commit: 57e2f55f47effe9ce396cea42a1e0eb4f611ebbd

# Kubernetes version
kubectl version
Client Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.3", GitCommit:"2e7996e3e2712684bc73f0dec0200d64eec7fe40", GitTreeState:"clean", BuildDate:"2020-05-21T14:51:23Z", GoVersion:"go1.14.3", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.3", GitCommit:"2e7996e3e2712684bc73f0dec0200d64eec7fe40", GitTreeState:"clean", BuildDate:"2020-05-20T12:43:34Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}

# helm version
helm version
version.BuildInfo{Version:"v3.1.2", GitCommit:"d878d4d45863e42fd5cff6743294a11d28a9abce", GitTreeState:"clean", GoVersion:"go1.13.8"}

# start minikube
minikube start

# install kruise (give it a moment to initialise)
helm install kruise https://github.com/openkruise/kruise/releases/download/v0.5.0/kruise-chart.tgz

# deploy 6 replicas of nginx container using kruise CloneSet
cat <<EOF > test-app.yaml
apiVersion: apps.kruise.io/v1alpha1
kind: CloneSet
metadata:
  name: webapp
  labels:
    app: autoscaler-test
spec:
  replicas: 6
  selector:
    matchLabels:
      app: autoscaler-test
      tier: frontend
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: autoscaler-test
        tier: frontend
    spec:
      containers:
      - image: nginx
        name: nginx
EOF
kubectl apply -f test-app.yaml

# check that CloneSet and pods are running fine 
kubectl get clone
kubectl get pods

# select 3 pods to terminate, using awk to format pod names as yaml list, shuf to select random 3
pods=$(kubectl get pods -l "app=autoscaler-test" --no-headers | awk -F ' ' '{printf("     - %s\n",$1)}' | shuf -n 3)
echo "$pods"

# update the CloneSet - change replicas to 3 and add scaleStrategy/podsToDelete with a list of pods to delete (using $pods generated above)
cat <<EOF > test-app.yaml
apiVersion: apps.kruise.io/v1alpha1
kind: CloneSet
metadata:
  name: webapp
  labels:
    app: autoscaler-test
spec:
  replicas: 3
  scaleStrategy:
    podsToDelete:
$pods
  selector:
    matchLabels:
      app: autoscaler-test
      tier: frontend
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: autoscaler-test
        tier: frontend
    spec:
      containers:
      - image: nginx
        name: nginx
EOF
kubectl apply -f test-app.yaml

# you can verify that indeed only the selected 3 pods were deleted
kubectl get clone
kubectl get pods