Scaling an application

kubectl scale

The kubectl scale command lets your instantaneously change the number of replicas you want to run your application.

To use kubectl scale, you specify the new number of replicas by setting the --replicas flag. For example, to scale my-app to four replicas, run the following command, substituting CONTROLLER for deployment, statefulset, or another controller object type:

kubectl scale CONTROLLER my-app --replicas 4

If successful, this command's output should be similar to deployment "my-app" scaled.

Next, run:

kubectl get CONTROLLER my-app

The output should look similar to the following:

NAME                  DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
my-app                4         4         4            4           15m

kubectl apply

You can use kubectl apply to apply a new configuration file to an existing controller object. kubectl apply is useful for making multiple changes to a resource, and may be useful for users who prefer to manage their resources in configuration files.

To scale using kubectl apply, the configuration file you supply should include a new number of replicas in the replicas field of the object's specification.

The following is an updated version of the configuration file for the example my-app object. The example shows a Deployment, so if you use another type of controller, such as a StatefulSet, change the kind accordingly. This example works best on a cluster with at least three Nodes.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: app
  template:
    metadata:
      labels:
        app: app
    spec:
      containers:
      - name: my-container
        image: us-docker.pkg.dev/google-samples/containers/gke/hello-app:2.0

In this file, the value of the replicas field is 3. When this configuration file is applied, the object my-app scales to three replicas.

To apply an updated configuration file, run the following command:

kubectl apply -f config.yaml

Next, run:

kubectl get CONTROLLER my-app

The output should look similar to the following:

NAME                  DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
my-app                3         3         3            3           15m

Console

To scale a workload in the Google Cloud console, perform the following steps:

1. Go to the Workloads page in the Google Cloud console.

   Go to Workloads

2. In the workloads list, click the name of the workload you want to scale.

3. Click list Actions > Scale > Edit replicas.

4. Enter the new number of Replicas for the workload.

5. Click Scale.

kubectl autoscale

kubectl autoscale creates a HorizontalPodAutoscaler (or HPA) object that targets a specified resource (called the scale target) and scales it as needed. The HPA periodically adjusts the number of replicas of the scale target to match the average CPU utilization that you specify.

When you use kubectl autoscale, you specify a maximum and minimum number of replicas for your application, as well as a CPU utilization target. For example, to set the maximum number of replicas to six and the minimum to four, with a CPU utilization target of 50% utilization, run the following command:

kubectl autoscale deployment my-app --max 6 --min 4 --cpu-percent 50

In this command, the --max flag is required. The --cpu-percent flag is the target CPU utilization over all the Pods. This command does not immediately scale the Deployment to six replicas, unless there is already a systemic demand.

After running kubectl autoscale, the HorizontalPodAutoscaler object is created and targets the application. When there is a change in load, the object increases or decreases the application's replicas.

To get a list of the HorizontalPodAutoscaler objects in your cluster, run:

kubectl get hpa

To see a specific HorizontalPodAutoscaler object in your cluster, run:

kubectl get hpa HPA_NAME

Replace HPA_NAME with the name of your HorizontalPodAutoscaler object.

To see the HorizontalPodAutoscaler configuration:

kubectl get hpa HPA_NAME -o yaml

The output of this command is similar to the following:

apiVersion: v1
items:
- apiVersion: autoscaling/v1
  kind: HorizontalPodAutoscaler
  metadata:
    creationTimestamp: ...
    name: HPA_NAME
    namespace: default
    resourceVersion: "664"
    selfLink: ...
    uid: ...
  spec:
    maxReplicas: 10
    minReplicas: 1
    scaleTargetRef:
      apiVersion: apps/v1
      kind: Deployment
      name: HPA_NAME
    targetCPUUtilizationPercentage: 50
  status:
    currentReplicas: 0
    desiredReplicas: 0
kind: List
metadata: {}
resourceVersion: ""
selfLink: ""

In this example output, the targetCPUUtilizationPercentage field holds the 50 percentage value passed in from the kubectl autoscale example.

To see a detailed description of a specific HorizontalPodAutoscaler object in the cluster:

kubectl describe hpa HPA_NAME

You can modify the HorizontalPodAutoscaler by applying a new configuration file with kubectl apply, using kubectl edit, or using kubectl patch.

To delete a HorizontalPodAutoscaler object:

kubectl delete hpa HPA_NAME

Console

To autoscale a Deployment, perform the following steps:

1. Go to the Workloads page in the Google Cloud console.

   Go to Workloads

2. In the workloads list, click the name of the Deployment you want to autoscale.

3. Click list Actions > Autoscale.

4. Enter the Maximum number of replicas and, optionally, the Minimum number of replicas for the Deployment.

5. Under Autoscaling metrics, select and configure metrics as desired.

6. Click Autoscale.