Exercise - Deploy a scale object into your Azure Kubernetes Service cluster

  • 10 minutes

In this exercise, you'll deploy a scale object custom resource definition (CRD) into your AKS cluster. The scaler object contains the trigger that connects your deployed application to KEDA. After deploying to AKS, KEDA monitors the Redis List and scales up if the list length exceeds the defined threshold and scales down if the list length falls below the defined threshold.

ScaledObject manifest overview

  • scaleTargetRef: This section describes which workload KEDA observes.

      scaleTargetRef:
    apiVersion: apps/v1                           # Optional. Default: apps/v1
    kind: deployment                              # Optional. Default: Deployment
    name: contoso-microservice                    # Mandatory. Must be in the same namespace as the ScaledObject
    envSourceContainerName: contoso-microservice  # Optional. Default: .spec.template.spec.containers[0]

  • minReplicaCount and maxReplicaCount: These attributes determine the range of replicas KEDA uses for scaling. In this case, you instruct KEDA to scale from a minimum of zero to a max of 20.

      minReplicaCount: 0            # Optional. Default: 0
  maxReplicaCount: 20           # Optional. Default: 100

    Note

    minReplicaCount: 0 takes the Deployment default replica count from one to zero. This occurs if the service is idle and not processing any events. In this case, if there are no items in the Redis List, and the service remains idle, KEDA scales to zero.

  • advanced: This section is related to advanced customizations of KEDA. The restoreToOriginalReplicaCount instructs KEDA to return the replica count to the original value after scale-up events. In this case, you set it to false, which causes a scale down to the minReplicaCount value of zero.

      restoreToOriginalReplicaCount: false        # Optional. Default: false
  horizontalPodAutoscalerConfig:              # Optional. Section to specify HPA related options
    behavior:                                 # Optional. Use to modify HPA's scaling behavior
      scaleDown:
        stabilizationWindowSeconds: 300
        policies:
        - type: Percent
          value: 100
          periodSeconds: 15

  • triggers: This section uses scalers to detect if the object should be activated or deactivated and feed custom metrics for specific event sources. The listLength metric instructs KEDA to scale up when there are ten items in the list.

      triggers:
  - type: redis
    metadata:
      # address:                  # Format must be host:port
      passwordFromEnv: REDIS_KEY
      listName: keda              # Required
      listLength: "10"            # Required
      enableTLS: "false"          # optional
      databaseIndex: "0"          # optional
      hostFromEnv: REDIS_HOST
      portFromEnv: REDIS_PORT

For more information, see KEDA Scalers.

Create the ScaledObject manifest

  1. In Cloud Shell, create a manifest file for the Kubernetes Deployment called scaled-object.yaml using the touch command:

    touch scaled-object.yaml

  2. Open the integrated editor in Cloud Shell by entering code .

  3. Open the scaled-object.yaml file and add the following code section of YAML:

    apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: scaled-contoso
spec:
  scaleTargetRef:
    apiVersion: apps/v1                             # Optional. Default: apps/v1
    kind: deployment                                # Optional. Default: Deployment
    name: contoso-microservice                      # Mandatory. Must be in the same namespace as the ScaledObject
    envSourceContainerName: contoso-microservice    # Optional. Default: .spec.template.spec.containers[0]
  pollingInterval: 30                               # Optional. Default: 30 seconds
  cooldownPeriod:  120                              # Optional. Default: 300 seconds
  minReplicaCount: 0                                # Optional. Default: 0
  maxReplicaCount: 20                               # Optional. Default: 100
  advanced:                                         # Optional. Section to specify advanced options
    restoreToOriginalReplicaCount: false            # Optional. Default: false
    horizontalPodAutoscalerConfig:                  # Optional. Section to specify HPA related options
      behavior:                                     # Optional. Use to modify HPA's scaling behavior
        scaleDown:
          stabilizationWindowSeconds: 300
          policies:
          - type: Percent
            value: 100
            periodSeconds: 15
  triggers:
  - type: redis
    metadata:
      # address:                  # Format must be host:port
      passwordFromEnv: REDIS_KEY
      listName: keda              # Required
      listLength: "10"            # Required
      enableTLS: "false"          # optional
      databaseIndex: "0"          # optional
      hostFromEnv: REDIS_HOST
      portFromEnv: REDIS_PORT

  4. Save the manifest file (CTRL + S) and close the editor(CTRL + Q).

Apply the manifest

  1. Deploy the manifest to your cluster using the kubectl apply command:

    kubectl apply -f ./scaled-object.yaml

    Your output should look similar to the following example output:

    scaledobject.keda.sh/scaled-contoso created

  2. Check the number of running pods using the kubectl get pods command:

    kubectl get pods

    Your output should look similar to the following example output, with one pod running:

    NAME                                  READY   STATUS    RESTARTS   AGE
contoso-microservice-794d98b5-4flvg   1/1     Running   0          2m1s

  3. Periodically run the kubectl get pods command to verify the Deployment is scaling the number of pods according to the backlog of work.

    Note

    If you have the Linux utility watch installed, you can use the watch kubectl get pods command to see the pods scale to process the Redis list items. If not, you can use the kubectl get pods -w command.

    Your output should look similar to the following example output:

      NAME                                  READY   STATUS    RESTARTS   AGE
  contoso-microservice-794d98b5-4flvg   1/1     Running   0          3m
  contoso-microservice-794d98b5-4jpxp   1/1     Running   0          3m
  contoso-microservice-794d98b5-4lw7b   1/1     Running   0          2m15s
  contoso-microservice-794d98b5-5fqj5   1/1     Running   0          3m
  contoso-microservice-794d98b5-5kdbw   1/1     Running   0          2m15s

After all the items are processed and the cooldownPeriod expires, you'll see that the number of pods is zero. This is because KEDA removed all running replicas and has no items left to process.