kubevela.github.io/auto-scaler.md at deaa6a87dba611a1966dbf801c0d876674c8ddb1

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Auto Scaling

KubeVela supports integrate any auto-scaling ways in Kubernetes world. In this doc, we'll use KEDA for auto-scaling. KEDA is a Kubernetes-based Event Driven Autoscaling component, it provides event driven scale for any container running in Kubernetes.

Enable the addon

vela addon enable keda

After installed, you'll get the keda-auto-scaler trait, you can learn the specification below.

Use keda-auto-scaler in Application

Keda supports lots of triggers such as cron, cpu, etc, let's check some examples to learn how it works in KubeVela.

:::caution When you're using HPA, you must specify the apply-once policy to let the HPA control the replica field. :::

How it works with Trigger?

Here're several examples about how autoscaling work in KubeVela application.

Cron HPA

We can use cron hpa with the keda cron trigger.

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: scaler-eg-app
spec:
  components:
    - name: hello-world-scaler
      type: webservice
      properties:
        image: oamdev/hello-world
        ports:
         - port: 8000
           expose: true        
      traits:
        # This Trait used for initializing the replica
        - type: scaler
          properties:
            replicas: 1
        - type: keda-auto-scaler
          properties:
            triggers:
            - type: cron
              metadata:
                timezone: Asia/Hong_Kong  # The acceptable values would be a value from the IANA Time Zone Database.
                start: 00 * * * *       # Every hour on the 30th minute
                end: 10 * * * *         # Every hour on the 45th minute
                desiredReplicas: "3"

  policies:
    - name: apply-once
      type: apply-once
      properties:
        enable: true
        rules:
        - strategy:
            path: ["spec.replicas"]
          selector:
            resourceTypes: ["Deployment"]

In this example, it will scale up to 3 replicas from 0-10 in every hour. After that, it will scale back to the initial replica 1.

CPU based HPA

We can use CPU based hpa with the keda cpu trigger.

:::tip You must follow the prerequisite of this keda trigger:

KEDA uses standard cpu and memory metrics from the Kubernetes Metrics Server, which is not installed by default on certain Kubernetes deployments such as EKS on AWS. Additionally, the resources section of the relevant Kubernetes Pods must include limits (at a minimum). :::

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: scaler-eg-app
spec:
  components:
    - name: frontend
      type: webservice
      properties:
        image: oamdev/testapp:v1
        cmd: ["node", "server.js"]
        cpu: "0.1"
        ports:
          - port: 8080
            expose: true
      traits:
        # This Trait used for initializing the replica
        - type: scaler
          properties:
            replicas: 1
        - type: gateway
          properties:
            class: traefik
            classInSpec: true
            domain: test.my.domain
            http:
              "/": 8080
        - type: keda-auto-scaler
          properties:
            minReplicaCount: 1
            maxReplicaCount: 10
            cooldownPeriod: 10
            pollingInterval: 10
            triggers:
            - type: cpu
              metricType: Utilization
              metadata:
                value: "80"
  policies:
    - name: apply-once
      type: apply-once
      properties:
        enable: true
        rules:
        - strategy:
            path: ["spec.replicas"]
          selector:
            resourceTypes: ["Deployment"]

In this example, we also exposed the service entrypoint by using the gateway trait, make sure you have the traefik ingress controller if you're not using velad.

We can get the endpoint by the following command.

$ vela status scaler-eg-app --endpoint
  Please access scaler-eg-app from the following endpoints:
  +---------+-----------+--------------------------+------------------------------+-------+
  | CLUSTER | COMPONENT | REF(KIND/NAMESPACE/NAME) |           ENDPOINT           | INNER |
  +---------+-----------+--------------------------+------------------------------+-------+
  | local   | frontend  | Service/default/frontend | http://frontend.default:8080 | true  |
  | local   | frontend  | Ingress/default/frontend | http://test.my.domain        | false |
  +---------+-----------+--------------------------+------------------------------+-------+

Please configure the /etc/hosts for visit the service:

echo "<IP of your service>   test.my.domain" >> /etc/hosts

Then we can add CPU pressure by using the ab tool.

ab -n 300000 -c 200  http://test.my.domain/

We can use vela top to check the replica changing during the ab test.

Other Triggers

All of the triggers are supported and the trigger part spec in KubeVela keda-auto-scaler trait are all aligned with KEDA trigger, you can refer to the docs of keda to learn details.

Specify the Applied Workload

If your component is webservice which actually using Kubernetes Deployment as the underlying workload, you don't need to specify the workload type.

If you're using helm or customized component types, you should specify the scaleTargetRef field to tell the trait which workload it should work with.

KEDA supports Deployment, StatefulSet and Custom Resource, the only constraint is that the target Custom Resource must define /scale subresource.

Specification of `keda-auto-scaler`

Name	Description	Type	Required	Default
triggers		[]triggers	true
scaleTargetRef		scaleTargetRef	true
pollingInterval	specify the polling interval of metrics, Default: 30 seconds.	int	false	30
cooldownPeriod	Specify the cool down period that prevents the scaler from scaling down after each trigger activation. Default: 60 seconds.	int	false	60
idleReplicaCount	Specify the idle period that the scaler to scale to zero. Default: ignored, must be less than minReplicaCount.	int	false	0
minReplicaCount	Specify the minimal replica count. Default: 0.	int	false	1
maxReplicaCount	Specify the maximal replica count. Default: 100.	int	false	100
fallback	Specify the fallback value when the metrics server is not available.	fallback	true

triggers

Name	Description	Type	Required	Default
type	specify the type of trigger, the rest spec here aligns with KEDA spec.	string	true
metadata	specify the metadata of trigger, the spec aligns with the spec of KEDA https://keda.sh/docs/2.8/scalers/.	map[string]_	true

scaleTargetRef

Name	Description	Type	Required	Default
apiVersion	Specify apiVersion for target workload.	string	false	apps/v1
kind	Specify kind for target workload.	string	false	Deployment
envSourceContainerName	Specify containerName, default to find this path ".spec.template.spec.containers[0]".	string	false	empty
name	Specify the instance name for target workload.	string	true

fallback

Name	Description	Type	Required	Default
failureThreshold	Specify the failure threshold of the scaler. Default: 3.	int	false	3
replicas	Specify the replica when failed to get metrics. Default to minReplicaCount.	int	false	1

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