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Version: v1.7

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

NameDescriptionTypeRequiredDefault
triggers[]triggerstrue
scaleTargetRefscaleTargetReftrue
pollingIntervalspecify the polling interval of metrics, Default: 30 seconds.intfalse30
cooldownPeriodSpecify the cool down period that prevents the scaler from scaling down after each trigger activation. Default: 60 seconds.intfalse60
idleReplicaCountSpecify the idle period that the scaler to scale to zero. Default: ignored, must be less than minReplicaCount.intfalse0
minReplicaCountSpecify the minimal replica count. Default: 0.intfalse1
maxReplicaCountSpecify the maximal replica count. Default: 100.intfalse100
fallbackSpecify the fallback value when the metrics server is not available.fallbacktrue

triggers

NameDescriptionTypeRequiredDefault
typespecify the type of trigger, the rest spec here aligns with KEDA spec.stringtrue
metadataspecify the metadata of trigger, the spec aligns with the spec of KEDA https://keda.sh/docs/2.8/scalers/.map[string]_true

scaleTargetRef

NameDescriptionTypeRequiredDefault
apiVersionSpecify apiVersion for target workload.stringfalseapps/v1
kindSpecify kind for target workload.stringfalseDeployment
envSourceContainerNameSpecify containerName, default to find this path ".spec.template.spec.containers[0]".stringfalseempty
nameSpecify the instance name for target workload.stringtrue

fallback

NameDescriptionTypeRequiredDefault
failureThresholdSpecify the failure threshold of the scaler. Default: 3.intfalse3
replicasSpecify the replica when failed to get metrics. Default to minReplicaCount.intfalse1