http-add-on/docs/ref/v0.3.0/http_scaled_object.md

The HTTPScaledObject

This document reflects the specification of the HTTPScaledObject resource for the v0.3.0 version.

Each HTTPScaledObject looks approximately like the below:

kind: HTTPScaledObject
apiVersion: http.keda.sh/v1alpha1
metadata:
    name: xkcd
spec:
    host: "myhost.com"
    targetPendingRequests: 100
    scaleTargetRef:
        deployment: xkcd
        service: xkcd
        port: 8080

This document is a narrated reference guide for the HTTPScaledObject, and we'll focus on the spec field.

host

This is the host to apply this scaling rule to. All incoming requests with this value in their Host header will be forwarded to the Service and port specified in the below scaleTargetRef, and that same scaleTargetRef's Deployment will be scaled accordingly.

scaleTargetRef

This is the primary and most important part of the spec because it describes:

1. The incoming host to apply this scaling rule to.
2. What Deployment to scale.
3. The service to which to route HTTP traffic.

deployment

This is the name of the Deployment to scale. It must exist in the same namespace as this HTTPScaledObject and shouldn't be managed by any other autoscaling system. This means that there should not be any ScaledObject already created for this Deployment. The HTTP Add-on will manage a ScaledObject internally.

service

This is the name of the service to route traffic to. The add-on will create autoscaling and routing components that route to this Service. It must exist in the same namespace as this HTTPScaledObject and should route to the same Deployment as you entered in the deployment field.

port

This is the port to route to on the service that you specified in the service field. It should be exposed on the service and should route to a valid containerPort on the Deployment you gave in the deployment field.

targetPendingRequests

Default: 100

This is the number of pending (or in-progress) requests that your application needs to have before the HTTP Add-on will scale it. Conversely, if your application has below this number of pending requests, the HTTP add-on will scale it down.

For example, if you set this field to 100, the HTTP Add-on will scale your app up if it sees that there are 200 in-progress requests. On the other hand, it will scale down if it sees that there are only 20 in-progress requests. Note that it will never scale your app to zero replicas unless there are no requests in-progress. Even if you set this value to a very high number and only have a single in-progress request, your app will still have one replica.