Selenium Grid Scaler

Selenium Grid Scaler ^{Click here for latest}

Scales Selenium browser nodes based on number of requests waiting in session queue

Availability: v2.4+ Maintainer: Volvo Cars

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Trigger Specification

This specification describes the selenium-grid trigger that scales browser nodes based on number of requests in session queue and the max sessions per grid.

The scaler creates one browser node per pending request in session queue, divided by the max amount of sessions that can run in parallel. You will have to create one trigger per browser capability that you would like to support in your Selenium Grid.

The below is an example trigger configuration for chrome node.

triggers:
  - type: selenium-grid
    metadata:
      url: 'http://selenium-hub:4444/graphql' # Required
      browserName: 'chrome'  # Required
      browserVersion: '91.0' # Optional. Only required when supporting multiple versions of browser in your Selenium Grid.
      unsafeSsl : 'true' # Optional
      activationThreshold: 5 # Optional

Parameter list:

url - Graphql url of your Selenium Grid. Refer to the Selenium Grid’s documentation here to for more info.
browserName - Name of browser that usually gets passed in the browser capability. Refer to the Selenium Grid’s and WebdriverIO’s documentation for more info.
sessionBrowserName - Name of the browser when it is an active session, only set if BrowserName changes between the queue and the active session. See the Edge example below for further detail. (Optional)
browserVersion - Version of browser that usually gets passed in the browser capability. Refer to the Selenium Grid’s and WebdriverIO’s documentation for more info. (Optional)
unsafeSsl - Skip certificate validation when connecting over HTTPS. (Values: true, false, Default: false, Optional)
activationThreshold - Target value for activating the scaler. Learn more about activation here. (Default: 0, Optional)

Example

Here is a full example of scaled object definition using Selenium Grid trigger:

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: selenium-grid-chrome-scaledobject
  namespace: keda
  labels:
    deploymentName: selenium-chrome-node
spec:
  maxReplicaCount: 8
  scaleTargetRef:
    name: selenium-chrome-node
  triggers:
    - type: selenium-grid
      metadata:
        url: 'http://selenium-hub:4444/graphql'
        browserName: 'chrome'

The above example will create Chrome browser nodes equal to the requests pending in session queue for Chrome browser.

Similarly for Firefox

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: selenium-grid-firefox-scaledobject
  namespace: keda
  labels:
    deploymentName: selenium-firefox-node
spec:
  maxReplicaCount: 8
  scaleTargetRef:
    name: selenium-firefox-node
  triggers:
    - type: selenium-grid
      metadata:
        url: 'http://selenium-hub:4444/graphql'
        browserName: 'firefox'

Similarly for Edge. Note that for Edge you must set the sessionBrowserName to msedge inorder for scaling to work properly.

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: selenium-grid-edge-scaledobject
  namespace: keda
  labels:
    deploymentName: selenium-edge-node
spec:
  maxReplicaCount: 8
  scaleTargetRef:
    name: selenium-edge-node
  triggers:
    - type: selenium-grid
      metadata:
        url: 'http://selenium-hub:4444/graphql'
        browserName: 'MicrosoftEdge'
        sessionBrowserName: 'msedge'

If you are supporting multiple versions of browser capability in your Selenium Grid, You should create one scaler for every browser version and pass the browserVersion in the metadata.

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: selenium-grid-chrome-91-scaledobject
  namespace: keda
  labels:
    deploymentName: selenium-chrome-node-91
spec:
  maxReplicaCount: 8
  scaleTargetRef:
    name: selenium-chrome-node-91
  triggers:
    - type: selenium-grid
      metadata:
        url: 'http://selenium-hub:4444/graphql'
        browserName: 'chrome'
        browserVersion: '91.0'

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: selenium-grid-chrome-90-scaledobject
  namespace: keda
  labels:
    deploymentName: selenium-chrome-node-90
spec:
  maxReplicaCount: 8
  scaleTargetRef:
    name: selenium-chrome-node-90
  triggers:
    - type: selenium-grid
      metadata:
        url: 'http://selenium-hub:4444/graphql'
        browserName: 'chrome'
        browserVersion: '90.0'