[🐛 Bug]: Selenium Grid Chart 0.42.1 Not Scaling Properly

[codercalum]

What happened?

On version 0.42.1 of the helm chart I can't fully auto-scale my nodes. If I start 30 long running requests some are always queued and never get allocated a new node.

kubectl get --raw \                                        
  "/apis/external.metrics.k8s.io/v1beta1/namespaces/default/s0-seleniumgrid-chrome?labelSelector=scaledobject.keda.sh/name=selenium-grid-selenium-node-chrome" \
  | jq

Checking the keda external metric is only returning the value for the number of sessions in the queue:

{
  "kind": "ExternalMetricValueList",
  "apiVersion": "external.metrics.k8s.io/v1beta1",
  "metadata": {},
  "items": [
    {
      "metricName": "s0-seleniumgrid-chrome",
      "metricLabels": null,
      "timestamp": "2025-04-26T18:12:38Z",
      "value": "7"
    }
  ]
}

I believe this is meant to be the number of sessions in the queue + ongoing sessions so that it scales to the required number of nodes? Is my understanding correct or am i missing something. I have tried exactly matching the browsers:

• browserName = "chrome"
• browserVersion = "" # Can be empty for any version according to the docs
• platformName = "linux"
• enableManagedDownloads = "true"

helm install selenium-grid docker-selenium/selenium-grid
--version 0.42.1 \
--values helm-chart.yaml

# Helm values.yaml for Selenium Grid
# Selenium Hub configuration
hub:
  # Resource requests/limits for Hub (1 CPU, 2816 MB RAM)
  resources:
    requests:
      cpu: "1"
      memory: "2816Mi"
    limits:
      cpu: "1"
      memory: "2816Mi"
  # Increase session request timeout to 600 seconds
  extraEnvironmentVariables:
    - name: SE_SESSION_REQUEST_TIMEOUT
      value: "600"

# Enable KEDA-based autoscaling for browser nodes
autoscaling:
  enableWithExistingKEDA: true
  scalingType: deployment            # Scale browser Deployments (not one-shot Jobs)
  scaledOptions:
    minReplicaCount: 2              # Minimum 2 Chrome nodes
    maxReplicaCount: 50             # Maximum 50 Chrome nodes
  terminationGracePeriodSeconds: 900 # 15 minute grace period for node shutdown
  scaledObjectOptions:
    platformName: linux

# Chrome Node (browser) configuration
chromeNode:
  deploymentEnabled: true   # Ensure Chrome node Deployment is created
  replicas: 2              # Start with 2 Chrome nodes (initial replicas)
  # Resource requests/limits for each Chrome node (0.8 CPU, 2048 MB RAM)
  resources:
    requests:
      cpu: "0.8"
      memory: "2048Mi"
    limits:
      cpu: "0.8"
      memory: "2048Mi"
  # Environment variables for Chrome node containers
  extraEnvironmentVariables:
    - name: SE_NODE_BROWSER_VERSION
      value: ""
    - name: SE_NODE_ENABLE_CDP
      value: "true"
    - name: SE_NODE_ENABLE_MANAGED_DOWNLOADS
      value: "true"
    - name: SE_NODE_MAX_SESSIONS
      value: "1"
    - name: SE_NODE_PLATFORM_NAME
      value: "linux"
    - name: SE_NODE_PORT
      value: "4444"
    - name: SE_VNC_NO_PASSWORD
      value: "true"

# Disable other browser nodes (only Chrome is used)
firefoxNode:
  enabled: false

edgeNode:
  enabled: false

Test Script in python:

import asyncio
import time
import concurrent.futures
from selenium import webdriver
from selenium.webdriver.chrome.options import Options

"""
Test script to run 100 browsers over time in parallel - see if selenium grid / porter scales up
"""


async def selenium_task(task_id):
    try:
        print(f"Starting task {task_id}")
        # Set up Chrome options
        chrome_options = Options()
        chrome_options.set_capability('platformName', 'linux')
        # chrome_options.set_capability('browserVersion', '135.0')
        chrome_options.enable_downloads = True

        # This will run in a separate thread to not block the event loop
        with concurrent.futures.ThreadPoolExecutor() as executor:
            # We'll use run_in_executor to run the blocking Selenium code in a separate threadpoetry run which python
            await asyncio.get_event_loop().run_in_executor(
                executor,
                selenium_function,
                task_id,
                chrome_options
            )

        print(f"Completed task {task_id}")
        return f"Result from task {task_id}"

    except Exception as e:
        print(f"Task {task_id} encountered an error: {e}")


def selenium_function(task_id, chrome_options):
    """The original selenium function, slightly modified to show which task is running"""
    print(f"Task {task_id}: Creating driver")
    # Connect to Selenium Grid at the provided URL
    driver = webdriver.Remote(
        command_executor="http://localhost:4444/wd/hub",
        options=chrome_options,
        keep_alive=True  # Maintain the session
    )

    try:
        # Navigate to Google
        print(f"Task {task_id}: Navigating to Google")
        driver.get("https://www.google.com")
        print(f"Task {task_id}: Sleeping at google...")

        for i in range(20):
            driver.get("https://www.google.com")
            time.sleep(100)

        # Print the page title
        print(f"Task {task_id}: Page title is: {driver.title}")
        return driver.title
    finally:
        print(f"Task {task_id}: Closing driver")
        driver.quit()


async def main():
    # Create a list to hold the tasks
    tasks = []

    # Start 6 tasks, one every 2 seconds
    for i in range(35):
        task = asyncio.create_task(selenium_task(i + 1))
        tasks.append(task)
        print(f"Scheduled task {i + 1}")

        # Wait 2 seconds before starting the next task
        await asyncio.sleep(1)

    # Wait for all tasks to complete
    print("Waiting for all tasks to complete...")
    results = await asyncio.gather(*tasks)

    print("All tasks completed!")
    print("Results:", results)


if __name__ == "__main__":
    # Run the async main function
    asyncio.run(main())

Example output from a curl:

curl --location 'http://localhost:4444/graphql' \
--header 'Content-Type: application/json' \
--header 'Authorization: ••••••' \
--data '{"query":"{ grid { sessionCount, maxSession, totalSlots }, nodesInfo { nodes { id, status, sessionCount, maxSession, slotCount, stereotypes, sessions { id, capabilities, slot { stereotype } } } }, sessionsInfo { sessionQueueRequests } }","variables":{}}'

{
    "data": {
        "grid": {
            "sessionCount": 2,
            "maxSession": 2,
            "totalSlots": 2
        },
        "nodesInfo": {
            "nodes": [
                {
                    "id": "93060358-a27b-4a58-807e-aab18f557abb",
                    "status": "UP",
                    "sessionCount": 1,
                    "maxSession": 1,
                    "slotCount": 1,
                    "stereotypes": "[\n  {\n    \"slots\": 1,\n    \"stereotype\": {\n      \"browserName\": \"chrome\",\n      \"browserVersion\": \"\",\n      \"container:hostname\": \"selenium-grid-selenium-node-chrome-6c476c74cb-rmw7s\",\n      \"goog:chromeOptions\": {\n        \"binary\": \"\/usr\/bin\/google-chrome\"\n      },\n      \"platformName\": \"linux\",\n      \"se:containerName\": \"selenium-grid-selenium-node-chrome-6c476c74cb-rmw7s\",\n      \"se:downloadsEnabled\": true,\n      \"se:noVncPort\": 7900,\n      \"se:vncEnabled\": true\n    }\n  }\n]",
                    "sessions": [
                        {
                            "id": "c13d218a5d807e688953afee0a340935",
                            "capabilities": "{\n  \"acceptInsecureCerts\": false,\n  \"browserName\": \"chrome\",\n  \"browserVersion\": \"135.0.7049.84\",\n  \"chrome\": {\n    \"chromedriverVersion\": \"135.0.7049.84 (6c019e56001911b3fd467e03bf68c435924d62f4-refs\/branch-heads\/7049@{#1778})\",\n    \"userDataDir\": \"\/tmp\/.org.chromium.Chromium.QmrcjW\"\n  },\n  \"fedcm:accounts\": true,\n  \"goog:chromeOptions\": {\n    \"debuggerAddress\": \"localhost:37491\"\n  },\n  \"networkConnectionEnabled\": false,\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"proxy\": {\n  },\n  \"se:bidiEnabled\": false,\n  \"se:cdp\": \"ws:\/\/selenium-grid-selenium-hub.default\/session\/c13d218a5d807e688953afee0a340935\/se\/cdp\",\n  \"se:cdpVersion\": \"135.0.7049.84\",\n  \"se:containerName\": \"selenium-grid-selenium-node-chrome-6c476c74cb-rmw7s\",\n  \"se:downloadsEnabled\": true,\n  \"se:noVncPort\": 7900,\n  \"se:vnc\": \"ws:\/\/selenium-grid-selenium-hub.default\/session\/c13d218a5d807e688953afee0a340935\/se\/vnc\",\n  \"se:vncEnabled\": true,\n  \"se:vncLocalAddress\": \"ws:\/\/10.76.20.19:7900\",\n  \"setWindowRect\": true,\n  \"strictFileInteractability\": false,\n  \"timeouts\": {\n    \"implicit\": 0,\n    \"pageLoad\": 300000,\n    \"script\": 30000\n  },\n  \"unhandledPromptBehavior\": \"dismiss and notify\",\n  \"webauthn:extension:credBlob\": true,\n  \"webauthn:extension:largeBlob\": true,\n  \"webauthn:extension:minPinLength\": true,\n  \"webauthn:extension:prf\": true,\n  \"webauthn:virtualAuthenticators\": true\n}",
                            "slot": {
                                "stereotype": "{\n  \"browserName\": \"chrome\",\n  \"browserVersion\": \"\",\n  \"container:hostname\": \"selenium-grid-selenium-node-chrome-6c476c74cb-rmw7s\",\n  \"goog:chromeOptions\": {\n    \"binary\": \"\/usr\/bin\/google-chrome\"\n  },\n  \"platformName\": \"linux\",\n  \"se:containerName\": \"selenium-grid-selenium-node-chrome-6c476c74cb-rmw7s\",\n  \"se:downloadsEnabled\": true,\n  \"se:noVncPort\": 7900,\n  \"se:vncEnabled\": true\n}"
                            }
                        }
                    ]
                },
                {
                    "id": "d551c4b4-1628-4d8c-889a-1d51ed2a6b09",
                    "status": "UP",
                    "sessionCount": 1,
                    "maxSession": 1,
                    "slotCount": 1,
                    "stereotypes": "[\n  {\n    \"slots\": 1,\n    \"stereotype\": {\n      \"browserName\": \"chrome\",\n      \"browserVersion\": \"\",\n      \"container:hostname\": \"selenium-grid-selenium-node-chrome-6c476c74cb-r6blq\",\n      \"goog:chromeOptions\": {\n        \"binary\": \"\/usr\/bin\/google-chrome\"\n      },\n      \"platformName\": \"linux\",\n      \"se:containerName\": \"selenium-grid-selenium-node-chrome-6c476c74cb-r6blq\",\n      \"se:downloadsEnabled\": true,\n      \"se:noVncPort\": 7900,\n      \"se:vncEnabled\": true\n    }\n  }\n]",
                    "sessions": [
                        {
                            "id": "9bc102271cc7b223c9773140ff17c7cd",
                            "capabilities": "{\n  \"acceptInsecureCerts\": false,\n  \"browserName\": \"chrome\",\n  \"browserVersion\": \"135.0.7049.84\",\n  \"chrome\": {\n    \"chromedriverVersion\": \"135.0.7049.84 (6c019e56001911b3fd467e03bf68c435924d62f4-refs\/branch-heads\/7049@{#1778})\",\n    \"userDataDir\": \"\/tmp\/.org.chromium.Chromium.ODftnE\"\n  },\n  \"fedcm:accounts\": true,\n  \"goog:chromeOptions\": {\n    \"debuggerAddress\": \"localhost:38639\"\n  },\n  \"networkConnectionEnabled\": false,\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"proxy\": {\n  },\n  \"se:bidiEnabled\": false,\n  \"se:cdp\": \"ws:\/\/selenium-grid-selenium-hub.default\/session\/9bc102271cc7b223c9773140ff17c7cd\/se\/cdp\",\n  \"se:cdpVersion\": \"135.0.7049.84\",\n  \"se:containerName\": \"selenium-grid-selenium-node-chrome-6c476c74cb-r6blq\",\n  \"se:downloadsEnabled\": true,\n  \"se:noVncPort\": 7900,\n  \"se:vnc\": \"ws:\/\/selenium-grid-selenium-hub.default\/session\/9bc102271cc7b223c9773140ff17c7cd\/se\/vnc\",\n  \"se:vncEnabled\": true,\n  \"se:vncLocalAddress\": \"ws:\/\/10.76.20.20:7900\",\n  \"setWindowRect\": true,\n  \"strictFileInteractability\": false,\n  \"timeouts\": {\n    \"implicit\": 0,\n    \"pageLoad\": 300000,\n    \"script\": 30000\n  },\n  \"unhandledPromptBehavior\": \"dismiss and notify\",\n  \"webauthn:extension:credBlob\": true,\n  \"webauthn:extension:largeBlob\": true,\n  \"webauthn:extension:minPinLength\": true,\n  \"webauthn:extension:prf\": true,\n  \"webauthn:virtualAuthenticators\": true\n}",
                            "slot": {
                                "stereotype": "{\n  \"browserName\": \"chrome\",\n  \"browserVersion\": \"\",\n  \"container:hostname\": \"selenium-grid-selenium-node-chrome-6c476c74cb-r6blq\",\n  \"goog:chromeOptions\": {\n    \"binary\": \"\/usr\/bin\/google-chrome\"\n  },\n  \"platformName\": \"linux\",\n  \"se:containerName\": \"selenium-grid-selenium-node-chrome-6c476c74cb-r6blq\",\n  \"se:downloadsEnabled\": true,\n  \"se:noVncPort\": 7900,\n  \"se:vncEnabled\": true\n}"
                            }
                        }
                    ]
                }
            ]
        },
        "sessionsInfo": {
            "sessionQueueRequests": [
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}",
                "{\n  \"browserName\": \"chrome\",\n  \"goog:chromeOptions\": {\n    \"extensions\": [\n    ],\n    \"args\": [\n    ]\n  },\n  \"pageLoadStrategy\": \"normal\",\n  \"platformName\": \"linux\",\n  \"se:downloadsEnabled\": true\n}"
            ]
        }
    }
}

Relevant log output

No log output

Operating System

GKE - Linux Machines

Docker Selenium version (image tag)

4.31.0-20250414

Selenium Grid chart version (chart version)

0.42.1

[github-actions]

@codercalum, thank you for creating this issue. We will troubleshoot it as soon as we can.

---

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Thank you!

[VietND96]

It looks like you didn't use latest KEDA core version

[codercalum]

Thanks @VietND96 !

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.