Integrate Selenium Grid with Azure DevOps

Selenium Grid lets you run tests across multiple browsers and operating systems in parallel. Integrating it with Azure DevOps gives you scalable, parallel cross-browser test execution in CI without paying for a cloud testing platform.

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Selenium Grid architecture in Azure DevOps

Azure Pipeline Agent
       │
       ▼
Docker Compose (on the agent)
  ├── Selenium Hub      (distributes sessions)
  ├── Chrome Node 1     (runs Chrome tests)
  ├── Chrome Node 2     (parallel Chrome)
  └── Firefox Node      (runs Firefox tests)
       │
       ▼
Test code connects to Hub → Hub routes to available Node

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Docker Compose for Selenium Grid

YAML
1# docker-compose.selenium-grid.yml
2version: "3"
3services:
4  selenium-hub:
5    image: selenium/hub:4.21.0
6    container_name: selenium-hub
7    ports:
8      - "4444:4444"
9    environment:
10      - SE_NODE_MAX_SESSIONS=4
11
12  chrome-node-1:
13    image: selenium/node-chrome:4.21.0
14    shm_size: '2gb'
15    depends_on:
16      - selenium-hub
17    environment:
18      - SE_EVENT_BUS_HOST=selenium-hub
19      - SE_EVENT_BUS_PUBLISH_PORT=4442
20      - SE_EVENT_BUS_SUBSCRIBE_PORT=4443
21      - SE_NODE_MAX_SESSIONS=2
22      - SE_VNC_NO_PASSWORD=1
23
24  chrome-node-2:
25    image: selenium/node-chrome:4.21.0
26    shm_size: '2gb'
27    depends_on:
28      - selenium-hub
29    environment:
30      - SE_EVENT_BUS_HOST=selenium-hub
31      - SE_EVENT_BUS_PUBLISH_PORT=4442
32      - SE_EVENT_BUS_SUBSCRIBE_PORT=4443
33
34  firefox-node:
35    image: selenium/node-firefox:4.21.0
36    shm_size: '2gb'
37    depends_on:
38      - selenium-hub
39    environment:
40      - SE_EVENT_BUS_HOST=selenium-hub
41      - SE_EVENT_BUS_PUBLISH_PORT=4442
42      - SE_EVENT_BUS_SUBSCRIBE_PORT=4443

---

Connecting tests to the Grid

JAVA
1// Java WebDriver connecting to Grid
2ChromeOptions options = new ChromeOptions();
3options.addArguments("--no-sandbox");
4
5WebDriver driver = new RemoteWebDriver(
6    new URL("http://localhost:4444/wd/hub"),
7    options
8);

PYTHON
1# Python WebDriver connecting to Grid
2from selenium import webdriver
3from selenium.webdriver.chrome.options import Options
4
5options = Options()
6options.add_argument("--no-sandbox")
7
8driver = webdriver.Remote(
9    command_executor="http://localhost:4444/wd/hub",
10    options=options
11)

---

Azure Pipelines YAML

YAML
1trigger:
2  branches:
3    include: [main]
4
5pool:
6  name: Self-Hosted-Linux   # Self-hosted agent with Docker installed
7  # Microsoft-hosted agents don't persist Docker between steps — use self-hosted
8
9steps:
10  - script: |
11      docker-compose -f docker-compose.selenium-grid.yml up -d
12      echo "Waiting for Grid to be ready..."
13      timeout 60 bash -c 'until curl -s http://localhost:4444/wd/hub/status | grep -q "ready.*true"; do sleep 2; done'
14    displayName: Start Selenium Grid
15
16  - task: JavaToolInstaller@0
17    inputs:
18      versionSpec: '17'
19      jdkArchitectureOption: x64
20      jdkSourceOption: PreInstalled
21
22  - script: |
23      mvn test \
24        -DGRID_URL=http://localhost:4444/wd/hub \
25        -DBASE_URL=$(STAGING_URL) \
26        -Dsurefire.failIfNoSpecifiedTests=false
27    displayName: Run cross-browser tests
28
29  - task: PublishTestResults@2
30    inputs:
31      testResultsFormat: JUnit
32      testResultsFiles: '**/surefire-reports/TEST-*.xml'
33      testRunTitle: Selenium Grid — $(Build.BuildNumber)
34      mergeTestResults: true
35    condition: always()
36
37  - script: docker-compose -f docker-compose.selenium-grid.yml down -v
38    displayName: Stop Selenium Grid
39    condition: always()

---

Running tests in parallel across browsers

JAVA
1// TestNG parallel execution across browsers
2@DataProvider(name = "browsers", parallel = true)
3public Object[][] browsers() {
4    return new Object[][] {
5        { "chrome" },
6        { "firefox" },
7    };
8}
9
10@Test(dataProvider = "browsers")
11public void checkoutTest(String browserName) throws MalformedURLException {
12    MutableCapabilities caps;
13    if ("chrome".equals(browserName)) {
14        caps = new ChromeOptions();
15    } else {
16        caps = new FirefoxOptions();
17    }
18    
19    WebDriver driver = new RemoteWebDriver(
20        new URL("http://localhost:4444/wd/hub"), caps
21    );
22    // Run test...
23    driver.quit();
24}

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Common errors and fixes

Error: Grid hub starts but nodes don't register Fix: Nodes register via the event bus on ports 4442/4443. Ensure these ports are exposed and the SE_EVENT_BUS_HOST env var points to the hub service name (not localhost).

Error: "No such session" errors during parallel execution Fix: Sessions are per-driver instance. Don't share WebDriver instances across threads. Create a new driver per test method.

Error: shm_size has no effect and Chrome crashes Fix: Add --disable-dev-shm-usage to Chrome options. In Docker, /dev/shm is limited to 64MB by default — Chrome needs more for rendering. The option disables shared memory use.

Error: Grid shows nodes as available but tests queue indefinitely Fix: Check SE_NODE_MAX_SESSIONS on each node. If set too low, requests queue. Set to match available CPU cores (2 sessions per CPU core is a good rule).