Docker Selenium Grid in Selenium Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Selenium Grid Node Registration Log

You have started a Selenium Grid node using Docker. The node logs show the following line:

"Registered a node with the hub: http://hub:4444"

What does this log line indicate?

A The node is running but has not yet attempted to connect to the hub.

B The node failed to connect to the hub due to network issues.

C The hub is down and the node is running standalone.

D The node has successfully connected and registered with the Selenium Grid hub.

💡 Hint

Look for keywords about registration and connection in the log line.

The log line explicitly states the node has registered with the hub URL, meaning the connection was successful.

❓ assertion

intermediate

Correct Assertion for Checking Node Availability

In a Selenium Grid test setup using Java, you want to assert that a remote WebDriver session is created successfully on a node. Which assertion is correct to verify the session is active?

Selenium Java

RemoteWebDriver driver = new RemoteWebDriver(new URL("http://hub:4444/wd/hub"), new ChromeOptions());
// Which assertion below correctly checks the session?

A assertEquals(driver.getSessionId(), null);

B assertTrue(driver.getSessionId().toString().isEmpty());

C assertNotNull(driver.getSessionId());

D assertFalse(driver.getSessionId() != null);

💡 Hint

A valid session ID means the session is active and not null.

The session ID is assigned when the session is created. Checking it is not null confirms the session exists.

🔧 Debug

advanced

Debugging Node Connection Failure in Docker Selenium Grid

You have a Docker Selenium Grid setup with one hub and two nodes. One node fails to register with the hub and logs show:

"Connection refused: connect"

What is the most likely cause?

A The node has incorrect browser version installed.

B The node container cannot reach the hub container due to network misconfiguration.

C The hub is running but has no available slots.

D The node's Docker image is outdated but still connects.

💡 Hint

Connection refused usually means no service is listening at the target address.

If the node cannot connect to the hub, it is often due to Docker network issues preventing communication between containers.

❓ framework

advanced

Choosing the Correct Docker Compose Service for Selenium Grid Hub

In a Docker Compose file for Selenium Grid, which service configuration correctly defines the hub to expose port 4444 and allow nodes to connect?

Selenium Java

services:
  selenium-hub:
    image: selenium/hub:4.10.0-20230628
    ports:
      - "4444:4444"
    environment:
      - GRID_MAX_SESSION=5
      - GRID_BROWSER_TIMEOUT=60
    # What else is needed here?

A Add 'network_mode: bridge' to allow communication with nodes on the same network.

B Add 'expose: 5555' to open the node port on the hub service.

C Add 'depends_on: [selenium-node-chrome]' to start nodes before the hub.

D Add 'restart: always' to ensure the hub restarts on failure.

💡 Hint

Nodes and hub must be on the same Docker network to communicate.

Setting 'network_mode: bridge' or defining a shared network allows containers to communicate internally.

🧠 Conceptual

expert

Understanding Session Distribution in Docker Selenium Grid

In a Selenium Grid setup with multiple Docker nodes, how does the hub decide which node to assign a new test session?

A The hub assigns sessions based on node availability and browser capabilities matching the test request.

B The hub assigns sessions randomly to any node regardless of browser type or load.

C The hub always assigns sessions to the newest node started in Docker.

D The hub assigns sessions only to nodes running on the same physical machine.

💡 Hint

Think about how the hub matches test requirements to node capabilities.

The hub matches requested browser and platform capabilities with nodes that have free slots and the required browsers.