This guide details the steps to deploy a Selenium Grid using Docker containers. The setup involves creating a network, launching a Hub, and connecting multiple browser Nodes.

Prerequisites

• A cloud server (Ubuntu used in this example) with Docker installed.
• Access to the official Selenium Docker images on Docker Hub.

Core Setup Process

1. Create a Docker Network

First, establish a dedicated Docker network too allow the Hub and Node containers to communicate.

docker network create selenium-grid-network

2. Start the Seleniumm Hub Container

Launch the Hub container, mapping its internal ports to the host and attaching it to the created network.

docker run -d -p 4442-4444:4442-4444 \
  --net selenium-grid-network \
  --name selenium-hub \
  selenium/hub:latest

3. Start Browser Node Containers

Start Node containers for different browsers (Chrome, Firefox, Edge). They connect to the Hub via the shared network and environment variables.

For Linux/macOS (Bash):

docker run -d --net selenium-grid-network \
  -e SE_EVENT_BUS_HOST=selenium-hub \
  --shm-size="2g" \
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
  selenium/node-chrome:latest

docker run -d --net selenium-grid-network \
  -e SE_EVENT_BUS_HOST=selenium-hub \
  --shm-size="2g" \
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
  selenium/node-firefox:latest

docker run -d --net selenium-grid-network \
  -e SE_EVENT_BUS_HOST=selenium-hub \
  --shm-size="2g" \
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
  selenium/node-edge:latest

For Windows (PowerShell):

docker run -d --net selenium-grid-network `
  -e SE_EVENT_BUS_HOST=selenium-hub `
  --shm-size="2g" `
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 `
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 `
  selenium/node-chrome:latest

docker run -d --net selenium-grid-network `
  -e SE_EVENT_BUS_HOST=selenium-hub `
  --shm-size="2g" `
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 `
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 `
  selenium/node-firefox:latest

docker run -d --net selenium-grid-network `
  -e SE_EVENT_BUS_HOST=selenium-hub `
  --shm-size="2g" `
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 `
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 `
  selenium/node-edge:latest

4. Connect Your Tests

Configure your WebDriver tests to connect to the Grid at http://<your-server-ip>:4444.

5. Verify the Grid (Optional)

You can view the Grid status and connected Nodes via the web UI at http://<your-server-ip>:4444/ui.

Advanced Configuration and Notes

Image Tagging Convention

While latest is used for simplicity, it's recommended to pin specific versions for stability. The official tagging convention is: selenium/hub-<Major>.<Minor>.<Patch>-<YYYYMMDD>

For example, Selenium Grid Server 4.9.0 released on April 26, 2023, would have tags like 4, 4.9, 4.9.0, and 4.9.0-20230426.

Custom Node Configuration Example

This example shows a more customized Chrome Node setup, including session limits, port mapping for VNC, and shared memory optimization.

docker run -d --net selenium-grid-network \
  --name chrome-node-01 \
  -p 5902:5900 \
  -e SE_EVENT_BUS_HOST=selenium-hub \
  -e SE_NODE_MAX_SESSIONS=20 \
  -e NODE_MAX_INSTANCES=20 \
  -e SE_NODE_OVERRIDE_MAX_SESSIONS=true \
  -e SE_EVENT_BUS_PUBLISH_PORT=4442 \
  -e SE_EVENT_BUS_SUBSCRIBE_PORT=4443 \
  -v /dev/shm:/dev/shm \
  selenium/node-chrome:latest

Key Parameters Explained:

• --name: Assigns a custom name to the container.
• -p 5902:5900: Maps the container's VNC server port (5900) to the host port 5902, allowing remote desktop viewing.
• -e SE_NODE_MAX_SESSIONS=20: Limits the maximum number of concurrent browser sessions on this Node to 20.
• -e NODE_MAX_INSTANCES=20: Defines the maximum number of browser instances that can run in parallel. Typically matches SE_NODE_MAX_SESSIONS.
• -v /dev/shm:/dev/shm: Mounts the host's sharedd memory to the container, which can improve performance for browsers like Chrome.
• Ports 4442-4443 are used for internal communication between the Hub and Nodes.
• Port 4444 is the main entry point for WebDriver clients and hosts the Grid UI.

Installing VNC Viewer for Remote Monitoring

To visually monitor browser sessions on a Node:

1. Download and install VNC Viewer from the official website.
2. Create a new connection.
3. Enter the server's IP address and the mapped VNC port (e.g., 5902 from the example above).
4. Connect using the default password: secret.

Cleanup

When finished, you can stop the containers and remove the Docker network.

docker network rm selenium-grid-network

For comprehensive documentation and more advanced configurasions, refer to the official Docker-Selenium GitHub repository.