What is a Selenium Grid?

Selenium Grid is a smart proxy server that runs Selenium tests across multiple machines and browsers in parallel. A Hub receives test requests and distributes them to Nodes - remote machines that execute the tests in their installed browsers.

What is Selenium Grid vs WebDriver?

Selenium WebDriver automates a single browser on one machine. Selenium Grid extends WebDriver to distribute those commands across multiple remote machines and browsers in parallel. WebDriver drives one browser, Grid orchestrates many.

What are the components of Selenium Grid?

Selenium Grid 4 has six components: the Router, Distributor, Session Map, New Session Queue, Event Bus, and Nodes. In simpler deployments these are bundled together as a single Hub plus Nodes setup.

What is the difference between Selenium Grid 3 and Selenium Grid 4?

Grid 4 is a full redesign of Grid 3. Grid 4 uses a microservice architecture instead of a monolithic Hub, supports Docker and Kubernetes natively, adopts the W3C WebDriver standard, and includes observability via OpenTelemetry. Grid 3 reached end-of-life in 2023.

How do I set up Selenium Grid?

Download the Selenium Server JAR from selenium.dev, start the Hub, register Nodes, then point your WebDriver tests to http://localhost:4444. Verify the setup by opening the Grid console at http://localhost:4444/ui in your browser.

Can I run Selenium Grid with Docker?

Yes. Official Docker images are published for the Hub, browser Nodes (Chrome, Firefox, Edge), and standalone Grid. A single docker-compose file can spin up a complete Grid and is the foundation for Kubernetes deployments.

What is the difference between local Selenium Grid and cloud Selenium Grid?

A local Selenium Grid runs on machines you own and maintain - you handle updates, patches, and scaling. A cloud Selenium Grid is hosted by a vendor with on-demand access to pre-configured browsers, OSes, and real devices. Cloud grids remove maintenance overhead and scale instantly.

Why move from an in-house Selenium Grid to the cloud?

In-house Grids need constant maintenance: browser updates, node crashes, peak-hour scaling, and hardware refreshes. Cloud Grids offload all of this and give you broader browser coverage, instant scale during regression runs, and predictable cost tied to concurrency.

How do I migrate my Selenium tests to a cloud Selenium Grid?

Replace your local WebDriver with RemoteWebDriver pointing at the cloud Grid URL, add your credentials and access key as environment variables, and set the browser, OS, and version through Capabilities. Your test logic stays unchanged.

Is Selenium Grid free?

Yes, Selenium Grid is free and open-source under the Apache 2.0 license. What costs money is the infrastructure you run it on - machines, browsers, devices, and engineering time to maintain them. Cloud providers charge for managed infrastructure and browser coverage.

How many tests can you run in parallel on Selenium Grid?

On a cloud Selenium Grid, parallel session count depends on your subscription plan. TestMu AI supports plans from a few concurrent sessions to thousands, with no infrastructure to manage. You can scale concurrency on demand to match your pipeline without any hardware constraints.

What is the fastest way to integrate Selenium Grid with CI/CD?

Point your test framework at the Grid's RemoteWebDriver URL and trigger the test command from your CI job (GitHub Actions, GitLab CI, Jenkins, CircleCI). Store credentials as pipeline secrets and use vendor-provided plugins for the fastest path.

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