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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →For a quick local Grid or a small CI run, start Selenium in Standalone mode as one Docker service. If you need browser sessions launched in separate containers, configure a Grid Node to map browser capabilities to Docker images and give it access to the Docker daemon. For multiple machines, choose Hub and Node; use Distributed mode when you need to deploy Grid components separately. These are related but distinct uses of Docker, and they have different networking requirements.
Choose what Docker should run
“Selenium Grid with Docker” can mean running the Grid server in a container, or having Grid launch browser containers for test sessions. You can use the first without the second. Decide whether you need one machine or capacity across multiple machines before choosing a topology.
- Standalone: one process on one machine, with the default RemoteWebDriver endpoint
http://localhost:4444. Selenium describes it as the simplest option for local development, quick pre-push suites and straightforward CI. - Hub and Node: one Hub endpoint coordinates Nodes, which can run on different machines. Add or remove Nodes to change capacity.
- Distributed: run Grid components separately. It gives more control over deployment, at the cost of managing additional services and their network paths. Selenium’s guide says these components are ideally on different machines.
For most initial Docker setups, start with Standalone. Move to Hub and Node when a single machine cannot provide the browser capacity you need or you need to combine machines. Use Distributed when independent component deployment is a real operational requirement.
Start Grid in Docker
The Selenium Docker project publishes the supported images and links to its detailed README: SeleniumHQ/docker-selenium. Use that README for a Compose recipe and compatible image tags for the release you plan to deploy. The project landing page alone does not establish a current canonical Compose file or image-tag recommendation, so avoid copying an old example or treating latest as a production pin.
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For a minimal Standalone deployment, follow the current project README’s Standalone service instructions, publish the Grid HTTP port to the host, and pin the Grid image to a version you have checked. The default endpoint is http://localhost:4444 when accessed from the same host. If the test runner is another container, localhost refers to that runner, not the Grid container; use a hostname reachable on the shared Docker network.
Run browser sessions in Docker containers
When Grid should create a fresh browser container for a session, configure the Node with Docker image-to-capability mappings and connectivity to the Docker daemon. Selenium’s TOML documentation shows the structure, including a disabled automatic driver scan and a Node session limit:
[node]
detect-drivers = false
max-sessions = 2
[docker]
# Set this to an address reachable by the Grid Node.
url = "http://docker-host:2375"
configs = [
"browser-image:tag", "{2browserName2: 2chrome2}"
]This illustrates the configuration shape, not a recommended current browser image tag. Replace browser-image:tag with an image and tag supported by the Docker Selenium project and compatible with the Grid version you deploy. In the capability JSON, map the requested browser capability to the image that should serve it. The Node uses the mapping to select the browser container for a matching session request.
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The Docker configuration requires the daemon to be exposed through HTTP/TCP for this setup. Treat that endpoint as privileged infrastructure: make it reachable only from the Grid Node and protect it using network controls. Do not expose an unauthenticated Docker daemon publicly.
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Selenium’s command-line and TOML options include Docker host and URL, Docker API version, browser server startup timeout and graceful stop period. Options vary by Grid release. Check the running version’s available settings with java -jar selenium-server.jar --config-help or the relevant role’s --help rather than assuming a flag copied from another release still applies. See the Selenium Grid CLI options and TOML options.
Allow the required network traffic
Publishing port 4444 is not enough for every topology. Expose only the ports required between the components in your chosen deployment, and make sure hostnames advertised by containers resolve and are reachable from their peers.
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| Topology | Network paths to plan |
|---|---|
| Standalone | Client or test runner to Grid HTTP endpoint, default port 4444. |
| Hub and Node | Client to Hub over HTTP; Node to Hub over HTTP and Event Bus. The documented default Hub Event Bus ports are 4442 and 4443, and the Node port must also be reachable. |
| Distributed | Expose the ports required by the components actually deployed. Selenium’s getting-started guide lists separate defaults for Event Bus, Session Map, New Session Queue, Distributor, Router and Node; do not assume the Hub-and-Node port set alone covers this layout. |
Port defaults can be changed in configuration. Confirm the ports for your selected Grid version and topology in the Selenium Grid getting-started guide and CLI options. Restrict firewall and container-network access to the clients and peer components that need it.
Check Grid, then create a session
- Open the Grid UI at
http://<grid-host>:4444, or requesthttp://<grid-host>:4444/status. - Inspect the status response for registered Nodes, available slots and active sessions. A running HTTP endpoint does not by itself prove that a browser image can start successfully.
- Submit a RemoteWebDriver request with the browser capability you mapped. Confirm that the session is created and that the requested browser is the one returned by the Node.
The status endpoint provides health and availability information; consult Selenium’s Grid endpoints documentation for endpoint details.
Plan capacity from observed tests
Selenium offers 1 CPU and 1 GB of RAM per browser as a rule-of-thumb starting point, not a universal sizing guarantee. Actual demand depends on the site, browser, test behavior and concurrency. Measure your own workload before setting the Node session limit or adding Nodes.
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- Track queued sessions, occupied slots and session startup failures.
- Watch CPU and memory pressure on both the Grid host and the machines running browser containers.
- Increase concurrency gradually and compare completion time and failure rates with the prior level.
- For sustained demand, scale Nodes rather than relying on an arbitrarily high per-Node session limit.
Selenium’s guide emphasizes that there is no one-size-fits-all Grid size and recommends ongoing performance measurement.
Secure the Grid endpoint
Selenium warns: “Failure to protect your Grid could result in one or more of the following occurring:” Its documented risks include third parties reaching internal web applications and files, or running custom binaries. Do not publish an unauthenticated Grid endpoint to the public internet. Use firewall rules and private networking, and configure authentication where appropriate; authentication does not replace network restrictions. See Selenium’s security guidance and configuration options.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshooting common Docker Grid failures
Grid responds, but no Node appears
- Confirm that the Node can reach the Hub’s HTTP and Event Bus ports and that the Node port is reachable.
- For Docker-backed sessions, verify the Node can reach the configured Docker daemon address and that the daemon is exposed on the required HTTP/TCP interface.
- Check that the browser image exists and that the requested capabilities match a configured image mapping.
A Node registers, but session creation fails
- Check the requested browser name and other capabilities against the mapping’s capability JSON.
- Verify that the image tag is compatible with the Grid version and can be pulled by the Docker daemon.
- Review container logs and increase the browser startup timeout only if the observed startup time justifies it.
Clients cannot reach Grid or peer containers
- From a client in another container, use the Grid service hostname, not
localhost. - For Hub and Node or Distributed deployments, open the component ports required by the topology, not just 4444.
- Check that the hostname the component advertises is resolvable and reachable from its peers.
A copied configuration flag is rejected
Options differ between releases. Run java -jar selenium-server.jar --config-help or the relevant role-specific --help on the deployed version and adapt the configuration to that output.
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Or skip the browser setup
If your goal is to capture a website image or PDF rather than run interactive browser tests, ScreenshotNeo is a screenshot API and MCP server; it is not a Selenium Grid replacement. One GET request can return a PNG, JPEG, WebP or PDF. The call below uses the documented API; see the ScreenshotNeo API docs for options.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpScreenshotNeo accepts cookie and consent banners before capture and removes more than 60 known consent platforms, newsletter popups and chat widgets; each step can be turned off. Bot checks, blank pages, timeouts, failed loads and cache hits are not billed, with response headers identifying the page verdict and billing status. Its MCP server provides take_screenshot, get_page_info and capture_pdf for AI agents. The Free plan includes 1,000 screenshots a month without a card; paid plans start at $5 for 3,000 shots.
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Frequently Asked Questions
Can Selenium Grid run browser tests in parallel?
Yes. Grid can allocate sessions to available Node slots; practical parallel capacity depends on measured browser and host resource use.
Can I run the test client in a Docker container too?
Yes. Put the client and Grid on a network where the client can resolve and reach the Grid service hostname; do not use localhost to refer to a different container.
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