# Running in Docker and Grid

> Moving the browser off the machine that runs the tests, with Selenium Grid and the project's Docker images, so a suite can run in parallel and against several browsers.

URL: https://deploy-preview-2974--selenium-dev.netlify.app/documentation/guides/docker_and_grid/
Site index: https://deploy-preview-2974--selenium-dev.netlify.app/llms.txt

---

A suite that takes an hour because every test starts its own browser on the same machine.
A requirement to test on a browser that is not installed where the tests run. A build server
that must not have a browser on it at all. In each case the browser needs to be somewhere
other than the test process.

## Recommended approach

Selenium Grid is a server that accepts WebDriver sessions over HTTP and routes them to
browsers it manages. Your test code changes in exactly one place: instead of constructing a
local driver, construct a remote one with the Grid URL and the browser options. Everything
else stays the same, so a suite can run locally during development and on a Grid in CI with a
single configuration switch.

**Standalone** mode runs the whole Grid in one process and is the right starting point. It
needs a Java runtime and the Selenium Server jar, listens on `http://localhost:4444`, and can
use Selenium Manager to fetch drivers for the browsers it finds. **Hub and Node** spreads
browsers across several machines, and **distributed** mode separates each Grid component for
large installations.

The quickest way to get a Grid, and the only way to get one with no browser on the host, is
the project's own Docker images in the
[docker-selenium](https://github.com/SeleniumHQ/docker-selenium) repository. They package the
Grid, a browser and its driver, and are published for each Selenium release. A single
`docker run` gives you a standalone Grid with Chrome, Firefox or Edge; the repository also has
Docker Compose and Kubernetes examples, video recording, and VNC for watching a session.

When the browser is remote, files to upload must reach the node first, through a file
detector, and downloads must be enabled on the Grid and fetched back through the client. Both
are covered on the remote WebDriver page.

Point a test at a Grid:

**Java**

```java
ChromeOptions options = getDefaultChromeOptions();
driver = new RemoteWebDriver(gridUrl, options);
```

**Python**

```python
options = get_default_chrome_options()
driver = webdriver.Remote(command_executor=grid_url, options=options)
```

**CSharp**

```csharp
var options = new ChromeOptions();
driver = new RemoteWebDriver(GridUrl, options);
```

**Ruby**

```ruby
options = Selenium::WebDriver::Options.chrome
driver = Selenium::WebDriver.for :remote, url: grid_url, options: options
```

**JavaScript**

```javascript
const options = new Chrome.Options().addArguments('--no-sandbox')
driver = new Builder().forBrowser(Browser.CHROME).setChromeOptions(options).usingServer(gridUrl).build()
```

## Common errors

* [SessionNotCreatedException](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/webdriver/troubleshooting/errors/index.md#sessionnotcreatedexception):
  no node on the Grid can satisfy the requested browser and version. Check the Grid's status
  page at the Grid URL for the capabilities it offers.
* [InvalidArgumentException](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/webdriver/troubleshooting/errors/index.md#invalidargumentexception):
  a local file path was sent to a remote browser. Set a file detector so the file is uploaded.
* [WebDriverException](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/webdriver/troubleshooting/errors/index.md#webdriverexception)
  with a connection error: the Grid URL is wrong, the server is not running, or a firewall is
  between the client and the Grid.

## Reference

* [Grid getting started](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/grid/getting_started/index.md): standalone, hub and node, distributed
* [Grid configuration](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/grid/configuration/index.md) and
  [advanced features](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/grid/advanced_features/index.md)
* [Remote WebDriver](https://deploy-preview-2974--selenium-dev.netlify.app/documentation/webdriver/drivers/remote_webdriver/index.md): file uploads and downloads with a Grid
* [docker-selenium](https://github.com/SeleniumHQ/docker-selenium): the project's Docker images and deployment examples