We know how complicated it is to have a stable grid, and how hard it is to maintain over time with enough capabilities to cover most browsers and platforms. Internally, we found that ~75% of our tests were executed in Firefox/Chrome, and the remaining were executed in Safari/IE. We decided to develop a tool where docker-selenium nodes are created, used and disposed on demand. For Safari/IE, we just forward the tests to Sauce Labs/BrowserStack. Zalenium is an OSS extension to scale up and down your local grid dynamically with Docker containers. It uses Docker-Selenium to run tests in Firefox/Chrome, and when a different browser is needed, tests get redirected to a cloud testing service. Result: our tests suites run faster since most of the tests run on local Firefox/Chrome nodes, and we use in a smarter way the cloud testing service we pay for. Diego Molina – Software Engineer in Test, Zalando SE Leo Gallucci – Software Engineer, Tools and Infrastructure, Zalando SE