Docker is a free and open source containerization platform that allows you to package up an application or service with all of its dependencies into a standardized image. It allows us to build and replicate images on any host, removing the inconsistencies of dev environments and reducing onboarding timelines considerably. The Docker image contains the code, runtime, system libraries and anything that required to deploy an application. If you are developing a Ruby application, you will need a specific version of Ruby, Bundler, project-specific gems and other dependencies based on the operating system. In this case, you can use Docker to keep things organized. Docker simplifies your workflow and the process of deploying your application to production.