As a base image, I am using node image that runs under Alpine Linux, a lightweight Linux distribution. I want to expose two ports. EXPOSE is not publishing any ports, it is just a form of a documentation. It is possible to specify ports with Docker Compose later. Port 3000 is the port we use to run our web server, and 9229 is a default port for Node.js Inspector. After we coping package.json and package-lock.json we install dependencies. Coping the rest of files happens later to maximize benefits of docker caching intermediate containers.