What happens when you put your app in a Docker container

An app runs fine on your laptop. Then it crashes on the server. Docker is the usual fix for this problem. A container looks like a small computer in a box. On the server, it is just one more running program, next to all the others. Follow one web app into Docker, step by step: the Dockerfile and the image, the registry, docker run, namespaces, port publishing, image layers, volumes, cgroups, and how a container is different from a virtual machine.