Explain Multi-stage builds

Multi-stages builds allow you to produce smaller container images by splitting the build process into multiple stages.

As an example, imagine you have one Containerfile/Dockerfile where you first build the application and then run it. The whole build process of the application might be using packages and libraries you don't really need for running the application later. Moreover, the build process might produce different artifacts which not all are needed for running the application.

How do you deal with that? Sure, one option is to add more instructions to remove all the unnecessary stuff but, there are a couple of issues with this approach:

1. You need to know what to remove exactly and that might be not as straightforward as you think
2. You add new layers which are not really needed

A better solution might be to use multi-stage builds where one stage (the build process) is passing the relevant artifacts/outputs to the stage that runs the application.