Multi-stage builds with Docker

Multi-stage Docker builds helps reduce the size of Docker images. It is supported in Docker versions 17+.

Using multi-stage builds, we can ensure that only the application and its necessary components are shipped. Previously a lot of complicated manipulation with shell scripts was required to clean up the shippable image.

Below is an example with a ASP.NET.

The sample ASP.NET code. It can be found at https://github.com/dotnet/dotnet-docker/tree/master/samples

1 — Use aspnetcore-build as base image for the first stage. This stage is named as build-env

2 — Set working directory for all further instructions

3 and 4 — Copy all csproj files and restore all project dependencies

5 — Copy all the other files

6 — Start build and output it to out directory

7 — Use aspnetcore as base imagefor the second and final stage

8 — Set working directory for all further instructions

9 — Using the name of the first stage ( build-env) to reference it in this stage
and copy the build artifacts

10 — Run the application using the artifact

Build the image using current directory as build context

Listing images, notice the reduced image size