Why multi-stage build?

• One of the most difficult things about building images is keeping the size of an image as small as possible.
• The multi-stage build is a new feature and it requires Docker 17.05 or higher on the daemon and client.

Before multi-stage build!

• Before multi-stage build, It was common to have one Dockerfile to use for development (which has everything needed to build your application), and a smaller one to use for production, which only contained your application and exactly what was needed to run it.

How Multi-stage Build Works

• With multi-stage builds, you use multiple FROM statements in your Dockerfile.
• Each FROM instruction can use a different base, and each of them begins a new stage of the build.
• We can selectively copy artifacts from one stage to another, leaving behind everything we don’t want in the final image.

A Simple Multi-Stage Dockerfile

In multi-stage build, we pick the tasks of building and running our applications into different stages. Here, we start with a large image that includes all of the necessary dependencies needed to compile the binary executable of our application. This can be termed as the builder stage.

We then took a lightweight image for our run stage which includes only what is needed to run a binary executable. i.e just having jre in our final stage is sufficient to run our application. This can be termed as the production stage.

#devops #docker #docker #docker-image