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Compiling Containers – Dockerfiles, LLVM and BuildKit

Today we’re featuring a blog from Adam Gordon Bell at Earthly who writes about how BuildKit, a technology developed by Docker and the community, works and how to write a simple frontend. Earthly uses BuildKit in their product.

Introduction

How are containers made? Usually, from a series of statements like `RUN`, `FROM`, and `COPY`, which are put into a Dockerfile and built.  But how are those commands turned into a container image and then a running container?  We can build up an intuition for how this works by understanding the phases involved and creating a container image ourselves. We will create an image programmatically and then develop a trivial syntactic frontend and use it to build an image.

On `docker build`

We can create container images in several ways. We can use Buildpacks, we can use build tools like Bazel or sbt, but by far, the most common way images are built is using `docker build` with a Dockerfile.  The familiar base images Alpine, Ubuntu, and Debian are all created this way.     

Here is an example Dockerfile:

FROM alpine
COPY README.md README.md
RUN echo "standard docker build" > /built.txt"

We will be using Continue reading