I like to think about images and containers by analogy. When you `docker run` an image, it starts up inside a container runtime. A container image also has some descriptive data, such as the start-up command, the ports to expose, and volumes to mount. Those layers form an immutable filesystem. BackgroundĪ docker image is made up of layers. We will be using variations on this Dockerfile throughout this tutorial.īut what is happening when you call `docker build`? To understand that, we will need a little background. RUN echo "standard docker build" > /built.txt" Here is an example Dockerfile: FROM alpine The familiar base images Alpine, Ubuntu, and Debian are all created this way. 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. We can create container images in several ways.
We will create an image programmatically and then develop a trivial syntactic frontend and use it to build an image. 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. How are containers made? Usually, from a series of statements like `RUN`, `FROM`, and `COPY`, which are put into a Dockerfile and built. 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.
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