docker-playground

📚 Learning and exploring Docker https://www.docker.com/.

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Standalone subprojects

This repository illustrates different concepts, patterns and examples via standalone subprojects. Each subproject is completely independent of the others and do not depend on the root project. This standalone subproject constraint forces the subprojects to be complete and maximizes the reader's chances of successfully running, understanding, and re-using the code.

The subprojects include:

basic/

A basic "hello world" example of Docker that starts a container, executes a command inside of it, then stops it.

See the README in basic/.

compose/

A simple Docker Compose example.

See the README in compose/.

dockerfile/

An example project that builds a simple Docker image using a Dockerfile.

See the README in dockerfile/.

introspective/

A Docker image that introspects Docker metadata and networking information about its environment.

See the README in introspective/.

registry/

This subproject illustrates how to run and use a local Docker registry.

See the README in registry/.

Wish List

General clean-ups, TODOs and things I wish to implement for this project:

• DONE Add Docker Compose examples
• Add non-Docker examples. (I hardly know anything about non-Docker container technology)
• SKIP Add an example showing a "depends-on" relationship using a shell script instead of Docker Compose (because Docker Compose doesn't support the "depends_on" property since a long time). UPDATE: depends_on is supported still, it just doesn't do what you might think. It doesn't wait for an "is ready" check. Docker calls this fact out in the docs and describes strategies for controlling start up order. Spoiler alert: it's not slick, it requires custom shell scripting which of course may not be palatable if you wanted to used Docker images off- the-shelf without having to make changes.
• DONE Create a CI build in GitHub Actions
• DONE Add a Dockerfile example
• DONE Consider doing a registry subproject. Docker supports this with an open source registry, very cool. UPDATE: yes I definitely want to do this because the registry exposes an HTTP API that formally (and completely?) implements the access to content-addressable entities (layers, manifests, configs). This HTTP API should be legible, unlike the sometimes opaque and varied behavior of the docker CLI for commands like inspect (in my opinion). The registry is especially authoritative because it implements OCI Distribution Specification. I'm not seeing the image layer get re-used as I expect in the dockerfile example. Maybe it's something to do with BuildKit and not using the cache, but I'm not sure. I want to actually illustrate layer re-use. I think if I use a local registry, maybe I can force this, or at least debug it. Interestingly though the file diff SHA digest is the same (good).

Reference

• Docker docs: Glossary