linuxexpert-practice-labs/labs/linux-plus/2-6-1-runtimes-and-images

Linux+ 2.6.1: Container runtimes and images

Pulling and inspecting an image, building one from a Containerfile, rebuilding with the layer cache, and tagging and pruning, all rootless.

Before you start

The VM needs internet access to pull images. The lab installs Podman and creates user alice (password Lab-Pass-1), with lingering turned on so her user services run. Do every task as alice: log in as her, or use sudo -iu alice and then export XDG_RUNTIME_DIR=/run/user/$(id -u).

Tasks

1. Pull registry.access.redhat.com/ubi10/ubi-minimal, list your images, and show its OS, architecture and default command.
2. In ~/img, write app.py (it prints hello from and its arguments) and a Containerfile based on that image that installs python3 with microdnf, copies app.py to /opt/app.py, runs as user 1001, has the entrypoint python3 /opt/app.py and the default argument default. Build it as hello:1.0, run it with and without arguments, and look at its history.
3. Change app.py, rebuild hello:1.0, and notice that the package layer comes from the cache.
4. Tag hello:1.0 as hello:latest, remove the latest tag again, and prune the dangling images that rebuilding left behind.

Hints

• podman pull, podman images, podman image inspect --format '{{.Os}}/{{.Architecture}} {{.Config.Cmd}}'.
• FROM, RUN microdnf install -y python3 && microdnf clean all, COPY, USER 1001, ENTRYPOINT ["python3", "/opt/app.py"], CMD ["default"]; podman build -t hello:1.0 ., podman run --rm, podman history.
• "Using cache" in the build output.
• podman tag, podman rmi, podman image prune -f, podman images -f dangling=true.