Containerization has revolutionized the way software is developed, tested, and deployed. While Docker has been a popular choice for containerization, Podman has emerged as a viable alternative, especially for users who prefer a rootless, daemonless, and more secure container experience. In this blog post, we will explore how to build Debian-based container images using Podman while integrating systemd inside them. This allows you to run services and manage them using systemd, just like you would on a traditional server.
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Why Would You Do That?
Most system administrators use automation and/or infrastructure as code tools for managing their environments. As the infra becomes more complex, they need a fast and reliable way of testing the changes.
The integration of systemd with containers comes here very handy. You can run smoke tests of changes in them. These images are not for production containers, but they have a huge task in development and testing.
Why Containers Don’t Have An Init System?
Containers intentionally do not include an init system to keep them lightweight and focused on their primary purpose: running applications. Process management and initialization are typically handled through other means, including entry points, supervision tools, or by sharing the host’s init system when necessary.
Building Containers With Systemd
A Containerfile is similar to a Dockerfile. If you are familiar with Docker it will help you to build a fully functional Debian Bookworm container that has Systemd running inside.
FROM debian:bookworm
RUN apt-get update && apt-get install -y systemd
CMD [ "/lib/systemd/systemd" ]
The above code can be used to build a new image based on Debian Bookworm.
podman build -t tmolnar-debian-systemd:latest -f Composefile
STEP 1/3: FROM debian:bookworm
Resolved "debian" as an alias (/etc/containers/registries.conf.d/shortnames.conf)
Trying to pull docker.io/library/debian:bookworm...
...
COMMIT tmolnar-debian-systemd:latest
--> 04df5c8a873
Successfully tagged localhost/tmolnar-debian-systemd:latest
Let’s check if there is an init process with PID 1!
Start a container instance from the image and check it with podman top:
podman run -itd --name systemd-test 04df
8d2511db24a66b842d9036f1e93cd4b6e68211ec97eb6531c194e77936abc48b
podman ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
8d2511db24a6 localhost/tmolnar-debian-systemd:latest /lib/systemd/syst... 5 seconds ago Up 4 seconds ago systemd-test
podman top 8d25
USER PID PPID %CPU ELAPSED TTY TIME COMMAND
root 1 0 0.000 15.762981116s ? 0s /lib/systemd/systemd
root 15 1 0.000 14.763070902s ? 0s /lib/systemd/systemd-journald
messagebus 23 1 0.000 14.763128842s ? 0s /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
root 24 1 0.000 14.763183451s ? 0s /lib/systemd/systemd-logind
root 26 1 0.000 14.763239641s pts/0 0s /sbin/agetty -o -p -- \u --noclear --keep-baud - 115200,38400,9600 xterm
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