This project is a mini container runtime built from scratch. It teached me how containers work under the hood using linux syscalls like: clone,unshare, mount,chroot,etc; along with new knowledge about memory management in zig.
This is a step-by-step on how to get the container up and running to test it and see its limitations:
0º If you don't already have it, download docker and make sure it's working by running docker run hello
1º Clone the repository git clone https://github.com/DaVinceDev/container-test
NOTE: DO NOT! AND I REPEAT DO NOT RUN THIS OUTSIDE THE DOCKER CONTAINER, WHATEVER HAPPENS IT'S YOUR FAULT.
2º Go to the repo directory and create a docker container using the Dockerfile
cd container-test/
docker build -t <container_name> .
3º Run the container with the necessary permissions, the code will not run if it doesn't
docker run --cap-add=SYS_ADMIN --cap-add=SYS_CHROOT --cap-add=SYS_PTRACE -it <containername>
4º Build the executable for the container, running the code directly fails when it comes to fetching for PID's
zig build-exe container.zig
5º Run the executable and pass an argument like bash. The best argument for the test anyways lol
./container bash
There! You're inside a container.
Now that you're inside the container, you might want to test atleast two things:
Hostname test
and
Fetch for PID's
Inside the container(assuming you passed bash as argument) type the hostname command and it'll echo the container hostname. To change it you just go
hostname zig-box or whatever you want to call it. Then again try hostname and it'll echo the name you gave it. Now exit the container and try hostname
and it should echo the development container ID.
Again, assuming you're inside the container (not the dev one) if you try to type ps it will fail because it's not installed. But then you might notice you're
inside a ubuntu container(development one) so it should have ps command. Happens that the rootfs(root filesystem) does not have ps by default in the test
container. But you can install it with:
apt-get update to update the database
apt-get procps to install ps
And then you can try again ps and should show: the container, bash and ps. And you now it's working if the TTY's are unknow.
You can check the code and the notes to see and understand the process behind it.
This code is an adaptation in zig of this video:
Containers from scratch in Go: https://youtu.be/Utf-A4rODH8?si=jzC6Zg0cWRUceNRD
This Liz Rice did an amazing job at simplifying the process of creation of a container and it would be my bad if I didn't mention her and the reference of this project