Contain-it : A Mock Containerization Tool

MVP Status : not ready

TODO : Implement Root-fs extraction

This is a simple mock containerization tool written in Go. It mimics the behavior of basic container operations like pulling an image, unpacking it, and running commands within a new namespace. This tool does not fully replicate Docker's functionality but provides a lightweight alternative for educational purposes.

Features

• Pull Docker images and save them as tar.gz archives.
• Unpack the archives and run commands within new namespaces.
• Use cgroups to limit resources.
• Chroot to the unpacked image root filesystem.

Usage

Commands

1. run: Run a command inside a new container.

   ./cnts run <image> <command>

   Example:

   ./cnts run ubuntu /bin/sh

2. child: This is an internal command used by run. It sets up the new namespaces and executes the command.

3. pull: Pull a Docker image and store it as a tar.gz archive.

   ./cnts pull <image>

   Example:

   ./cnts pull ubuntu

Pull Script

The pull script is a helper bash script to fetch Docker images, export their filesystem, and save it to the assets directory.

#!/bin/bash

set -e

defaultImage="hello-world"

image="${1:-$defaultImage}"
container=$(docker create "$image")

docker export "$container" -o "./assets/${image}.tar.gz" > /dev/null
docker rm "$container" > /dev/null

docker inspect -f '{{.Config.Cmd}}' "$image:latest" | tr -d '[]\n' > "./assets/${image}-cmd"

echo "Image content stored in assets/${image}.tar.gz"

Building and Running

1. Build the Go program:

   go build -o cnts

2. Make the pull script executable:

   chmod +x pull

3. Use the commands as described above.

Note: You need to run these commands as root:

root@device:~# ./cnts run <image> <command>
root@device:~# ./cnts pull <image>

Note

This tool is for educational purposes and is not intended for production use. It demonstrates basic containerization concepts like namespaces and cgroups without the complexity and features of full-fledged container runtimes like Docker.