rustainer

A container implementation using User Namespaces, CGroups, and slirp4netns in Rust.

Implementation Status

• User Namespaces
• Networking (with slirp4netns)
  • Outgoing Connections
  • Port Forwarding to expose container
• CGroups (needs integration for delegation mechanisms)
• Clear Environment Variables
• Handling setgroups() inside the container
• Proper PTY handling (use tmux inside the container for now)
• Ability to fetch images from Docker Registry
• Image storage
• Handling whiteout files in layers

Dependencies

• slirp4netns
• new{uid,gid}map: Likely provided by the shadow or uidmap package, depending on distribution

Usage

cargo run -- <image_name> <tag>

Example:

cargo run -- alpine latest

This fetches the Alpine Linux image, sets up the container environment, and drops you into a shell inside the container.

Inside the Container

Once inside the container, you can verify the isolation:

/ # whoami
root
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
...
4: tap0: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether fe:7c:24:98:65:d3 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.100/24 brd 10.0.2.255 scope global tap0
       valid_lft forever preferred_lft forever
...

You can install packages and access the internet:

/ # apk add curl
...
/ # curl https://httpbin.org/get
{
  "args": {}, 
  "headers": {
    "Accept": "*/*", 
    "Host": "httpbin.org", 
    "User-Agent": "curl/8.3.0", 
  }, 
  "origin": "XX.XXX.XXX.XX",
  "url": "https://httpbin.org/get"
}

Project Goals

This project aims to provide a lightweight containerization solution with a focus on security and efficiency. It's been a great way to deepen my understanding of container technologies and Linux systems programming.

Future Work

• Improve CGroup integration
• Enhance PTY handling
• Implement handling of whiteout files in layers

Contributions and feedback are welcome!