youki: A container runtime in Rust

youki is an implementation of runtime-spec in Rust, referring to runc.

About the name

youki is pronounced as /joʊki/ or yoh-key. youki is named after a Japanese word 'youki', which means 'a container'. In Japanese language, youki also means 'cheerful', 'merry', or 'hilarious'.

Motivation

Here is why I am rewriting a new container runtime in Rust.

• Rust is one of the best languages to implement oci-runtime. Many container tools are written in Go. It's all very nice products. However, the container runtime requires the use of system calls, which requires a bit of special handling when implemented in Go. This is too tricky(e.g. namespaces(7), fork(2)); with Rust, it's not that tricky and you can use system calls. Also, unlike C, Rust provides the benefit of memory management. Rust is not yet a major player in the container field, and Rust has the potential to contribute more to this field. I hope to be one of the examples of how Rust can be used in this field.
• youki has the potential to be faster and use less memory than runc. This means that it can work in environments with tight memory usage. I don't have any benchmarks, etc., as it is not yet fully operational, but I expect that it will probably perform better when implemented in Rust. In fact, crun, a container runtime implemented in C, is quite high performance. For example, it may be possible to experiment with asynchronous processing using async/await in some parts.
• The development of railcar has been suspended. This project was very nice but is no longer being developed. This project is inspired by it.
• I have fun implementing this. In fact, this may be the most important.

Related project

• containers/oci-spec-rs - OCI Runtime and Image Spec in Rust

Status of youki

youki is not at the practical stage yet. However, it is getting closer to practical use, running with docker and passing all the default tests provided by opencontainers/runtime-tools.

Feature	Description	State
Docker	Running via Docker	✅
Podman	Running via Podman	It works, but cgroups isn't supported. WIP on #24
pivot_root	Change the root directory	✅
Mounts	Mount files and directories to container	✅
Namespaces	Isolation of various resources	✅
Capabilities	Limiting root privileges	✅
Cgroups v1	Resource limitations, etc	✅
Cgroups v2	Improved version of v1	Support is complete except for devices. WIP on #78
Seccomp	Filtering system calls	WIP on #25
Hooks	Add custom processing during container creation	✅
Rootless	Running a container without root privileges	It works, but cgroups isn't supported. WIP on #77
OCI Compliance	Compliance with OCI Runtime Spec	47 out of 55 test cases passing

Design and implementation of youki

More details are in the works #14

Getting Started

Local build is only supported on linux. For other platforms, please use Vagrantfile that we prepared.

Requires

• Rust(See here)
• Docker(See here)

Dependencies

Debian, Ubuntu and related distributions

$ sudo apt-get install   \
      pkg-config         \
      libsystemd-dev     \
      libdbus-glib-1-dev \
      build-essential    \
      libelf-dev

Fedora, Centos, RHEL and related distributions

$ sudo dnf install   \
      pkg-config     \
      systemd-devel  \
      dbus-devel     \
      elfutils-libelf-devel \

Build

$ git clone git@github.com:containers/youki.git
$ cd youki
$ ./build.sh
$ ./youki -h # you can get information about youki command

Tutorial

Let's try to run a container that executes sleep 30 with youki. This tutorial may need root permission.

$ git clone git@github.com:containers/youki.git
$ cd youki
$ ./build.sh

$ mkdir -p tutorial/rootfs
$ cd tutorial
# use docker to export busybox into the rootfs directory
$ docker export $(docker create busybox) | tar -C rootfs -xvf -

Then, we need to prepare a configuration file. This file contains metadata and specs for a container, such as the process to run, environment variables to inject, sandboxing features to use, etc.

$ ../youki spec  # will generate a spec file named config.json

We can edit the config.json to add customized behaviors for container. Here, we modify the process field to run sleep 30.

  "process": {
    ...
    "args": [
      "sleep", "30"
    ],

  ...
  }

Then we can explore the lifecycle of a container:

$ cd ..                                                # go back to the repository root
$ sudo ./youki create -b tutorial tutorial_container   # create a container with name `tutorial_container`
$ sudo ./youki state tutorial_container                # you can see the state the container is `created`
$ sudo ./youki start tutorial_container                # start the container
$ sudo ./youki list                                    # will show the list of containers, the container is `running`
$ sudo ./youki delete tutorial_container               # delete the container

Change the command to be executed in config.json and try something other than sleep 30.

Usage

Starting the docker daemon.

$ dockerd --experimental --add-runtime="youki=$(pwd)/target/x86_64-unknown-linux-gnu/debug/youki"

In case you get an error like :

failed to start daemon: pid file found, ensure docker is not running or delete /var/run/docker.pid

That means your normal Docker daemon is running, and it needs to be stopped. For that, open a new shell in same directory and run :

$ systemctl stop docker # might need root permission

Now in the same shell run the first command, which should start the docker daemon.

You can use youki in a different terminal to start the container.

$ docker run -it --rm --runtime youki busybox

Afterwards, you can close the docker daemon process in other the other terminal. To restart normal docker daemon (if you had stopped it before), run :

$ systemctl start docker # might need root permission

Integration test

Go and node-tap are required to run integration test. See the opencontainers/runtime-tools README for details.

$ git submodule update --init --recursive
$ ./integration_test.sh
# run specific test_cases with pattern
$ ./integration_test.sh linux_*

Setting up Vagrant

You can try youki on platforms other than linux by using the Vagrantfile we have prepared.

$ git clone git@github.com:containers/youki.git
$ cd youki
$ vagrant up
$ vagrant ssh

# in virtual machine
$ cd youki
$ ./build.sh

Community

We also have an active Discord if you'd like to come and chat with us.

Contribution

This project welcomes your PR and issues. For example, refactoring, adding features, correcting English, etc. If you need any help, you can contact me on Twitter.

Thanks to all the people who already contributed!