cri-o - OCI-based implementation of Kubernetes Container Runtime Interface

Status: pre-alpha

What is the scope of this project?

cri-o is meant to provide an integration path between OCI conformant runtimes and the kubelet. Specifically, it implements the Kubelet Container Runtime Interface (CRI) using OCI conformant runtimes. The scope of cri-o is tied to the scope of the CRI.

At a high level, we expect the scope of cri-o to be restricted to the following functionalities:

• Support multiple image formats including the existing Docker image format
• Support for multiple means to download images including trust & image verification
• Container image management (managing image layers, overlay filesystems, etc)
• Container process lifecycle management
• Monitoring and logging required to satisfy the CRI
• Resource isolation as required by the CRI

What is not in scope for this project?

• Building, signing and pushing images to various image storages
• A CLI utility for interacting with cri-o. Any CLIs built as part of this project are only meant for testing this project and there will be no guarantees on the backwards compatibility with it.

This is an implementation of the Kubernetes Container Runtime Interface (CRI) that will allow Kubernetes to directly launch and manage Open Container Initiative (OCI) containers.

The plan is to use OCI projects and best of breed libraries for different aspects:

• Runtime: runc (or any OCI runtime-spec implementation) and oci runtime tools
• Images: Image management using containers/image
• Storage: Storage and management of image layers using containers/storage
• Networking: Networking support through use of CNI

It is currently in active development in the Kubernetes community through the design proposal. Questions and issues should be raised in the Kubernetes sig-node Slack channel.

Getting started

Prerequisites

runc version 1.0.0.rc1 or greater is expected to be installed on the system. It is picked up as the default runtime by ocid.

Build Dependencies

Required

Fedora, CentOS, RHEL, and related distributions:

yum install -y \
  runc \
  btrfs-progs-devel \
  device-mapper-devel \
  glib2-devel \
  glibc-devel \
  gpgme-devel \
  libassuan-devel \
  libgpg-error-devel

Debian, Ubuntu, and related distributions:

apt install -y \
  runc \
  btrfs-tools \
  libassuan-dev \
  libdevmapper-dev \
  libglib2.0-dev \
  libc6-dev \
  libgpgme11-dev \
  libgpg-error-dev

If using an older release or a long-term support release, be careful to double-check that the version of runc is new enough, or else build your own.

Optional

Fedora, CentOS, RHEL, and related distributions:

yum install -y \
  libseccomp-devel \
  libapparmor

Debian, Ubuntu, and related distributions:

apt install -y \
  libseccomp-dev \
  libapparmor-dev

Build

git clone https://github.com/kubernetes-incubator/cri-o # or your fork
cd cri-o
make install.tools
make
sudo make install

To avoid building cri-o with seccomp support, add BUILDTAGS="" when running make instead:

make BUILDTAGS=""
sudo make install

Build Tags

cri-o supports optional build tags for compiling support of various features. To add build tags to the make option the BUILDTAGS variable must be set.

make BUILDTAGS='seccomp apparmor'

Build Tag	Feature	Dependency
seccomp	syscall filtering	libseccomp
selinux	selinux process and mount labeling
apparmor	apparmor profile support	libapparmor

Running pods and containers

Follow this tutorial to get started with CRI-O.

Setup CNI networking

Follow the steps below in order to setup networking in your pods using the CNI bridge plugin. Nothing else is required after this since CRI-O automatically setup networking if it finds any CNI plugin.

$ go get -d github.com/containernetworking/cni
$ cd $GOPATH/src/github.com/containernetworking/cni
$ sudo mkdir -p /etc/cni/net.d
$ sudo sh -c 'cat >/etc/cni/net.d/10-mynet.conf <<-EOF
{
    "cniVersion": "0.2.0",
    "name": "mynet",
    "type": "bridge",
    "bridge": "cni0",
    "isGateway": true,
    "ipMasq": true,
    "ipam": {
        "type": "host-local",
        "subnet": "10.88.0.0/16",
        "routes": [
            { "dst": "0.0.0.0/0"  }
        ]
    }
}
EOF'
$ sudo sh -c 'cat >/etc/cni/net.d/99-loopback.conf <<-EOF
{
    "cniVersion": "0.2.0",
    "type": "loopback"
}
EOF'
$ ./build
$ sudo mkdir -p /opt/cni/bin
$ sudo cp bin/* /opt/cni/bin/

Current Roadmap

1. Basic pod/container lifecycle, basic image pull (already works)
2. Support for tty handling and state management
3. Basic integration with kubelet once client side changes are ready
4. Support for log management, networking integration using CNI, pluggable image/storage management
5. Support for exec/attach
6. Target fully automated kubernetes testing without failures