CRI-O - OCI-based implementation of Kubernetes Container Runtime Interface

Compatibility matrix: CRI-O ⬄ Kubernetes

CRI-O and Kubernetes follow the same release cycle and deprecation policy. For more information visit the Kubernetes versioning documentation.

Version - Branch	Kubernetes branch/version	Maintenance status
CRI-O 1.12.x - release-1.12	Kubernetes 1.12 branch, v1.12.x	=
CRI-O 1.13.x - release-1.13	Kubernetes 1.13 branch, v1.13.x	=
CRI-O 1.14.x - release-1.14	Kubernetes 1.14 branch, v1.14.x	=
CRI-O 1.15.x - release-1.15	Kubernetes 1.15 branch, v1.15.x	=
CRI-O HEAD - master	Kubernetes master branch	✓

Key:

✓ Changes in main Kubernetes repo about CRI are actively implemented in CRI-O
= Maintenance is manual, only bugs will be patched.

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 backward 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.

Commands

Command	Description
crio(8)	OCI Kubernetes Container Runtime daemon

Note that kpod and its container management and debugging commands have moved to a separate repository, located here.

Configuration

File	Description
crio.conf(5)	CRI-O Configuration file
policy.json(5)	Signature Verification Policy File(s)
registries.conf(5)	Registries Configuration file
storage.conf(5)	Storage Configuration file

OCI Hooks Support

You can configure CRI-O to inject OCI Hooks when creating containers.

CRI-O Usage Transfer

Useful information for ops and dev transfer as it relates to infrastructure that utilizes CRI-O

Communication

For async communication and long running discussions please use issues and pull requests on the github repo. This will be the best place to discuss design and implementation.

For chat communication we have an IRC channel #CRI-O on chat.freenode.net, and a channel on the Kubernetes slack that everyone is welcome to join and chat about development.

Awesome CRI-O

We maintain a curated list of links related to CRI-O. Did you find something interesting on the web about the project? Awesome, feel free to open up a PR and add it to the list.

Getting started

Installing CRI-O

To install CRI-O, you can use your distributions package manager:

Fedora 30 and later: sudo dnf module install cri-o Fedora 29, CentOS, RHEL, and related distributions: sudo yum install crio openSUSE: sudo zypper install cri-o

On Ubuntu distributions, there is a dedicated PPA provided by Project Atomic:

sudo apt-add-repository ppa:projectatomic/ppa
sudo apt-get update -qq
sudo apt-get install cri-o-[REQUIRED VERSION]

Alternatively, if you'd rather build CRI-O from source, checkout our setup guide. We also provide a way in building static binaries of CRI-O via nix.

Running CRI-O

You can run a local version of Kubernetes with CRI-O using local-up-cluster.sh:

Clone the Kubernetes repository
From the Kubernetes project directory, run:

CGROUP_DRIVER=systemd \
CONTAINER_RUNTIME=remote \
CONTAINER_RUNTIME_ENDPOINT='unix:///var/run/crio/crio.sock' \
./hack/local-up-cluster.sh

For more guidance in running CRI-O, visit our tutorial page

The HTTP status API

CRI-O exposes per default the gRPC API to fulfill the Container Runtime Interface (CRI) of Kubernetes. Besides this, there exists an additional HTTP API to retrieve further runtime status information about CRI-O. Please be aware that this API is not considered to be stable and production use-cases should not rely on it.

On a running CRI-O instance, we can access the API via an HTTP transfer tool like curl:

$ sudo curl -v --unix-socket /var/run/crio/crio.sock http://localhost/info | jq
{
  "storage_driver": "btrfs",
  "storage_root": "/var/lib/containers/storage",
  "cgroup_driver": "cgroupfs",
  "default_id_mappings": { ... }
}

The following API entry points are currently supported:

Path	Content-Type	Description
`/info`	`application/json`	General information about the runtime, like `storage_driver` and `storage_root`.
`/containers/:id`	`application/json`	Dedicated container information, like `name`, `pid` and `image`.
`/config`	`application/toml`	The complete TOML configuration (defaults to `/etc/crio/crio.conf`) used by CRI-O.

The tool crio-status can be used to access the API with a dedicated command line tool. It supports all API endpoints via the dedicated subcommands config, info and containers, for example:

$ sudo go run cmd/crio-status/main.go info
cgroup driver: cgroupfs
storage driver: btrfs
storage root: /var/lib/containers/storage
default GID mappings (format <container>:<host>:<size>):
  0:0:4294967295
default UID mappings (format <container>:<host>:<size>):
  0:0:4294967295

Weekly Meeting

A weekly meeting is held to discuss CRI-O development. It is open to everyone. The details to join the meeting are on the wiki.

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