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Purpose

This repository contains the definitions for the Container Runtime Interface (CRI). CRI is a plugin interface which enables kubelet to use a wide variety of container runtimes, without the need to recompile. CRI consists of a protocol buffers and gRPC API. Read more about CRI API at kubernetes docs.

The repository kubernetes/cri-api is a mirror of https://github.com/kubernetes/kubernetes/tree/master/staging/src/k8s.io/cri-api. Please do not file issues or submit PRs against the kubernetes/cri-api repository as it is readonly, all development is done in kubernetes/kubernetes.

The CRI API is defined in kubernetes/kubernetes repository and is only intended to be used for kubelet to container runtime interactions, or for node-level troubleshooting using a tool such as crictl. It is not a common purpose container runtime API for general use, and is intended to be Kubernetes-centric. We try to avoid it, but there may be logic within a container runtime that optimizes for the order or specific parameters of call(s) that the kubelet makes.

Version skew policy

On a single Node there may be installed multiple components implementing different versions of CRI API.

For example, on a single node there might be:

  • Kubelet may call into Container Runtime (e.g. containerd) and Image Service Proxy (e.g. stargz-snapshotter). Container Runtime may be versioned with the OS Image, Kubelet is installed by system administrator and Image Service proxy is versioned by the third party vendor.
  • Image Service Proxy calls into Container Runtime.
  • CRI tools (e.g. crictl) may be installed by end user to troubleshoot, same as a third party daemonsets. All of them are used to call into the Container Runtime to collect container information.

So on a single node it may happen that Container Runtime is serving a newer version'd kubelet and older versioned crictl. This is a supported scenario within the version skew policy.

Version Skew Policy for CRI API

CRI API has two versions:

  • Major semantic version (known versions are v1alpha2 (removed in 1.26), v1).
  • Kubernetes version (for example: @1.23). Note, the cri-api Golang library is versioned as 0.23 as it doesn't guarantee Go types backward compatibility.

Major semantic version (e.g. v1) is used to introduce breaking changes and major new features that are incompatible with the current API.

Kubernetes version is used to indicate a specific feature set implemented on top of the major semantic version. All changes made without the change of a major semantic version API must be backward and forward compatible.

  • Kubelet must work with the older Container Runtime if it implements the same semantic version of CRI API (e.g. v1) of up to three Kubernetes minor versions back. New features implemented in CRI API must be gracefully degraded. For example, Kubelet of version 1.26 must work with Container Runtime implementing k8s.io/[email protected]+.
  • Kubelet must work with Container Runtime if it implements the same semantic version of CRI API (e.g. v1) of up to three minor versions up. New features implemented in CRI API must not change behavior of old method calls and response values. For example, Kubelet of version 1.22 must work with Container Runtime implementing k8s.io/[email protected].

Versioning

This library contains go classes generated from the CRI API protocol buffers and gRPC API.

The library versioned as 0.XX as Kubernetes doesn't provide any guarantees on backward compatibility of Go wrappers between versions. However CRI API itself (protocol buffers and gRPC API) is marked as stable v1 version and it is backward compatible between versions.

Versions like v0.<minor>.<patch> (e.g. v0.25.5) are considered stable. It is discouraged to introduce CRI API changes in patch releases and recommended to use versions like v0.<minor>.0.

All alpha and beta versions (e.g. k8s.io/[email protected]) should be backward and forward compatible.

Feature development

Some features development requires changes in CRI API and corresponding changes in Container Runtime. Coordinating between Kubernetes branches and release versions and Container Runtime versions is not always trivial.

The recommended feature development flow is following:

  • Review proposed CRI API changes during the KEP review stage. Some field names and types may not be spelled out exactly at this stage.
  • Locally implement a prototype that implement changes in both - Kubernetes and Container Runtime.
  • Submit a Pull Request for Kubernetes implementing CRI API changes alongside the feature code. Feature must be developed to degrade gracefully when used with older Container Runtime according to the Version Skew policy.
  • Once PR is merged, wait for the next Kubernetes release tag being produced. Find the corresponding CRI API tag (e.g. k8s.io/[email protected]).
  • This tag can be used to implement the feature in Container Runtime. It is recommended to switch to the stable tag like (k8s.io/[email protected]) once available.

Change history

Here is the change history of the Container Runtime Interface protocol:

v1.20

git diff v1.19.0 v1.20.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.21

git diff v1.20.0 v1.21.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

No changes

v1.22

git diff v1.21.0 v1.22.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

  • Windows host process support

    • PodSandboxConfig has windows field of type WindowsPodSandboxConfig
    • New type WindowsPodSandboxConfig introduced
    • New type WindowsSandboxSecurityContext introduced
    • The type WindowsContainerSecurityContext has a new host_process boolean field

  • Feature: add unified on CRI to support cgroup v2

  • The type LinuxContainerResources has a new field unified which is a map of strings

  • Alpha node swap support

    • The type LinuxContainerResources has a new memory_swap_limit_in_bytes int64 field

v1.23

git diff v1.22.0 v1.23.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.24

git diff v1.23.0 v1.24.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.25

git diff v1.24.0 v1.25.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.26

git diff v1.25.0 v1.26.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.27

git diff v1.26.0 v1.27.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.28

git diff v1.27.0 v1.28.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.29

git diff v1.28.0 v1.29.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.30

git diff v1.29.0 v1.30.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

v1.31

git diff v1.30.0 v1.31.0 -- staging/src/k8s.io/cri-api/pkg/apis/runtime/v1/api.proto

Community, discussion, contribution, and support

Learn how to engage with the Kubernetes community on the community page.

You can reach the maintainers of this repository at:

Code of Conduct

Participation in the Kubernetes community is governed by the Kubernetes Code of Conduct.

Contribution Guidelines

See CONTRIBUTING.md for more information. Please note that kubernetes/cri-api is a readonly mirror repository, all development is done at kubernetes/kubernetes.