The Open Container Initiative (OCI) provides a set of industry practices that standardize the use of container image formats and container runtimes. CRI only supports container runtimes that are compliant with the Open Container Initiative.
The OCI provides specifications that must be implemented by container runtime engines. Two important specifications are:
runc—a seed container runtime engine. The majority of modern container runtime environments use runc and develop additional functionality around this seed engine.
OCI image specification—OCI adopted the original Docker image format as the basis for the OCI image specification. The majority of open source build tools support this format, including BuildKit, Podman, and Buildah. Container runtimes that implement the OCI runtime specification can unbundle OCI images and run its content as a container.