OCI image
Open Container Initiative Image Spec — standardized format for container images. Descends from Docker v2 manifest, governance moved to OCI in 2017. Ensures an image built with Buildah runs in containerd, CRI-O, Podman etc.
Three parts: manifest (JSON with layer digests), config (JSON with entrypoint, env, labels), layers (tar.gz with diffs). Everything content-addressed via SHA-256. Multi-arch via an image index — points to platform-specific manifests. The registry API (OCI Distribution Spec) was standardized in 2021. The artifact spec extends to non-image content: SBOMs, signatures, Helm charts can live in OCI registries. The ORAS project generalizes this usage.