What separates these images from a distribution’s official ones is not their contents. It is what you can say about them with certainty.

The problem

You boot a cloud image. It came from a mirror, it has a filename and a checksum. The checksum proves the file was not altered after publication. It says nothing about what happened before: which repository, which revision, which machine, which packages at which date, which changes applied after the base install.

On one machine that is a detail. On a fleet it is the layer everything else inherits from, and the only one nobody reads.

What is in place

Reproducible builds. Every image is built by a GitHub Actions workflow from pinned upstream sources and a tagged builder container. The commit, the build run URL and the builder container digest are written into the MANIFEST.json shipped next to the image.

Keyless cosign signatures. Images are signed through GitHub Actions OIDC. There is no private key to keep, so there is no private key to lose. Verification runs against the identity of the workflow that produced the image:

cosign verify-blob alpine-3.23.4-uefi-x86_64.qcow2 \
  --bundle alpine-3.23.4-uefi-x86_64.qcow2.bundle --new-bundle-format \
  --certificate-identity-regexp 'https://github.com/open-img-cloud/' \
  --certificate-oidc-issuer https://token.actions.githubusercontent.com

Immutable paths. The public registry serves images under images.openimages.cloud/<os>/<version>/<filename>. A published path never changes. A mutable latest/ alias exists alongside it for those who want one, but it is never the reference.

Architecture

The build pipeline lives in a shared .github repository as reusable workflows and composite actions. Each image repository stays thin: a VERSION, a customisation script (libguestfs or diskimage-builder depending on the distribution), an upstream version watcher, and two caller workflows.

For storage, the source of truth is a self-hosted Garage cluster, mirrored to Cloudflare R2 and served behind the CDN. A small Worker routes /<os>/* paths to the matching buckets.

Why it matters

The word sovereign is currently sold as a geographic property. But a datacentre in Europe booting images whose lineage nobody can reconstruct gives you no additional guarantee: it moves the trust, it does not remove it.

The point of Open Image Cloud is to make that trust unnecessary. You can verify what you boot without having to believe me.