Comment 1 for bug 2039333

Hi Tom.

Indeed, the Ubuntu Docker image in Docker Hub's "Official images" portfolio no longer comprises the riscv64 arch.

To give you some context:
 - the Docker Hub "Official images" portfolio is a gated set of images, controlled via the docker-library/official-images repository [1]
 - this means the "official images" pass through their CI/CD system before getting into Docker Hub
 - in the past, the Ubuntu image was being built within their CI. Their CI was building the image for riscv64, which is nice. But on the other side, this "rebuild" was causing the resulting Ubuntu images to have different digests from the ones we publish to OCIR, ACR and ECR [2] (which btw, do not have riscv64)
 - therefore, in order to preserve digests across registries, we were early adopters of a new docker-library workflow that accepts pre-built OCI images. Therefore, we currently build the official Ubuntu image ourselves and give docker-library/official-images the OCI references instead.

In short, we are now the source of truth for all Ubuntu container images in all registries, including the official one in Docker Hub. However, our build farm hasn't yet enabled riscv64 builds for OCI images. We want to get it, and we should have it. When? That's really a matter of prioritization, and you could help increase its priority by leaving a nudge at https://answers.launchpad.net/launchpad/+question/704943 :)

I hope this helps.
And yes, for the time being, what you're doing is the best alternative.

[1] https://github.com/docker-library/official-images/blob/master/library/ubuntu
[2] https://gallery.ecr.aws/ubuntu/ubuntu