export and import --mount=type=cache caches

[databus23]

I'm wondering if its possible to save and restore cache mounts. I'm running buildkit in a CI environment where consecutive build of tasks are executed on different worker nodes.
The current --import-cache/--export-cache feature only seems to work on on the resulting layers but does not include the cache mounts.
Is there a way to export and import those cleanly?

[Norbo11]

Also very interested in this - we want to have our CI builds running on Kubernetes pods, and also have the Dockerfiles take advantage of the experimental --mount=cache syntax in order to cache the application's dependencies. However, it's currently unclear how to have our ephemeral pods use such a shared mount on our cluster - I imagined a solution involving PersistentVolumeClaims, however it's unclear how to export/import such cache volumes managed by BuildKit.

[jvanbruegge]

Yes, I just had this issue too with GitHub Actions. As a workaround is it save to cache /var/lib/docker/buildkit/cache.db and is that enough?

[Mahoney]

@jvanbruegge I don't have time to test it right now, but if you find that works could you update https://stackoverflow.com/questions/60448114/how-do-i-reuse-the-cache-from-a-run-mount-type-cache-docker-build with that as an answer?

[tonistiigi]

#1512