In a call to buildctl you can specify the frontend which is used to generate the build graph. For example, to build with blubber-buildkit:
buildctl build --frontend=gateway.v0 --opt source=docker-registry.wikimedia.org/repos/releng/blubber/buildkit:v0.16.0 ...
or to build with a Dockerfile:
# Two forms buildctl build --frontend=gateway.v0 --opt source=docker/dockerfile ... # or buildctl build --frontend=dockerfile.v0 ...
For Gitlab CI jobs running on trusted runners, we want buildkitd to enforce use of the blubber frontend.