I experimented with the syntax directive and successfully built an articlequality image using docker build with a blubber.yaml file.

Here is the workflow I used:

1. Add directive to blubber file:

# syntax=docker-registry.wikimedia.org/repos/releng/blubber:v0.12.1

2. Build image:

$ cd machinelearning-liftwing-inference-services
$ docker build --tag kevinbazira/articlequality-fawiki --target production --file .pipeline/articlequality/blubber.yaml .

Things to note:

1. this directive was added to Docker in version 20.10.0.
2. buildkit should be enabled in your environment if it is not, you could use:

$ DOCKER_BUILDKIT=1 docker build --tag kevinbazira/articlequality-fawiki --target production --file .pipeline/articlequality/blubber.yaml .

Change 856880 had a related patch set uploaded (by Ilias Sarantopoulos; author: Ilias Sarantopoulos):

[machinelearning/liftwing/inference-services@main] ci: add new syntax directive for blubber files

https://gerrit.wikimedia.org/r/856880

For M1 (apple silicon) processors docker build will not work with this directive
However by following the bug reported in -> https://phabricator.wikimedia.org/T318866 and the MR in -> https://gitlab.wikimedia.org/repos/releng/blubber/-/merge_requests/15
The following directive works - using a newer version of the buildkit image which supports multiple platforms.
# syntax=docker-registry.wikimedia.org/repos/releng/blubber/buildkit:v0.15.0

and we build the image by specifying the target platform
docker buildx build --target production -f .pipeline/articlequality/blubber.yaml --platform=linux/amd64 . -t TAG_OF_YOUR_CHOICE

as well as
docker build --target production -f .pipeline/articlequality/blubber.yaml -t TAG_OF_YOUR_CHOICE .

Change 856880 merged by jenkins-bot:

[machinelearning/liftwing/inference-services@main] ci: add new syntax directive for blubber files

https://gerrit.wikimedia.org/r/856880