Toolforge's Harbor instance (image registry) will be down briefly for a version upgrade from 2.9.0 to 2.10.1 tomorrow Thursday 4 April at 9:00 UTC. https://phabricator.wikimedia.org/T354507
If you are using the builds service, you will not be able to run any new builds, or start a job or a webservice from an image built with the build service while Harbor is down. The outage is expected to last a few minutes.
We will send an update before starting maintenance work, and once everything is back up and running.