Support tiers are defined in REP-2000.
ros2/ci has many different job types
Right now support tiers describe what may block a release, automated testing frequency requirements, and, on platforms where per-package binaries are available, what type of binaries we provide. In the past it’s been easier to add additional nightly jobs for tier 2 platforms rather than create a separate periodic job type. But only the Tier 1 platforms are triggered as part of a pull request review process and even with nightly jobs running that does not mean that our on-call build farmer is required to respond to issues on other platforms. Once the jobs are running on CI we’ll expect that the community members who want to support Debian will do the work of checking the periodic jobs and getting them on par with the other platforms.
