Release Promotion
Release promotion allows us to ship the same compiled binaries that we’ve already tested.
In the olden days, we used to re-compile our release builds with separate configs, which led to release-specific bugs which weren’t caught by continuous integration tests. This meant we required new builds at release time, which increased the end-to-end time for a given release significantly. Release promotion removes these anti-patterns.
By running our continuous integration tests against our shippable builds, we have a higher degree of confidence at release time. By separating the build phase tasks (compilation, packaging, and related tests) from the promotion phase tasks, we can schedule each phase at their own independent cadence, as needed, and the end-to-end time for promotion is reduced significantly.
Release Promotion Phases
Currently, we have the build, promote, push, and ship phases.
The build phase creates shippable builds. These optimize for correctness
over speed, and are designed to be of shipping quality, should we decide to
ship that revision of code. These are triggered on push on release branches.
(We also schedule depend builds on most branches, which optimize for speed
over correctness, so we can detect new code bustage sooner.)
The promote phase localizes the shippable builds, creates any update MARs,
and populates the candidates directories on S3. (On Android, we rebuild, because
we haven’t been successful repacking the APK.)
The push phase pushes the candidates files to the appropriate release directory
on S3.
The ship phase ships or schedules updates to users. These are often at a
limited rollout percentage or are dependent on multiple downstream signoffs to
fully ship.