Prometheus Alertmanager vs Unleash

Prometheus Alertmanager is in a maintenance-plus-refactor phase. The 0.32 and 0.33 lines are dominated by internal restructuring — the global alert marker replaced by per-aggregation-group markers, types moved out of shared packages, function signatures changed across the codebase — alongside a steady run of dispatcher fixes for contended routes and goroutine leaks. User-facing additions are modest but real: silence annotations in the UI, receiver labels and filtering on the v2 API, and a structured event recorder behind a feature flag.

Two threads run in parallel. The first is unwinding shared mutable state: the global marker removal and the per-group marker introduction are the same fix applied structurally rather than patched, and the dispatcher bugfixes in 0.32.1 and 0.32.2 read as the symptoms that motivated it. The second is tightening the build and integration boundary — compiled UI assets left the repository in 0.32.0, and internal signatures changed with an explicit warning to downstream integrators. Neither is a feature push; both make the project easier to change later.

The event recorder is gated behind --enable-feature=event-recorder, which is the same staging pattern the project used for flags it later promoted or dropped; expect its status to be resolved in the next minor. Whether more of the marker refactor remains is not visible from these notes.