The Invisible Rewrite: Modernizing the Kubernetes Image Promoter

This post describes the complete rewrite of kpromo, the Kubernetes image promoter, achieving a 20% codebase reduction and dramatic performance gains with no user-facing changes.

• •The rewrite was split into 9 independent phases covering rate limiting, clean interfaces, a new pipeline engine, provenance verification, vulnerability scanning, signing/replication separation, and legacy code removal.
• •The new pipeline has 7 clearly separated sequential phases (Setup, Plan, Provenance, Validate, Promote, Sign, Attest), eliminating the rate limit contention that caused most production failures.
• •Parallelizing registry reads reduced the plan phase from ~20 minutes to ~2 minutes; a source-check-before-replication optimization reduced steady-state signature work from ~17 hours to ~15 minutes.
• •The effort spanned 40+ PRs and 3 releases (v4.2.0–v4.4.0), deleting 16,000+ lines and adding 10,000+, for a net reduction of ~5,000 lines.