What is progressive delivery and how does it extend beyond basic canary releases?

Progressive delivery (a term coined by James Governor) is the evolution of continuous delivery that gives fine-grained control over who receives a new version and monitors impact in real time. Beyond basic canary releases (percentage of traffic), progressive delivery includes: Traffic shadowing (mirroring) — a copy of live traffic is sent to the new version in parallel, with responses discarded, allowing you to observe its behavior under real production load without affecting users; A/B testing — routing specific user segments (by geography, user ID, account plan) to different versions to measure business metric impact; Dark launching — deploying a feature to production but keeping it invisible to users while exercising it with synthetic or mirrored traffic. Tools like Argo Rollouts, Flagger, and LaunchDarkly automate progressive delivery workflows, integrating with Prometheus metrics to automatically promote or abort releases based on error rate and latency SLOs.