Blue/Green and Canary Deployments

Rolling updates are the right tool most of the time. But rolling updates still route live traffic to both versions during the transition — an acceptable trade-off for most stateless services, and a non-starter for others. Payment processors, auth services, and anything with schema changes don't mix well with "some pods on v1, some on v2" for the three minutes it takes to roll.

Blue/green and canary deployments solve different problems. Blue/green is about the instant cutover: you run v2 in parallel, verify it works, then flip all traffic at once. Canary is about controlled exposure: you route a small percentage of real users to v2 while most traffic stays on v1, then ramp up as confidence builds.