Canary vs shadow deployments: use cases and requirements

This tests whether you understand tradeoffs between user-facing rollouts and silent traffic duplication. Canary routes a small slice of live traffic to the new version to validate errors and latency with limited blast radius, needing load balancers. Shadow mirrors production traffic to an isolated clone without returning responses to users, enabling full-scale performance testing but requiring duplicate compute and careful isolation. Red flag: claiming shadow reduces user-visible blast radius or that canary tests full load without user impact.