CodeDeploy Blue/Green: Missing Validation Gate Between Traffic Shift and Fleet Termination

Symptom

When using CodeDeploy blue/green deployments with an Application Load Balancer, traffic shifts from the original fleet to the replacement fleet after the BeforeAllowTraffic lifecycle hook completes. The deployment then enters a configurable termination wait period (default five minutes, maximum one hour) before the original instances are terminated. During this window there is no built-in hook that runs after live traffic reaches the green fleet but before termination begins, so application-level readiness—such as cache warm-up, downstream dependency health, or business transaction success—cannot be validated natively.

Constraints

Teams must either extend the wait time blindly, add external canary analysis with manual approval, or orchestrate a separate Step Functions workflow to fill the gap. The termination wait time is a fixed countdown; it does not pause or reset based on validation outcomes. The BeforeAllowTraffic hook fires before any live traffic reaches the green fleet and cannot exercise real request paths or stateful workflows.

Questions

1. Is there a documented pattern to run custom validation logic against the green fleet after traffic shift but before the termination wait period expires?
2. Can the termination wait time be made conditional on a CloudWatch alarm or synthetic canary result without external orchestration?
3. What is the recommended approach for small applications that cannot justify a full Step Functions canary pipeline?