Deployment Strategy Pattern Selection — AWS Solutions Architect Pro (SAP-C02)
Blue/Green vs Canary: Instant Rollback vs Exposure Limit
Blue/green and canary deployments both serve the new version to live traffic without taking the application offline, so zero downtime alone does not select between them. Blue/green maintains the full original environment and rolls back by shifting all traffic back; the rollback is instant and complete. Canary limits initial exposure to a percentage of live traffic but cannot undo the experience already delivered to that cohort; rollback stops further exposure, not past exposure. Rolling deployments update instances incrementally and are correct when resource efficiency matters more than rollback speed. 'Immediate full rollback if errors are detected in production' selects blue/green. 'Limit risk to a small percentage of users' selects canary.
What This Pattern Tests
The exam describes a deployment scenario with specific risk and cost constraints. Blue/green maintains two full environments — instant rollback by switching the load balancer, but doubles infrastructure cost during deployment. Canary shifts a small percentage of traffic to the new version, validates with metrics, then shifts the rest — catches issues with limited blast radius but requires health metric automation. Rolling replaces instances in batches — no extra cost but a failed deployment affects batches already updated before detection.
Decision Axis
Rollback speed (blue/green instant vs. canary minutes vs. rolling slow), blast radius (canary smallest), and cost (rolling cheapest).
Associated Traps
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Decision Rules
Choose a CodeDeploy canary or linear Lambda deployment configuration with CloudWatch alarm-triggered automatic rollback over all-at-once or manual alias-flip strategies, because only canary/linear configurations support the pre/post traffic hook evaluation required for sub-60-second alarm-driven rollback without custom out-of-band orchestration.
Domain Coverage
Difficulty Breakdown