Deployment Strategy Pattern Selection — AWS Developer (DVA-C02)
Canary Keeps the Old Version Live During Rollout
CodeDeploy canary and CodeDeploy all-at-once both ship new Lambda versions, but only canary keeps the old version live during the rollout window. Candidates choose blue/green on risk-averse scenarios because it sounds safe. CodeDeploy's canary strategy shifts a small percentage of traffic first, monitors CloudWatch alarms during a configured interval, and rolls back automatically on threshold breach before the remaining traffic moves. Blue/green shifts all traffic at once, which removes the gradual observation window. Instant rollback on error rate spike is a canary behavior, not an all-at-once one. The configured alarm name must match an existing CloudWatch alarm or the rollback trigger never fires.
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
Whether the CodeDeploy deployment group has a CloudWatch alarm explicitly associated so that a metric breach during the canary window triggers an automated traffic revert, versus relying on a parallel full-capacity environment and manual alarm review that inflates cost and removes the automated revert path.
Which CodeDeploy EC2 deployment strategy satisfies both a 75% minimum-capacity availability floor and automated rollback on health-check failure without doubling fleet cost via a second parallel environment.
Whether Rolling with Additional Batch (adds one transient extra batch before retiring old-version instances, preserving the availability floor without duplicating the full fleet) or Immutable (launches a complete parallel Auto Scaling group for every deployment, guaranteeing clean rollback but doubling EC2 fleet size for the entire deployment window) satisfies both the availability SLA and the fixed-budget constraint simultaneously.
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Difficulty Breakdown