AppConfig feature flags let Lambda teams roll out changes gradually with automatic rollback

AWS AppConfig feature flags allow switches in Lambda functions to change behavior without redeployment, applying updates in stages rather than to every function at once. The article contrasts this with Parameter Store, where a value change reaches all functions as soon as their cache expires, leaving no safety net for risky features. AppConfig adds schema validation, staged rollout strategies, and rollback triggered by CloudWatch alarms. The author argues Parameter Store suits harmless, rarely changing settings, while AppConfig suits switches that alter behavior. The walkthrough builds a cinema pricing API with CDK and TypeScript, including a gradual rollout and a kill switch.