A serverless web application is deployed with Lambda functions via CloudFormation. A recent release caused an outage. The deployment process needs to support canary-style releases to shift a portion of traffic to a new Lambda version. Which approach accomplishes this?

The correct approach is to use Lambda aliases with traffic shifting. Lambda aliases allow you to point to different versions of a Lambda function. The update-alias command, specifically with the routing-config parameter, enables you to specify a percentage of traffic to shift to a new version. This directly supports canary deployments by gradually shifting traffic and allowing for rollback if issues arise, without requiring a separate deployment mechanism. Incorrect options: Deploying into a separate CloudFormation stack and using Route 53 weighted routing is overly complex for Lambda versioning and doesn't directly manage the Lambda traffic shift at the function level. The update-function-configuration command does not have a routing-config parameter for traffic splitting between versions; this functionality is managed by aliases. While AWS CodeDeploy can manage Lambda traffic shifting, the question specifies using the AWS CLI for updating the alias, and CodeDeployDefault.OneAtATime is a deployment configuration, not the direct mechanism for canary releases with traffic shifting for Lambda functions.