A company is using AWS CodePipeline for the CI/CD of an application to an Amazon EC2 Auto Scaling group. All AWS resources are defined in AWS CloudFormation templates. The application artifacts are stored in an Amazon S3 bucket and deployed to the Auto Scaling group using instance user data scripts. As the application has become more complex, recent resource changes in the CloudFormation templates have caused unplanned downtime. How should a solutions architect improve the CI/CD pipeline to reduce the likelihood that changes in the templates will cause downtime?

This option presents a comprehensive, automated solution that directly addresses the root causes of downtime. Using AWS CloudFormation change sets allows the team to preview the impact of template modifications on existing resources before applying them, preventing unexpected changes. AWS CodeDeploy with a blue/green deployment strategy creates a new, parallel environment (green) to deploy and test the application without affecting the live production environment (blue). Traffic is only switched after successful validation. Integrating automated testing with AWS CodeBuild ensures that both infrastructure and application changes are validated systematically, catching errors early in the pipeline and significantly reducing the risk of production downtime.

A. This approach is reactive and relies on manual testing, which is slow, error-prone, and does not align with modern CI/CD best practices for preventing downtime.

C. Validating templates only checks for syntax errors, not logical issues or the operational impact of resource changes. This option still depends on inefficient manual testing.

D. While introducing a blue/green pattern is an improvement, relying on operators to manually log in and test is not a scalable, repeatable, or reliable validation method for a CI/CD pipeline.

1. AWS CloudFormation User Guide: "With change sets

you can preview how proposed changes to a stack might impact your running resources... before you implement them. Change sets allow you to see how your changes might impact your running resources

for example

if your changes will delete or replace any critical resources." (AWS CloudFormation User Guide

Section: "Updating stacks using change sets").

2. AWS CodeDeploy User Guide: "In a blue/green deployment

a new set of instances (the green fleet) is provisioned

and the new application revision is deployed to it. CodeDeploy reroutes traffic from the original environment (the blue fleet) to the green fleet... After traffic is rerouted

the instances in the blue fleet can be terminated." (AWS CodeDeploy User Guide

Section: "Overview of a blue/green deployment").

3. AWS CodePipeline User Guide: "You can add a test action that uses AWS CodeBuild... to your pipeline. A common use for a test action is to run unit tests on your source code." (AWS CodePipeline User Guide

Section: "Add a test action").

4. AWS Whitepaper - Practicing Continuous Integration and Continuous Delivery on AWS: "AWS CodeDeploy supports blue/green deployments. This deployment strategy helps you minimize downtime... You can also monitor the new application version and roll back the deployment if you encounter any issues." (AWS Whitepapers & Guides

"Practicing Continuous Integration and Continuous Delivery on AWS"

Page 21).