it involves adding an IPv6 CIDR block to the VPC and subnets for the ALB and specifying the dualstack IP address type on the ALB listener. This allows the ALB to listen on both IPv4 and IPv6 addresses, and forward requests to the EC2 instances that are added as targets to the target group associated with the ALB.

Creating an AWS CodeCommit repository for each project, using the main branch for production code, and creating a testing branch for code deployed to testing will meet the requirements. AWS CodeCommit is a managed revision control service that hosts Git repositories and works with all Git-based tools1. By using feature branches to develop new features and pull requests to merge code to testing and main branches, the developers can avoid code conflicts and lost work, and also implement code reviews and approvals. Option B is incorrect because creating another S3 bucket for each project for testing code and using an AWS Lambda function to promote code changes between testing and production buckets will not provide the benefits of revision control, such as tracking changes, branching, merging, and collaborating. Option C is incorrect because using the main branch for production and test code with different deployment pipelines for each environment will not allow the developers to test their code changes before deploying them to production. Option D is incorrect because enabling versioning and branching on each S3 bucket will not work with Git-based tools and will not provide the same level of revision control as AWS CodeCommit. Reference:
AWS CodeCommit
Certified DevOps Engineer - Professional (DOP-C02) Study Guide (page 182)

EventBridge is needed to detect the database failure. Lambda is needed to promote the replica as it's in another Region (manual promotion, otherwise). Storing and updating the endpoint in Parameter store is important in updating the application. Look at High Availability section of Aurora FAQ: https://aws.amazon.com/rds/aurora/faqs/

The correct answer is D. The scenario requires a solution that can migrate an application from on premises to AWS, run on specific versions of Apache Tomcat, HAProxy, and Varnish Cache, tune the operating system-level parameters, automate the deployment of new application versions, and scale and replace faulty servers automatically. Option D meets all these requirements by using AWS CodeCommit, AWS CodeDeploy, AWS CodePipeline, and Amazon EC2 Auto Scaling. AWS CodeCommit is a fully managed source control service that hosts Git repositories and works with Git-based tools. AWS CodeDeploy is a fully managed deployment service that automates software deployments to a variety of compute services, including Amazon EC2, AWS Fargate, AWS Lambda, and on-premises servers. AWS CodePipeline is a fully managed continuous delivery service that helps automate the release pipelines for fast and reliable application updates. Amazon EC2 Auto Scaling helps maintain application availability and allows scaling of Amazon EC2 capacity up or down automatically according to the defined conditions. By using these services together, the DevOps engineer can migrate the application code to AWS, configure and install the necessary software using the appspec.yml file, automate the deployment process using the pipeline, and scale and replace the servers using the Auto Scaling group.
Option A is incorrect because AWS Fargate is a serverless compute engine for containers that works with Amazon ECS and Amazon EKS. Fargate removes the need to provision and manage servers, but it also limits the ability to tune the operating system-level parameters, which is a requirement in the scenario. Moreover, Fargate does not support HAProxy and Varnish Cache as sidecar containers, which are needed to run the application properly.
Option B is incorrect because AWS Elastic Beanstalk is a fully managed service that automates the deployment and scaling of web applications and services using familiar servers such as Apache, Nginx, Passenger, and IIS. However, Elastic Beanstalk does not support HAProxy and Varnish Cache as part of the Tomcat solution stack, which are needed to run the application properly. Moreover, Elastic Beanstalk web server tier environments are designed to serve HTTP requests, not to process background tasks, which is the purpose of worker tier environments.
Option C is incorrect because AWS Elastic Beanstalk worker tier environments are designed to process background tasks using a daemon process that runs on each Amazon EC2 instance in the environment. Worker tier environments are not suitable for running web applications that serve HTTP requests, which is the case in the scenario. Moreover, Elastic Beanstalk does not support HAProxy and Varnish Cache as part of the Tomcat solution stack, which are needed to run the application properly.
Reference:
AWS CodeCommit
AWS CodeDeploy
AWS CodePipeline
Amazon EC2 Auto Scaling
AWS Fargate
AWS Elastic Beanstalk

Refactor User Data to Use cfn-init and cfn-hup:
cfn-init helps to bootstrap the instance, installing packages and starting services.
cfn-hup is a daemon that can monitor metadata changes and re-apply configurations when necessary.
Example user data script with cfn-init:
#!/bin/bash
yum update -y
yum install -y aws-cfn-bootstrap
/opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource WebServer --region ${AWS::Region}
/opt/aws/bin/cfn-hup
Use Systems Manager State Manager:
State Manager can automatically apply an AWS Systems Manager document to instances at regular intervals, ensuring configurations are kept up-to-date.
Steps:
Create an SSM document that installs and configures your application.
Use State Manager to associate this document with your EC2 instances.
Example SSM document:
{
"schemaVersion": "2.2",
"description": "Install My Application",
"mainSteps": [
{
"action": "aws:runShellScript",
"name": "installApplication",
"inputs": {
"runCommand": [
"yum install -y my-application"
]
}
}
]
}
Create State Manager association:
aws ssm create-association --name "InstallMyApplication" --instance-id <instance-id> --document-version "\$LATEST" Reference:
Using cfn-init and cfn-hup
AWS Systems Manager State Manager