This option uses AWS DataSync to replicate the on-premises images to the EFS file system over the Direct Connect connection. AWS DataSync is a service that automates and accelerates data transfer between on-premises storage systems and AWS storage services. It can transfer data to and from Amazon EFS, Amazon FSx for Windows File Server, and Amazon S3. To use AWS DataSync, the company needs to deploy an AWS DataSync agent to an on-premises server that has access to the NFS file system. The agent connects to the AWS DataSync service endpoint in the AWS Region where the EFS file system is located. The company can use an AWS PrivateLink interface endpoint to connect to the service endpoint securely and privately over the Direct Connect connection. The company can then create a task in AWS DataSync that specifies the source location (the NFS file system), the destination location (the EFS file system), and the options for the data transfer (such as schedule, bandwidth limit, and verification). AWS DataSync will then perform the data transfer efficiently and securely, using encryption in transit and at rest.

https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-examples.html

The best migration strategy to meet the requirement of minimizing database service interruption before the DNS cutover is to use AWS DMS to migrate data between the two Aurora DB clusters. AWS DMS can perform continuous replication of data with high availability and consolidate databases into a petabyte-scale data warehouse by streaming data to Amazon Redshift and Amazon S31. AWS DMS supports homogeneous migrations such as migrating from one Aurora MySQL DB cluster to another, as well as heterogeneous migrations between different database platforms2. AWS DMS also supports cross-account migrations, as long as the source and target databases are in the same AWS Region3.
The other options are not optimal for the following reasons:
Option A: Taking a snapshot of the existing Aurora database and restoring it in the new account would require a downtime during the snapshot and restore process, which could be significant for large databases. Moreover, any changes made to the source database after the snapshot would not be replicated to the target database, resulting in data inconsistency4.
Option C: Using AWS Backup to share an Aurora database backup from the existing AWS account to the new AWS account would have the same drawbacks as option A, as AWS Backup uses snapshots to create backups of Aurora databases.
Option D: Using AWS Application Migration Service to migrate data between the two Aurora DB clusters is not a valid option, as AWS Application Migration Service is designed to migrate applications, not databases, to AWS. AWS Application Migration Service can migrate applications from on-premises or other cloud environments to AWS, using agentless or agent-based methods.
References:
1: What Is AWS Database Migration Service? - AWS Database Migration Service
2: Sources for Data Migration - AWS Database Migration Service
3: AWS Database Migration Service FAQs
4: Working with DB Cluster Snapshots - Amazon Aurora
5: [Backing Up and Restoring an Amazon Aurora DB Cluster - Amazon Aurora]
6: [What is AWS Application Migration Service? - AWS Application Migration Service]

The correct solution is to use the authenticate-oidc action for the ALB listener rule and configure it with the details of the AWS Directory Service for Microsoft Active Directory directory. This way, the ALB can use OpenID Connect (OIDC) to authenticate users against the directory and grant them access to the intranet web application. The app client in the directory is used to register the ALB as an OIDC client and provide the necessary credentials and endpoints. The callback URL is the URL that the ALB redirects the user to after a successful authentication. This solution does not require any additional services or roles, and it leverages the existing directory accounts for all users.
The other solutions are incorrect because they either use the wrong action for the ALB listener rule, or they involve unnecessary or incompatible services or roles. For example:
Solution B is incorrect because it uses Amazon Cognito user pool, which is a separate user directory service that does not integrate with AWS Directory Service for Microsoft Active Directory. To use this solution, the company would have to migrate or synchronize their users from the directory to the user pool, which is not required by the question. Moreover, the authenticate-cognito action for the ALB listener rule only works with Amazon Cognito user pools, not with federated identity providers (IdPs) that have metadata from the directory.
Solution C is incorrect because it uses IAM as an identity provider (IdP), which is not compatible with AWS Directory Service for Microsoft Active Directory. IAM can only be used as an IdP for web identity federation, which allows users to sign in with social media or other third-party IdPs, not with Active Directory.
Moreover, the authenticate-oidc action for the ALB listener rule requires an OIDC IdP, not a SAML 2.0 federation IdP, which is what IAM provides.
Solution D is incorrect because it uses AWS IAM Identity Center (AWS Single Sign-On), which is a service that simplifies the management of SSO access to multiple AWS accounts and business applications. This service is not needed for the scenario in the question, which only involves a single intranet web application.
Moreover, the authenticate-cognito action for the ALB listener rule does not work with external IdPs that use SAML, such as AWS IAM Identity Center.
Authenticate users using an Application Load Balancer
What is AWS Directory Service for Microsoft Active Directory?
Using OpenID Connect for user authentication