Which design is the LEAST complex to manage after the migration?

Explanations:

Migrating the existing Cassandra database to Amazon Aurora adds complexity due to differences in database architecture, requiring significant changes in how the application interacts with the database. Managing an Aurora database also involves more configuration than DynamoDB, which is a fully managed service.

While Elastic Beanstalk simplifies web server management, migrating Cassandra to EC2 instances increases complexity. The team would have to manage the EC2 instances, including scaling and maintenance, which counteracts the goal of reducing management overhead.

This option provides a balance between ease of management and performance. Migrating to Elastic Beanstalk for the web servers reduces management complexity, and moving to DynamoDB simplifies database management significantly, as it is a fully managed service that eliminates capacity planning and maintenance tasks.

While using Elastic Beanstalk simplifies web server management, migrating to EC2 instances for the web servers increases the management burden, especially as it requires handling Auto Scaling and capacity management manually. DynamoDB is indeed simpler for database management, but the web server setup makes this option less ideal overall.