When modernizing a monolithic application into microservices on AWS, which migration strategy should be used?

Refactor is the correct strategy because it involves re-architecting an application, which is necessary when breaking down a monolithic application into microservices. This approach allows for the modernization of the application to leverage cloud-native features and improve scalability and resilience. Rehost (lift and shift) would move the monolithic application to AWS without changing its architecture, thus not achieving microservices. Replatform would involve some optimization for the cloud, like moving from a self-managed database to a managed service, but wouldn't fundamentally change the application's internal structure to microservices. Repurchase means replacing the application with a new, often SaaS, product, which doesn't align with modernizing an existing application into microservices.