The core requirements are low-latency reads and writes for users in both the US and Europe, with real-time data consistency across regions. Amazon Aurora Global Database is the only solution presented that meets these needs. It provides a primary write region and low-latency read replicas in secondary regions. The key feature is write forwarding, which allows applications in secondary regions (Europe) to issue write statements. These writes are transparently forwarded to the primary cluster (US) for execution and then replicated globally, typically in under a second. Option A correctly identifies this architecture and also details a valid, standard procedure for migrating from RDS for MySQL to Aurora with minimal downtime by creating an Aurora Read Replica and then promoting it.

B: Standard RDS for MySQL cross-Region replicas are strictly read-only. There is no native feature to replicate write queries back to the primary, which would create an unsupported and problematic configuration.

C: "Write forwarding" is a feature exclusive to Amazon Aurora, not RDS for MySQL. Additionally, managing bi-directional logical replication between standard RDS instances is complex and not a managed AWS feature.

D: While this option correctly identifies the target architecture (Aurora Global Database), it is less precise than option A. Option A provides a complete solution by including the specific, valid migration steps required to transition from the current state.

1. Amazon Aurora User Guide - Using Amazon Aurora global databases: "An Aurora global database consists of one primary AWS Region where your data is mastered

and up to five read-only

secondary AWS Regions. ... You can use write forwarding to issue write operations from secondary AWS Regions. With write forwarding

write operations issued from reader DB instances in a secondary AWS Region are forwarded to the writer DB instance in the primary AWS Region." (Section: "Using write forwarding in an Amazon Aurora global database")

2. Amazon Aurora User Guide - Migrating data to an Amazon Aurora DB cluster: "To migrate data from an RDS for MySQL DB instance to an Amazon Aurora MySQL DB cluster with minimal downtime

you can create an Aurora Read Replica of your RDS for MySQL DB instance. ... When the replica lag between the RDS for MySQL DB instance and the Aurora Read Replica is zero

you can promote the Aurora Read Replica..." (Section: "Migrating data from an RDS for MySQL DB instance to an Amazon Aurora MySQL DB cluster"

Subsection: "Migrating from an RDS for MySQL DB instance by creating an Aurora Read Replica")

3. AWS Documentation - Working with read replicas for Amazon RDS for MySQL: "You can create a read replica in a different AWS Region from the source DB instance. This is called a cross-Region read replica. ... Cross-Region read replicas are read-only..." (Section: "Cross-Region read replica limitations for MySQL")