Here is pretty much the most detailed post about how it works you'll be able to find in public: https://aws.amazon.com/blogs/database/amazon-rds-under-the-hood-

Here is pretty much the most detailed post about how it works you'll be able to find in public: https://aws.amazon.com/blogs/database/amazon-rds-under-the-hood-multi-az/ https://aws.amazon.com/blogs/database/amazon-rds-under-the-h... They basically do replication at the storage layer. Each write has to be acknowledged by both the primary and secondary EBS volume.