Was referring to these features:
Multi-AZ Deployments – A deployment option for your production DB Instances that enhances database availability while protecting your latest database updates against unplanned outages. When you create or modify your DB Instance to run as a Multi-AZ deployment, Amazon RDS will automatically provision and manage a “standby” replica in a different Availability Zone (independent infrastructure in a physically separate location). Database updates are made concurrently on the primary and standby resources to prevent replication lag. In the event of planned database maintenance, DB Instance failure, or an Availability Zone failure, Amazon RDS will automatically failover to the up-to-date standby so that database operations can resume quickly without administrative intervention. Prior to failover you cannot directly access the standby, and it cannot be used to serve read traffic.
Read Replicas – This replication feature makes it easy to elastically scale out beyond the capacity constraints of a single DB Instance for read-heavy database workloads. You can create one or more replicas of a given source DB Instance and serve high-volume application read traffic from multiple copies of your data, thereby increasing aggregate read throughput. Amazon RDS uses MySQL’s native replication to propagate changes made to a source DB Instance to any associated Read Replicas. Since Read Replicas leverage standard MySQL replication, they may fall behind their sources, and they are therefore not intended to be used for enhancing fault tolerance in the event of source DB Instance failure or Availability Zone failure.
Not meaning to imply that AWS is the be-all and end-all of this kind of thing - clearly it isn't.
To get back on track: Does anyone have views / experiences / reviews of the above modules?