The main differences between Multi-Availability Zone RDS Database Replication and Failover Versus Read Replicas are that
- Multi-Availability Zones RDS databases are synchronous and provide failover capabilities
- Read replicas are asynchronous – and meant for READING – and do NOT provide failover capability.
You can do both Multi-Zone and Read Replicas simultaneously at an increased cost.
Note: restores from automated (or manual) RDS backups are S3 snapshots – restoration is to a new database and does not overwrite the existing database.