There are two different ways of setting up a redundant MySQL database on Amazon EC2. In both cases, there will be a Master-DB and Slave-DB with replication for failover and recovery. The core difference between each setup is how the backups are saved.
- MySQL-S3 Setup - Backups of the database are saved directly to S3.
- MySQL-EBS Setup - Backups of the database are saved as EBS snapshots to S3. See Overview of MySQL-EBS Setups for more details.

Tutorials
MySQL - S3
MySQL - EBS
MySQL Database Setup Migrations