Data stored within instances is not persistent. If you create an instance and populate the instance with data, then the data will only remain in place while the machine is running. The data will survive a reboot. If you shut down the instance, any data it contained will be lost.

To ensure that you do not lose information, take regular backups using mysqldump. If the data being stored is critical, consider using replication to keep a “live” backup of your data in the event of a failure. When creating a backup, write the data to the Amazon S3 service to avoid the transfer charges applied when copying data offsite.

EC2 instances are not persistent. If the hardware on which an instance is running fails, then the instance will be shut down. This can lead to loss of data or service.

If you want to use replication with your EC2 instances to a non-EC2 environment, be aware of the transfer costs to and from the EC2 service. Data transfer between different EC2 instances is free, so using replication within the EC2 environment does not incur additional charges.

Certain HA features are either not directly supported, or have limiting factors or problems that may reduce their utility. For example, using DRBD or MySQL Cluster may not work. The default storage configuration is also not redundant. You can use software-based RAID to improve redundancy, but this implies a further performance hit.