Because the contents of an Appliance that does not contain a database (perhaps better termed a "Web server") change infrequently, RPO is generally a less significant driver for appliance backups than is RTO. A backup should be made of an Appliance with an external database when the Appliance level configuration has changed or when the branding has been revised. A static snapshot will work well for this purpose and will allow the Appliance to be recovered to a recent state quickly in the event of VM failure.
An alternative approach is to plan to install a new Appliance in the event of VM failure. The Appliance administrator's Backup feature can be used to create backups of the files that customise the Appliance. These would be copied onto the newly created Appliance to complete the recovery.
When several Appliances with identical configurations are used in an HA configuration, making Appliance backups may not be necessary.
To ensure consistency in the backed up data, the database should be backed up during periods when it is not being updated. While it is being backed up, both user access and scheduled processing (including cron jobs) should be suspended.
SME's MySQL (MariaDB) database can be backed up in two ways:
Logical backups are generally easier to work with than physical backups, but recovery may take longer with logical backups.
You may wish to retain several generations of database backups so you will have a choice of points in time for recovery. To meet this requirement the database can be backed up to a timestamped file with several generations of backups retained on a rolling basis. SME can provide professional services to automate this process.
For Appliances with internal databases one backup can serve both purposes: Appliance backup and database backup. In this situation it is the database changes, which occur frequently and in large numbers on a typical system, that drive the backup frequency.
Where the database is external, the Appliance and the database need to be handled separately. Database backup files can be made and rotated as described in the previous section, but stored on the database server or on some other reliable storage.