Software in the server space is normally fairly stable. However, elements such as security updates and bug fixes must be applied. Highly available servers can't be stopped often, but without important upgrades, they could crash or experience a breach, which would be far more serious.

Then how do we ensure that updates can be applied safely while maintaining consistent availability? Once again, this often comes down to preparation. We prepare by having duplicate online data copies and by abstracting access paths. With architecture like this in place, we can switch to a backup server while upgrading the primary; thus, the database never actually goes offline.

We'll explore this scenario here, especially as it will be a very common one.