Zooming in on high availability and disaster recovery

First of all, let's review the difference between high availability and disaster recovery and put that in the Azure context. A high availability (HA) solution is continuously available for a desired amount of time. In Azure, most HA solutions are scoped to a single geographical region.

Disaster recovery (DR) aims to recover from a severe incident, such as a fire (or flooding) in the data center, an earthquake, or any other type of heavy damage. In Azure, an example of a severe outage is the complete unavailability of an entire region, or of a service within a region. DR-compliant systems often rely on multiple regions, which incurs extra costs. Usually, a design that is DR-compliant is also HA.

Whether you design a solution for HA or DR depends on the expected recovery time objective (RTO) and recovery point objective (RPO) defined by the business or expected by your customers (if you provide the service). Figure 3.13...