When servers are down, it can lead to interruptions to your Business objectives and result in loss of revenue. For example, an airline might not be able to book flights for customers if instances and databases are not available. Systems can fail for a variety of reasons, such as fire, human errors, computer failures, disk failures, and programming errors. 

To avoid disruptions and ensure that there is continuity in business services, it is extremely important to have high availability (HA) and disaster recovery (DR) strategies in place. HA and DR are often discussed together. HA is concerned with reducing server downtime as much as possible, but because no system is perfect, DR focuses on the process of using the backup media to recover lost data in the event that the database system does go down.