Backup, High Availability, Disaster Recovery, and Migration

This chapter focuses on a lot of different topics, but it really boils down to the availability of services and their resiliency. There are multiple dimensions to achieving the right levels of availability and resiliency, which will be explored in this chapter. There are many aspects to availability and it's important to understand how the aspects fit together to architect the right solution for your organization. Backups often enable us to recover from some kind of human act, such as a deletion of data, corruption, or even attack. This is different from disaster recovery, which is often required in the event of an “act of god,” such as a flood or earthquake. It's important that backup data is stored both close to the source, for optimal restoration, but also far from the source, so that an event at the primary location does not impact both the source and only copy of the backup data. This is achieved by replication of the backup stores. Backup data needs to be as protected as the source data in terms of people that can access the data and encryption. In an ideal world, we hope to never have to use backups, but it's critical they be routinely tested to ensure they could be restored if needed.