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Cloud Application Architectures by George Reese

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Disaster Recovery Planning

Disaster recovery deals with catastrophic failures that are extremely unlikely to occur during the lifetime of a system. If they are reasonably expected failures, they fall under the auspices of traditional availability planning. Although each single disaster is unexpected over the lifetime of a system, the possibility of some disaster occurring over time is reasonably nonzero.

Through disaster recovery planning, you identify an acceptable recovery state and develop processes and procedures to achieve the recovery state in the event of a disaster. By “acceptable recovery state,” I specifically mean how much data you are willing to lose in the event of a disaster.

Defining a disaster recovery plan involves two key metrics:

Recovery Point Objective (RPO)

The recovery point objective identifies how much data you are willing to lose in the event of a disaster. This value is typically specified in a number of hours or days of data. For example, if you determine that it is OK to lose 24 hours of data, you must make sure that the backups you’ll use for your disaster recovery plan are never more than 24 hours old.

Recovery Time Objective (RTO)

The recovery time objective identifies how much downtime is acceptable in the event of a disaster. If your RTO is 24 hours, you are saying that up to 24 hours may elapse between the point when your system first goes offline and the point at which you are fully operational again.

In addition, the team putting together a disaster ...

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