DR Strategies

When RPO and RTO requirements are defined, it's time to select DR strategy:

✏️ Backup\Restore. The simplest option with quite big downtime (RTO) - hours or even days:
- the application runs on a single region only
- regular backups (full and incremental) are sent to another region
- only active region has reserved capacity to run the whole infrastructure
- in case of disaster the whole infrastructure should be rebuilt on a new region (in some cases it can be the same region), after that application is reinstalled and data is restored from backups

✏️ Cold Standby. This option requires less downtime but still it can take hours to fully restore the infrastructure:
- the application runs on a single region only
- minimal infrastructure is prepared in another region: copy of application or data storage may be installed but it's scaled down or run with minimum replicas
- regular backups (full and incremental) are sent to another region
- in case of disaster the application is restored from backups and scaled up appropriately

✏️ Hot Standby. The most complex and expensive option with minimal RTO measured in minutes:
- both regions have the same capacity reserved
- all applications are up and running on both regions
- data is replicated between regions in near real-time
- in case of disaster one of the regions continues to operate.

What to select is usually depends on availability and business requirements of the services you provide. But anyway DR plan should be defined and documented to know what to do in case of disaster. Moreover it's a good practice to provide regular testing on how to restore the system. Otherwise you may end up with the situation when you have a backup but cannot restore the system, or even worse there will be no actual backups at all.

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