SRE Disaster Recovery and Business Continuity

Question 1

What is the difference between RTO (Recovery Time Objective) and RPO (Recovery Point Objective)?

Accepted Answer

RTO is the maximum acceptable time to restore service after a disaster; RPO is the maximum acceptable amount of data loss measured in time (how old the most recent backup can be)

Answer

RTO measures how quickly the team is alerted to a disaster; RPO measures how quickly the first response team arrives on-site

Answer

RTO is the time required to restore from backup; RPO is the time required to validate data integrity after restoration

Answer

Both RTO and RPO measure recovery time; RTO applies to primary systems and RPO applies to secondary systems

Question 2

What is an 'active-active' disaster recovery architecture, and how does it differ from 'active-passive'?

Accepted Answer

Active-active runs identical service instances in multiple regions simultaneously, all serving traffic; active-passive keeps a standby region that is not serving traffic until failover is triggered

Answer

Active-active uses two identical servers behind a load balancer in a single data center; active-passive uses geographically distributed servers

Answer

Active-active requires full data synchronization between all regions; active-passive only synchronizes configuration files

Answer

Active-active is only appropriate for stateless services; active-passive is only appropriate for stateful services

Question 3

Why is it critical to regularly TEST disaster recovery procedures rather than just documenting them?

Accepted Answer

DR procedures drift from reality as systems change — untested plans frequently fail during actual disasters, and regular testing reveals gaps, validates RTOs, and ensures the team has practiced the steps

Answer

DR testing is primarily a compliance requirement and provides limited practical benefit beyond audit documentation

Answer

DR procedures written by experienced engineers are reliable without testing; testing is only needed for procedures written by junior staff

Answer

Testing is only needed when the DR procedure was most recently updated more than 12 months ago

Question 4

A company's DR plan declares a 99.99% availability SLA. Their current backup strategy is daily backups to a single S3 bucket in the same AWS region. What is the MOST critical gap in this plan?

Accepted Answer

Daily backups create an RPO of up to 24 hours, and a single-region backup does not protect against a regional AWS outage — both are incompatible with 99.99% availability

Answer

S3 is not a reliable backup target; the company should use a dedicated backup appliance

Answer

The backup frequency is adequate; the gap is that the company has not documented the restoration procedure

Answer

The SLA only needs backups if the company has signed contracts with financial penalties for downtime

Question 5

What is a 'runbook' in the context of disaster recovery, and what makes it operationally effective?

Accepted Answer

A runbook is a documented, step-by-step procedure for responding to specific failure scenarios; it is effective when it is concrete (exact commands), tested, maintained, and executable by someone unfamiliar with the system

Answer

A runbook is a high-level architecture document describing the recovery architecture for compliance audits

Answer

A runbook is an automated script that runs without human intervention during disaster recovery

Answer

A runbook is a post-incident summary document that captures what was done during the recovery for future reference

Question 6

What is the difference between a 'backup' and 'replication' as data protection strategies?

Accepted Answer

Backups are point-in-time snapshots that protect against accidental deletion and data corruption; replication copies live data to another location in near real-time and protects against site failures but not data corruption

Answer

Backups are stored in the same data center as production; replication always occurs to a geographically distant location

Answer

Backups are immutable; replication creates mutable copies that can be overwritten by the primary

Answer

Backups protect databases only; replication is used for file systems only