RPO and RTO - modelling recovery objectives

RPO (Recovery Point Objective) and RTO (Recovery Time Objective) are the two numbers that define a backup and DR strategy. This lesson covers how to model them and design a strategy to meet them.

Definitions

• RPO (Recovery Point Objective): how much data loss is acceptable. The age of the most recent backup at the time of disaster. E.g. RPO 1 hour = at most 1 hour of data is lost.
• RTO (Recovery Time Objective): how long recovery takes. The time from disaster to service restored. E.g. RTO 4 hours = service is back within 4 hours.

Calculate RPO from backup frequency

For RPO 15 minutes, you need a 15-minute backup cadence (or continuous replication).

Design RTO

RTO depends on:

• Restore time: how long to recover the data.
• Service setup time: how long to set up the service.
• Validation time: how long to verify the service works.

RTO = restore_time + service_setup + validation

For RTO 4 hours, the sum must be under 4 hours.

Trade-offs

Tighter RPO and RTO cost more. The right level is the minimum that meets the business requirement.

Per-service objectives

Different services may have different objectives:

• Authentication service: RPO 5 min, RTO 1 hour (critical for the whole fleet).
• Internal tooling: RPO 24 hours, RTO 24 hours (low priority).
• Customer-facing: RPO 1 hour, RTO 4 hours (business impact).

Document the objectives per service in the runbook.

Knowledge check