Q: Your company’s primary region (`us-east-1`) completely goes offline (a major AWS outage affecting the whole region). You are tasked with deciding when to trigger the Disaster Recovery failover to `us-west-2`. What metrics/business factors dictate this decision?

A regional failover is the most destructive action an SRE can take; it risks massive data loss, split-brain scenarios, and hours of complex resolution. It should not be triggered lightly.

• Is the outage estimated to last longer than our business-defined RTO? (e.g., if RTO is 4 hours, and AWS says it's an hour fix, we wait. If AWS says ETA unknown, we fail over).
• What is the state of the cross-region database replication? If the replication lag was 2 hours behind when the region died, failing over now guarantees 2 hours of permanent data loss (violating a strict 1-hour RPO).
• We must ensure the us-east-1 environment is completely fenced off (DNS isolated) to prevent a "split-brain" where systems come back online and start writing conflicting data to the old primary database while the new us-west-2 primary is active.

The decision is governed by RTO (Recovery Time Objective) and RPO (Recovery Point Objective):