Operational Excellence: Disaster Recovery Drill Automation

Act as an AWS Resilience Architect. Create a highly destructive, yet perfectly controlled automated Disaster Recovery (DR) playbook specifically engineered for a massive AWS multi-region environment. The core objective is to programmatically guarantee the infrastructure meets a strict [RTO_TARGET] and an uncompromising [RPO_TARGET] during a total region-loss event. You must write the exact execution logic utilizing [AUTOMATION_SCRIPTS_LANGUAGE] (e.g., a massive Python/Boto3 script orchestrated by AWS Systems Manager Automation). The script must autonomously execute the promotion of secondary cross-region read-replica databases to standalone primary status, and programmatically force the mutation of Route 53 DNS records to sever traffic to the dead zone. Detail the agonizingly complex 'Failback' protocol—the exact mathematical steps required to sync the delta data back to the primary region once it is resurrected, and how to verify absolute data checksum consistency before resuming normal operations.