You are the Engineering Manager for a healthcare operations platform that is moving a core service from a single-region setup to a cloud-based, multi-region architecture. The current system supports customer-facing workflows that cannot tolerate extended downtime, and the migration must preserve auditability and data integrity while improving reliability and deployment speed. Product wants the new architecture live before the next customer renewal cycle, Security wants stronger isolation and logging, and Support is already seeing incidents tied to the current infrastructure. The catch is that the team is small, the legacy service has undocumented dependencies, and one senior engineer who understands the current system is only available part-time.