Design a scalable system for managing property access control, considering various access methods (key cards, mobile apps, biometric scanners), real-time authorization, and audit trails for a portfolio of 10,000 properties with 50,000 tenants.

Employ a MECE (Mutually Exclusive, Collectively Exhaustive) framework for a scalable access control system. First, define access methods (key card, mobile, biometric) and their integration protocols (API, SDK). Second, establish a centralized, cloud-native Access Management System (AMS) with microservices architecture for real-time authorization, leveraging OAuth 2.0 and OpenID Connect. Third, implement a robust audit logging service, ensuring immutability and compliance (e.g., SOC 2, GDPR) with event-driven architecture and blockchain for tamper-proof trails. Fourth, design a multi-tenant data model within the AMS, isolating property and tenant data. Fifth, integrate with property management systems (PMS) for automated tenant onboarding/offboarding. Finally, define tiered support and maintenance protocols, including automated alerts and incident response, ensuring 99.99% uptime and data integrity across 10,000 properties and 50,000 tenants.

To design a scalable access control system for 10,000 properties and 50,000 tenants, I would implement a layered architecture leveraging a centralized, cloud-native Access Management System (AMS). This AMS would utilize a microservices approach, allowing independent scaling of components like authorization, authentication, and audit logging. For access methods, we'd support key cards (NFC/RFID), mobile apps (Bluetooth LE, QR codes), and biometric scanners (fingerprint/facial recognition), integrating via standardized APIs. Real-time authorization would be achieved through an event-driven architecture, pushing access policies and revocations instantly to edge devices at each property. A robust, immutable audit trail, compliant with GDPR and CCPA, would be maintained using a distributed ledger or blockchain-like technology for tamper-proof records of every access attempt, successful or failed. Tenant onboarding/offboarding would be automated through seamless integration with the Property Management System (PMS), ensuring immediate provisioning or revocation of access. This system would be designed with multi-tenancy from the ground up, ensuring data isolation and security for each property and tenant, while providing a unified management interface for administrators, significantly reducing operational overhead by 30%.