QR Patrol is a multi-tenant SaaS deployment architecture spanning web, application, and database tiers within a shared Securitas data centre, protected by edge security and HAProxy load balancing. Traffic flows from web browsers and mobile apps through DDoS mitigation and TLS termination to stateless app servers, which connect via DB proxy to master-active and slave-failover database nodes backed by RabbitMQ messaging and Redis caching. High availability is ensured through real-time replication to a DR mirror, automated backups, and external identity federation via Entra ID, while infrastructure admin access and vendor management are segregated by role and trust boundary. This architecture demonstrates defence-in-depth for a security-critical patrol management platform serving multiple client sites from a hardened, multi-layered DMZ. Fork this diagram on Diagrams.so to customize tier sizing, add region failover, or adapt the security posture for your own SaaS deployment.