A large-scale ad-serving infrastructure on AWS overcame operational challenges with a hybrid multi-tenant architecture. The previous cellular architecture provided tenant isolation but created scalability, efficiency, and onboarding issues. A new tier-based architecture was designed with cluster-level isolation, using Amazon Route 53 weighted routing and AWS PrivateLink connectivity to improve operational efficiency. This three-level hierarchy allows for independent scaling to address AWS limits, reducing infrastructure setup steps by 80 percent.