.NET Core Microservices for Zero-Downtime AuthHub Migrations

Authentication services are critical components in any system architecture. Migrating these services, especially at scale, can be risky due to their direct impact on user login, authorization, and session management. This paper presents a .NET Core microservices-based approach to achieving zero-downtime migrations of AuthHub services, enabling seamless transition between legacy and modern authentication infrastructure. The proposed framework introduces a Migration Gateway and a routing logic layer that intelligently forwards authentication requests to either the legacy or the new AuthHub based on request context, migration progress, or user segment. Built with .NET Core microservices, the system ensures availability, consistency, and backward compatibility through dual write strategies, gRPC reconciliation modules, and shared data storage. We validate the architecture in a high-concurrency environment simulating over 100,000 daily authentications. Our results show zero disruption during migration, consistent session handling, and scalable deployment using container orchestration. The solution proves ideal for organizations looking to modernize authentication without affecting end-user experience.