.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. 

Introduction

Authentication services—often referred to as AuthHubs—form the backbone of secure application ecosystems. They manage login workflows, token issuance, session management, and user authorization. However, these services are not immune to obsolescence. As systems scale, architectural limitations of older AuthHubs prompt a shift to microservices and cloud-native models [1].

Unfortunately, transitioning authentication services is high-stakes. Even minimal disruptions can lock users out, compromise security posture, or break critical application flows. Traditional migration strategies like “big bang” cutovers are error-prone and often lead to rollback scenarios.

This paper proposes a safer, controlled migration model using .NET Core microservices to orchestrate a zero-downtime migration. By decoupling routing, tracking pending authentications, and ensuring real-time data consistency, the system enables users to continue authenticating without even knowing a migration is happening behind the scenes [2].

Proposed Framework

Fig. 1 presents the proposed microservices-based architecture, highlighting the Migration Gateway, routing logic layer, and dual AuthHub communication flow.

Fig. 1. Proposed .NET core microservices framework for zero-downtime authentication hub migration. The system includes a migration gateway, routing logic, parallel AuthHub services, a shared authentication store, and background reconciliation service.

The framework is composed of several loosely coupled microservices, each responsible for specific aspects of the migration process:

Migration Gateway

A .NET Core-based API Gateway (as per Microsoft’s microservice best practices [6]) acts as the single entry point for all authentication traffic. It intercepts login and token-related requests and sends them to the Routing Logic layer. This gateway supports horizontal scaling and is typically deployed via Kubernetes or similar orchestrators for resilience.

Routing Logic Layer

This microservice decides which AuthHub should handle the request—legacy or new—based on:

• Migration status flags

• User segmentation

• A/B testing parameters

• Failover triggers

It ensures traffic can be dynamically split using service mesh techniques [10]

Legacy and New AuthHubs

Both AuthHubs run in parallel during the migration window:

• The Legacy AuthHub retains its API shape and behavior.

• The New AuthHub, developed in .NET Core, supports modern token strategies (OAuth2.1, JWT rotation, etc.) and enhanced observability.

Shared Authentication Database

To maintain consistency, both systems write to a common data store, which contains user credentials, tokens, and session metadata. Data duplication is prevented using version tags and timestamp checks [3].

gRPC Reconciliation Service

A gRPC-based background service ensures reconciliation and secure communication between systems [11]. It ensures any edge-case state (e.g., half-completed sessions) is either repaired or escalated to administrators.

Monitoring and Alerting

Cloud-native observability tools (Prometheus, Grafana, ELK) track:

• Migration errors

• Authentication latency

• Success/failure ratios

• Routing accuracy

This layer is crucial for making real-time decisions about rollback or acceleration of cutover.

Explanation of the Framework

Enables Seamless Coexistence

Rather than disabling the old AuthHub and hoping for the best, the framework allows both systems to coexist, minimizing risk while supporting zero-downtime techniques [7].

Granular Control Over Traffic

routing rules can be fine-tuned following domain-driven design principles [8].

• Region-based migration

• User role-based routing

• Canary testing before global rollout

This allows teams to validate the new system under real load.

Shared State Prevents Session Conflicts

Since both AuthHubs write to a common database, users don’t get logged out or lose sessions when their authentication is routed differently mid-session [4], aligning with distributed system patterns [9].

Background Sync Avoids Data Loss

Even if some requests are missed during dual writes or suffer partial failures, the reconciliation service replays or heals these discrepancies, ensuring data integrity.

Platform Agnostic and Modular

Although implemented in .NET Core, the design principles can be applied in any tech stack. Each component is modular and can be swapped or rewritten without disrupting the overall flow.

Literature Review

Pelloe et al. [1]: “Challenges of Migrating Legacy Applications to Microservices”

This study outlines organizational and architectural challenges in modernizing legacy applications but remains focused on theoretical concerns such as system coupling, stakeholder alignment, and migration cost. It does not explore practical runtime approaches for ensuring continuity during live transitions, especially for critical services like authentication.

Our study addresses this limitation by presenting a dual-authentication architecture with a Routing Gateway. This enables real-time, uninterrupted migration of authentication workflows without affecting user sessions or login continuity.

Balalaie et al. [2]: “Microservices Migration Patterns”

The authors propose a structured set of migration patterns like Strangler and API Gateway layering to support modularization. However, the study lacks a focus on real-time request redirection or how such patterns operate under high-authentication-load scenarios, especially for session-sensitive services.

This paper introduces a Routing Logic Layer that dynamically forwards requests to the appropriate AuthHub based on user roles, migration phase, or system health. This fine-grained control enables progressive migrations without complete cutovers.

Bushong et al. [3]: “On Microservice Analysis and Architecture Evolution”

The research explores microservice performance and container orchestration but overlooks state management challenges during migration. Specifically, it lacks strategies for handling ongoing sessions, tokens, or authentication metadata across dual systems.

The current work proposes a shared authentication datastore with gRPC reconciliation. This ensures data consistency, session continuity, and fault recovery, even if write conflicts or failures occur during migration.

TaeiZadeh et al. [4]: “Security Challenges in Microservices Architecture”

While this study explores inter-service communication and access control, it focuses on static architectural security. It does not address the heightened security risks that arise during live migration of authentication components, such as token leakage or broken state propagation.

Our solution implements OAuth2.1-compliant token flows and enforces backward-compatible APIs. It also introduces runtime access monitoring and failover safeguards to preserve security posture throughout the migration.

Neves [5]: “Modernizing Legacy Applications: A Structured Approach”

This paper emphasizes codebase modularity and software refactoring strategies but lacks discussion around executing migrations in production environments without user-facing impact. It stops at system readiness without addressing live cutover mechanics.

The proposed framework fills this void by allowing both legacy and modern AuthHubs to coexist in production. The seamless routing and background reconciliation ensure zero downtime during live deployment.

Discussion

Enables Seamless Coexistence

Rather than disabling the old AuthHub and hoping for the best, the framework allows both systems to coexist. This minimizes risk and gives teams time to observe the impact of routing logic changes.

Granular Control Over Traffic

Routing rules can be fine-tuned to support:

• Region-based migration

• User role-based routing

• Canary testing before global rollout

This allows teams to validate the new system under real load.

Shared State Prevents Session Conflicts

Since both AuthHubs write to a common database, users don’t get logged out or lose sessions when their authentication is routed differently mid-session [5].

Background Sync Avoids Data Loss

Even if some requests are missed during dual writes or suffer partial failures, the reconciliation service replays or heals these discrepancies, ensuring data integrity.

Platform Agnostic and Modular

Although implemented in .NET Core, the design principles can be applied in any tech stack. Each component is modular and can be swapped or rewritten without disrupting the overall flow.

Experimental Results

We deployed the framework in a sandbox environment simulating a SaaS platform with 1 million users. The experiment included:

• 30,000 login requests/hour

• 60,000 token refreshes/day

• 3 AuthHubs: 1 legacy, 2 new replicas

Metrics:

• Average Authentication Latency: 83 ms

• Routing Accuracy: 99.7%

• Downtime: 0 seconds (verified by simulated heartbeat users)

• Migration Completion Time: 36 hours with progressive rollout

• Reconciliation Success Rate: 98.9% without manual intervention

No failed login spikes, session drops, or authorization mismatches were observed.

Conclusion

Migrating critical authentication services no longer needs to be a risky, high-pressure operation. By leveraging microservice patterns, shared state, and intelligent routing, .NET Core enables a smooth and transparent AuthHub migration path. The design ensures that developers maintain full control, users remain unaffected, and infrastructure teams can monitor every step of the transition.

The combination of stateless services, background reconciliation, and canary traffic management makes this approach scalable and production-safe. It provides a reusable migration blueprint not only for authentication but also for other monolithic-to-microservices transitions.

Discussion of Limitations

Although the framework was thoroughly evaluated in a simulated environment reflecting high authentication traffic, there are inherent limitations due to the absence of real-world deployment variables. Controlled test setups often do not fully reflect the unpredictable conditions of production systems, such as varying network latency, regional failovers, or complex infrastructure dependencies.

In operational settings, factors like delayed database synchronization, inconsistent dual writes, or temporary loss of routing services may introduce session inconsistencies that were not observable during testing. Additionally, security risks specific to transitional states—such as duplicate session tokens or authentication race conditions—require further analysis in real-time, distributed environments.

Moreover, the reconciliation mechanism assumes timely recovery of discrepancies, which may not hold in geographically distributed systems with limited observability or constrained bandwidth. To comprehensively assess the resilience and reliability of this approach, broader validation across live enterprise environments, hybrid deployments, and diverse user populations will be necessary.

Future Work

• AI-Powered Routing Logic: Use ML models to predict AuthHub failures and dynamically adjust traffic.

• Feature-Based AuthHub Switching: Route requests based on feature usage rather than user identity.

• Hybrid Cloud Compatibility: Extend routing to support on-prem AuthHub fallbacks during cloud outages.

• Audit-Centric Migration Logs: Add blockchain-style immutable logs to verify no data loss during migration.

Conflict of Interest

Conflict of Interest: The authors declare that they do not have any conflict of interest.