Modernizing legacy systems sounds exciting in architecture diagrams. But reality is usually much messier.

Tightly coupled services, shared databases, hidden dependencies, operational risk, delivery pressure, and years of accumulated technical debt make large-scale modernization far more complex than simply “moving to microservices” or “upgrading to .NET Core”.

In this talk, I’ll share lessons learned from modernizing a large-scale .NET platform operating in a high-throughput, highly regulated environment serving millions of users and processing thousands of transactions per second — all while continuing to deliver features and support live production workloads.

Rather than a big-bang rewrite, we adopted an incremental modernization strategy:

modernizing APIs and service boundaries,
extracting selected capabilities into dedicated services,
introducing orchestration layers,
and progressively migrating parts of the platform from .NET Framework to .NET Core.

I’ll cover both the technical and organizational realities of the journey:

what worked well,
what became unexpectedly difficult,
where microservices helped,
where they introduced new complexity,
and why modernization is often more about managing risk and dependencies than technology itself.

This session is not a step-by-step migration tutorial.

It is a practical, experience-driven look at how engineering teams evolve large legacy systems at scale without pausing delivery, disrupting production, or rewriting everything from scratch.

Key Takeaways
Why big-bang rewrites rarely succeed in complex production systems
Practical approaches to incremental .NET modernization
Lessons learned from introducing microservices into legacy platforms
Common migration pitfalls, trade-offs, and hidden complexity
How to balance technical transformation with ongoing business delivery