What We Learned Migrating a Legacy .NET Framework App to .NET 8
The performance gains were real. The migration path was not as straightforward as the marketing suggests.
Overview
A client came to us with a .NET Framework 4.8 application handling their core order processing, running on infrastructure that was becoming harder to maintain. Here's how the migration to .NET 8 actually went, including the parts that weren't in the official guide.
Article
Auditing dependencies first
Before touching a line of code, we inventoried every NuGet package and third-party library. Roughly a third had no .NET 8 compatible version, which shaped the entire migration timeline more than the framework changes themselves.
The parts that went smoothly
Modern C# language features — records, pattern matching, nullable reference types — made the ported codebase noticeably easier to reason about. Minimal APIs also simplified a handful of internal services considerably.
Where we hit friction
WCF services and anything relying on System.Web required rewrites rather than ports. We budgeted three weeks for this; it took closer to seven. Plan for that gap in any similar migration.
The payoff
Post-migration, the application's median response time dropped significantly and memory usage under load fell as well, largely due to improvements in the .NET 8 runtime and garbage collector.
Key takeaways
- ›Audit third-party dependencies before estimating migration timelines
- ›Budget extra time for WCF and System.Web-dependent code
- ›Modern C# features pay for themselves in reduced maintenance
- ›Runtime and GC improvements alone can justify the migration cost
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