Legacy .NET modernization services.
Legacy .NET modernization for ASP.NET Web Forms and .NET Framework applications: moved to modern .NET incrementally and in production, one route at a time, without a code freeze and without a rewrite.
ASP.NET Web Forms and .NET Framework applications moved to modern .NET, incrementally and in production, without a code freeze.
- Typical duration
- 3–9 months
- Shape
- Phased, fixed scope per phase
- Starts with
- Modernization assessment
Modernization without the rewrite.
Most modernization projects fail on shape, not on skill. A full rewrite asks a business to run two systems, stop shipping features for a year, and stake everything on a cutover date. We do it the other way: the application is replaced one route at a time while it keeps serving traffic, and every release is small enough to roll back.
What this includes
- Routing boundary so legacy and modern stacks serve one domain
- Unified authentication and session across both stacks
- Route-by-route migration, prioritised by risk and value
- Business logic re-implemented from specification, parallel-run against the original
- Data access modernised: stored procedures reviewed, indexed and instrumented
- Structured logging and health alerting on everything moved
.NET Framework to .NET 10 migration
A .NET Framework application does not have to move to .NET 10 in a single release. Once the routing boundary is in place, the new ASP.NET Core application owns the domain and forwards anything it does not yet handle to the Framework application, so pages, business logic and data access move across in the order set by risk and value.
Each phase is scoped and priced separately, and the work starts from a modernization assessment that sequences it for your specific system.
How a live system gets replaced.
The migration pattern, in the order we use it. It is written out here in full because it is not a secret. The value is in having done it before, not in knowing that it exists.
- 01
Draw the boundary
The legacy application goes behind a single routing layer, so the old stack and the new one serve the same domain, the same cookies and the same users. Nothing has moved yet, but from here anything can, one path at a time.
- 02
Unify the session
Authentication is made to work identically across both stacks before a single page is migrated. A user clicking from a twenty-year-old screen into a new one should not be able to tell, and should never be asked to log in twice.
- 03
Move route by route
Pages are migrated in an order set by risk and value, not by what is convenient. Each release is small, independently deployable and reversible. If a migrated route misbehaves, it goes back, and the rest of the application never notices.
- 04
Parallel-run the logic
Where business rules are re-implemented from specification, both implementations run against the same real inputs and their outputs are diffed until they agree. Rules that have been in production for decades have edge cases nobody remembers; this is how you find them before a customer does.
- 05
Retire, then delete
The old page is removed only after the new one has carried real production traffic. Dead code that is still deployed is not migration. It is two systems to maintain instead of one.
Should you rewrite the system or migrate it?
Migrate it, in almost every case where the system still works. A rewrite concentrates all of the risk on one date and pays nothing back until that date arrives. A route-by-route migration returns value in weeks and lets you stop at any point with the work so far still in production.
| Full rewrite | Route-by-route migration | |
|---|---|---|
| Feature work during the project | Frozen, often for a year | Continues throughout |
| First value in production | At the end, on cutover day | Week three or four |
| If something is wrong | The whole release rolls back | One route rolls back |
| Systems running in parallel | Two, for the entire project | Two, briefly, per route |
| Cutover risk | Concentrated on one date | Spread across many small releases |
| Cost of being wrong | The project | One route |
| When the business sees it | After the money is spent | While it is being spent |
Further reading
- Upgrade
.NET 8 reaches end of support on November 10, 2026: upgrading to .NET 10
.NET 8 and .NET 9 both reach end of support on November 10, 2026, and .NET 10 is where they go next. This is the upgrade in the order it should be done: what to inventory first, the mechanical change, the breaking changes between 8 and 10 that actually bite, and how to release it so it can be taken back.
- Migration
Moving a live ASP.NET Web Forms application to modern .NET
The route-by-route method in full: what has to be true before the first page moves, how one identity and one session are held across two stacks, how re-implemented business logic is proved correct against the original, and what goes wrong. Written to be executed, including by someone who never hires us.
- Validation
Parallel run testing: proving re-implemented business logic
How to be sure a rule you rebuilt from a specification behaves like the one it replaces, when the specification is incomplete and the original is unreadable. Where to run the comparison, what to compare, how to read the differences, and what to do when the old system turns out to be wrong.
Other services
- Multi-tenant platform development
Multi-tenant platforms built end to end, including the operational surface a business needs in order to actually run the thing.
- Modernization assessment
Two weeks, fixed price. A written migration plan for your legacy system that is useful whether or not you hire us to execute it.
- ASP.NET Web Forms migration
ASP.NET Web Forms applications moved to ASP.NET Core and .NET 10 in production, one route at a time, with one login across both stacks and no code freeze.