60 Days to Modernize Six Years of Code (Without Breaking Anything)

The platform that powered everything was becoming the thing most likely to break everything.

A six-year-old healthcare marketing startup came to us with a problem they’d been putting off for too long. Their entire operation ran on a .NET 4 codebase, and Microsoft’s support window was closing. Security patches were slowing down. The modern tools their competitors were already using? Those required frameworks their legacy code couldn’t touch. New SDKs that would unlock better data integrations? Not happening on .NET 4.

Their investors had started asking questions about platform security that the technical team couldn’t answer with confidence. Every quarter they waited, the gap between where they were and where they needed to be got wider. The codebase that had carried them through six years of growth was now the anchor keeping them behind. Developers were frustrated, too--all their peers on other projects were using better tools to accomplish their tasks quicker.

The Approaches That Failed

They’d already tried fixing this themselves. The first attempt was the “we’ll upgrade it as we go” approach. Fix things opportunistically while building new features. Chip away at the technical debt whenever there was a spare afternoon. Don’t make it a priority, don’t make a plan, but expect it to happen anyway.

It never worked. New features or urgent fixes always won the priority battle. Customer requests were urgent. Migration was important but never urgent enough to actually do. Months passed. Nothing changed.

The second attempt was automated migration tools that promised to do the heavy lifting. Run the assistant, let it convert everything, clean up a few edges, and you’re done in a week. That’s how the marketing described it, anyway.

Reality looked different. Compile errors everywhere. Manual work still needed on almost everything. The “easy button” didn’t exist. The tools could handle the simple conversions, but six years of business logic built into a healthcare platform isn’t simple. Custom authentication flows, data mapping with outdated tooling, integrations with clinical systems; none of that migrates automatically.

So they were stuck in the classic technical debt spiral. Too busy shipping features to fix the foundation, but the foundation was getting shakier by the month. The team knew it needed to happen. Leadership knew it needed to happen. But nobody had 60 days to stop everything and rebuild the plane while it was flying.

How We Approached the Migration

We started by understanding why a healthcare marketing company couldn’t afford migration mistakes. Customer data lives in these systems. Quality requirements don’t care about your deployment schedule. Owners depended on their marketing pipeline continuing to function with zero downtime. You can’t hire developers who’ve never worked in the industry to migrate your healthcare marketing platform and expect them to understand what’s actually at stake.

Our team spent the first week learning their domain before writing any migration code. We needed to understand which parts of the system were load-bearing walls and which were cosmetic. In a codebase this size, touching the wrong component in the wrong order can cascade into problems that take weeks to untangle.

The key decision was prioritizing a plan, then performing incremental migration instead of a big-bang rebuild. Think of it like remodeling a house while the family still lives in it. You do one room at a time, following a blueprint. You never turn off the water. The family eats dinner every night even while the kitchen is getting new cabinets.

We ran the migration in parallel with their ongoing development work. The business didn’t have to stop while IT caught up. Their team kept shipping features. Our team kept migrating infrastructure. The two workstreams ran side by side without stepping on each other.

Weekly demos kept everyone honest. Every Friday, stakeholders saw exactly what had changed, what was working, and what still needed attention. We found a way to visualize the changes and show the rate of progress, even for a non-technical owner. No status reports that obscure problems. No surprises three months in. The truth comes out on demo day, and that’s when you catch issues while they’re still small.

Our baked-in software architecture methodology meant the new architecture was clean from the start. We weren’t just moving old code to a new framework; we were solidifying the foundation it so the next six years wouldn’t create the same problems. Technical debt accumulates when teams take shortcuts under pressure, and it’s a choice to let it accumulate forever. An ongoing clean architecture audit prevents those shortcuts from compounding.

One more thing mattered to this client: they own every line of code we wrote, and 3rd-party dependencies are kept minimal. No proprietary framework locking them into a relationship with some vendor forever. The code is theirs.

60 Days, 40% Faster, Zero Downtime

The migration finished in 60 days. Their application layer now runs 40% faster. Their developers work with modern tooling that makes debugging easier and deploys cleaner. The security questions from investors have answers now.

Most importantly, this happened without a single minute of downtime and without slowing any other development work in progress. Their customers never noticed the migration was happening. All they noticed was that the application got faster and the developers got happier.

The platform that runs their business is no longer a liability. It’s an asset again. They can recruit developers who want to work with modern tools, which matters more than most non-technical founders realize. Try hiring a senior .NET developer who wants to maintain a .NET 4 codebase; you’ll understand the problem quickly.

Integrations and hosting options that were impossible before are now on their roadmap. The .NET 10 framework unlocks SDKs for deeper CRM integrations they’ve wanted for years.

Their CTO put it this way: “We love how Fixation was able to show us the problem, and recommend a solution, at the same time. All we had to do was say ‘yes’.”

Six years of accumulated code. 60 days to modernize it. Zero disruption to the business that depends on it. That’s what incremental delivery with the right methodology looks like in practice.