Legacy software modernization — no big bang, no feature freeze

Not when the software is old, but when it becomes a risk: according to the 2025 Lünendonk study, at one in two companies, continued operation of legacy systems is no longer assured in the medium term. Concrete triggers include expiring support — such as the end of commercial Spring Boot 2.7 support in December 2026 — dwindling talent for the legacy stack, and this rule of thumb: once maintenance costs exceed 50 percent of rebuild costs, replacement belongs on the table.

In most cases, step-by-step modernization beats a rebuild: more than 50 percent of enterprise transformation programs run over budget, while strangler projects fail roughly 40 percent less often than big-bang rewrites. A rebuild makes sense when the business domain has fundamentally changed or the legacy system barely carries any processes anymore. Our assessment runs the numbers on both paths — including the third option of simply keeping the system running.

We publish our price ranges: a first replaceable module at MVP size runs €8,000 to €20,000, a full module replacement with auth and roles €20,000 to €60,000, and the integration layer plus identity setup €5,000 to €20,000. Ongoing modernization on retainer costs €4,000 to €12,000 per month. The upfront assessment is quoted as a fixed price after discovery. Every range comes from real projects.

The cloud providers sort the field into 6R or 7R: rehost, replatform, refactor, rearchitect, rebuild, replace, and retain. For mid-sized companies, two patterns matter most: the strangler fig pattern, where new modules behind a facade replace the legacy system route by route, and two-speed IT, where a fast TypeScript layer ships new features alongside the stable core system. Both avoid the risky big-bang rewrite.

Application modernization is the term coined by cloud providers like Azure, IBM, and Red Hat for the same topic: technically renewing existing applications, usually with a focus on cloud migration and containers. For decision-makers, the label matters less than the question behind it — lowering operational risk, cutting maintenance costs, and regaining the ability to ship without interrupting live operations. That is exactly what the step-by-step approach on this page delivers.

If the system runs stably, there is little need for change, no support deadline is looming, and maintenance costs sit well below 50 percent of rebuild costs, keeping the system running and hardening it is usually the most economical option. We say so openly: if our assessment reaches that conclusion, that exact recommendation goes into the decision document — even when it costs us a modernization project. You pay for a sound decision, not a sales document.

No. With the two-speed approach, the Java core keeps running on its own release cadence while a TypeScript layer next to it ships new features — coupled via APIs and events. We build and run that new layer; your Java core stays with your existing team or vendor, because we deliberately do not offer JVM development. Only what pays off on its own gets replaced — module by module.