Rebuilding the backend of a high-volume claims platform without a freeze
A phased rewrite of core claims processing off unsupported frameworks — delivered while the business kept shipping features and processing claims every day.
- 0
- Feature freezes required
- Phased
- Rollback at every step
- 100%
- Critical paths under test
- Stable
- API contract throughout
A system the business depended on and nobody wanted to change.
Challenge
Core claims processing ran on frameworks years past end of support. Business logic accumulated over a decade sat tangled with the framework itself, so even small changes required tracing behavior by hand.
Constraint
Claims kept arriving. A rewrite-then-switch approach would have meant freezing product work for months, and no one was willing to risk a single big cutover on the pipeline the business bills through.
Cost of inaction
Change velocity was falling, security patches were no longer available upstream, and hiring for the legacy stack was getting harder every quarter — leaving delivery dependent on a handful of specialists.
A migration in phases, each one independently shippable.
Every phase left the platform in a working, releasable state — and every phase could be reversed.
System & dependency map
Before any code moved, we mapped what called what, which paths were load-bearing for claims and payments, and which modules could be changed first with the least blast radius.
Stable API layer in front
Consumers were pointed at a versioned API contract, so internal implementations could be swapped underneath without downstream teams or integrations needing to change.
Regression coverage ahead of each phase
Automated tests were written against existing behavior before it was touched — characterizing the legacy path first, so a rewrite that changed a result was caught immediately instead of in production.
Module-by-module rewrite
Claims intake, adjudication rules, and downstream integrations were migrated onto a supported stack one slice at a time, with old and new coexisting behind the same contract.
Shadow runs & routed cutover
New modules processed real traffic in parallel and were compared against legacy output before taking ownership, then were switched on progressively behind routing controls.
Rollback at every step
Each phase kept the legacy path warm and reversible, so a rollback was a routing change rather than an incident — which is what made continuing feature work safe.
A supported, testable platform — delivered without a feature freeze.
The team ended the engagement on a current stack with automated coverage on the paths that matter, and shipped product work throughout the migration.
Operationally
Changes to claims logic are now routine and covered by tests, instead of requiring a specialist to reason through unsupported framework behavior.
Commercially
Roadmap work never stopped. Feature delivery continued in parallel with the migration, so modernization didn't cost the business a quarter of progress.
Structurally
The API layer and regression suite outlive the project: future replacements can happen behind the same contract, with the same phased, reversible approach.
If you're sitting on a system nobody wants to touch, we can map a phased way out.
A 30-minute call is enough to tell you whether modernization is worth starting now — and we'll say so if it isn't.
Book a 30-min assessment