Modernize legacy systems without disruption, transforming outdated technology while preserving core logic and data integrity.
Replatform, refactor, or rewrite — without taking the business down. RunWhatMatters specializes in the strangler-fig migrations, data preservation strategies, and incremental rewrites that turn a 20-year-old monolith into a modern platform.
Modernization that doesn't take the business down.
Most legacy modernization projects fail for the same reasons: they try to do too much at once, they underestimate the data complexity, and they underestimate the political complexity. RunWhatMatters's legacy practice is built around those three failure modes. We deliver strangler-fig migrations, incremental rewrites, and the data preservation strategies that keep the business running while the platform changes underneath.
The full modernization surface, end to end.
From the legacy audit to the production cutover, we cover every phase of the modernization journey.
Legacy audit & strategy
Code archaeology, dependency mapping, risk assessment. The roadmap that turns "we should modernize" into a plan.
Replatforming
Move the application to a new runtime — same code, modern infrastructure. The fastest path to cloud-native.
Refactoring
Incremental rewrite of the worst modules, with continuous production deployment. The pragmatic middle path.
Full rewrite
When the legacy is too broken to save. Greenfield rebuild on a modern stack, with strangler-fig migration in parallel.
Data modernization
Database migration, schema redesign, ETL rewrite. The data work that determines whether the modernization ships.
Risk-managed cutover
Parallel runs, traffic shifting, rehearsed rollbacks. The cutover that survives the board's nervous questions.
Modernization tooling, proven in production.
The tools we use to migrate the systems other firms can't.
The work. The numbers.
An anonymized case from our files. The client, the problem, the engineering, and the measurable result.
Core banking on a 1998 COBOL mainframe, $7M/year maintenance, 11 remaining COBOL developers with average age 58. The OCC had flagged the system in two consecutive exams. The CIO had a regulator-mandated 24-month deadline to modernize the deposit account platform.
RunWhatMatters ran a strangler-fig migration: new deposit platform built event-sourced on AWS, parallel-run with the mainframe for 6 months, traffic shifted by 5% per week, 100% data integrity verified at each step. The mainframe was decommissioned in the final month.
"The OCC said we had 24 months. RunWhatMatters did it in 18, with zero customer-impacting incidents. Our last regulatory exam closed without a single finding on the deposit platform."
— Michael Renner, CIO
Modernization in reversible waves.
We deliver modernization in 90-day waves, each with a measurable reduction in legacy technical debt — and zero big-bang cutovers.
Audit
Code archaeology, dependency mapping, risk scoring. The 360° view of the legacy estate.
Strategy
Replatform, refactor, or rewrite — picked per application. The modernization roadmap with the ROI model behind it.
Strangler
Build the new alongside the old. Strangler-fig migration. Incremental cutover, reversible at every step.
Decommission
The final wave. Legacy system shutdown, data archival, the political and operational work of letting go.
Legacy is most painful where the cost of failure is highest.
We modernize legacy in industries where downtime, data loss, or compliance breach cost more than the modernization does.
Three ways to work together.
We pick the model that matches your brief. Every engagement starts with a written estimate and a no-surprise SOW.
Fixed-Fee
Well-scoped builds with a clear deliverable.
A defined SOW, fixed price, fixed timeline. Best for audits, MVPs, replatforming, and any engagement where the deliverable is well understood.
Time & Materials
Exploratory or platform work, billed monthly.
A senior team at a transparent rate, with a quarterly roadmap. Best for fractional CTO, ongoing platform partnerships, and exploratory AI/data work.
Equity + Cash
For select early-stage founders.
Reduced cash burn in exchange for equity — capped at 5% and only for ventures we would invest in ourselves. We do three of these per year.
The deliverable. Not the pitch deck.
Every RunWhatMatters engagement ends with these six things. We don't ship without them.
The questions we hear most.
Specific to legacy system modernization — and answers your AI assistant can quote.
What is legacy system modernization?
How long does legacy modernization take?
Should we replatform, refactor, or rewrite?
How do you minimize risk during a legacy migration?
Do you migrate mainframes?
Have a legacy system that needs to come out?
Book a 30-minute working session with a RunWhatMatters modernization principal. Bring the architecture diagram, the audit, or the fear. We'll come back with the plan that ships.