Over 70% of large enterprise IT budgets are absorbed by maintaining legacy systems. These systems, often critical, cannot simply be 'replaced' — they must be progressively transformed. The question isn't 'should we modernize?' but 'how to modernize without risking the business?'.
4 modernization strategies
Encapsulation (Wrap): expose the legacy via modern APIs without modifying internal code. Fastest and least risky strategy, but doesn't reduce technical debt. Targeted Refactoring: rewrite the most critical or penalizing parts while keeping the rest. Good risk/value balance. Strangler Fig: build the new system in parallel and progressively migrate flows. Preferred for large-scale transformations. Replatform: migration to a packaged solution or cloud platform. Relevant when the business can adapt to a standard.
Case study: banking mainframe migration
A regional bank processed 3 million transactions/day on a 25-year-old COBOL mainframe. Annual maintenance cost exceeded 4M euros. Our Strangler Fig approach over 24 months: exposed the mainframe via an API layer (MuleSoft), progressively migrated business domains to Java/Kotlin microservices on Kubernetes, with mainframe/microservices coexistence and bidirectional synchronization. Result: 70% of transactions migrated, operational cost reduced by 55%, and time-to-market for new products divided by 5.
“Legacy modernization is a marathon, not a sprint. The companies that succeed are those that accept temporary coexistence between old and new.”
— Jose DA COSTA
LegacyModernizationMigrationArchitecture
About the author
JDC
Jose DA COSTA
President & CTO, ACCENSEO
Software engineer with over 15 years of experience in IT consulting and custom development. Jose leads ACCENSEO with a clear vision: making technological innovation accessible to businesses of all sizes.
