Enterprise Software Engineering
Legacy System Modernisation
Incremental modernisation of aging core systems, from mainframe and COBOL to client-server platforms, using strangler-fig migration that keeps the business running.
Overview
Legacy systems persist because they work. They encode decades of business rules, often undocumented, and process transactions the organisation cannot afford to interrupt. The risk is not that they fail tomorrow. It is that every change grows slower, the people who understand them retire, and new capabilities become impossible to add.
We modernise legacy systems incrementally. Rather than a single high-risk rewrite, we use the strangler-fig pattern, change data capture and anti-corruption layers to move capability piece by piece onto a modern architecture, verifying behaviour against the original system at every step.
Business applications
- 01
Core system replacement
Gradually replacing mainframe, IBM i or COBOL-based systems in banking, insurance, logistics and manufacturing, routing functions to new services one capability at a time while the legacy core keeps running.
- 02
Business rule recovery
Extracting undocumented logic from legacy code and stored procedures into readable, tested specifications, giving the organisation back a clear understanding of how its own processes actually work.
- 03
Desktop and client-server migration
Moving Visual Basic 6, Delphi, PowerBuilder or Access applications to web-based architectures without losing the workflows and keyboard-driven efficiency that experienced users depend on every day.
- 04
Data liberation
Exposing data locked in legacy databases and flat files through change data capture and APIs, so new applications and analytics can use it well before the legacy system is retired.
Engineering approach
- 01
System archaeology
We analyse code, data structures, batch jobs, interfaces and operational knowledge to produce a dependency map and an inventory of business capabilities, including the undocumented ones.
- 02
Target architecture and sequencing
We define the target architecture and order the migration by business value, risk and coupling, identifying seams where traffic can be intercepted and redirected safely.
- 03
Strangle incrementally
A routing facade sends selected functions to new services while the legacy system handles the rest, and anti-corruption layers keep legacy data models from leaking into the new design.
- 04
Verify equivalence
Characterisation tests, parallel runs and output comparison confirm that new components produce the same results as the legacy system before any traffic is switched over.
- 05
Decommission deliberately
Once a capability is fully migrated, its legacy code, data and infrastructure are retired with archival and retention requirements met, shrinking the legacy footprint step by step.
Technologies and platforms
Legacy environments
- COBOL
- JCL
- IBM Db2
- RPG
- Visual Basic 6
- Oracle PL/SQL
Migration and data synchronisation
- Debezium
- Apache Kafka
- Kafka Connect
- AWS Database Migration Service
- IBM z/OS Connect
Target platforms
- Java / Spring Boot
- .NET
- Go
- PostgreSQL
- Kubernetes
Verification and observability
- JUnit
- Testcontainers
- Pact
- OpenTelemetry
- Grafana
Technology names are trademarks of their respective owners and do not imply partnership or endorsement.
What you receive
- Legacy dependency map and business capability inventory
- Target architecture and sequenced migration roadmap
- Routing facade and anti-corruption layer for incremental cutover
- Characterisation and parallel-run test harness
- Migrated services kept in sync through change data capture
- Decommissioning plan covering data archival and retention
Questions leaders ask
Why not rewrite the system from scratch?
Full rewrites carry high risk: business rules are rediscovered late, the old system keeps changing during the project, and value arrives only at the end. Incremental modernisation delivers working capability throughout, lets you pause or reprioritise at any point, and keeps the legacy system as a reference for correct behaviour until each piece is retired.
What if nobody fully understands the legacy code anymore?
That is common. We combine static code analysis, inspection of databases and batch jobs, production log analysis and interviews with long-tenured staff to reconstruct behaviour. AI-assisted code comprehension can speed up reading large codebases, but every extracted rule is confirmed through characterisation tests against the running system.
Can the legacy system and new services run side by side?
Yes, and for most of the program they will. Change data capture or event streams keep data synchronised in the required direction, while the routing layer decides which system handles each request. We design this coexistence explicitly, including how discrepancies are reconciled and how a capability can be rolled back if needed.
Related solutions
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- Custom Enterprise Software
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- Mobile Application Development
- SaaS Product Engineering
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- ERP Solutions
- CRM and Business Platforms
- API and Integration Engineering
- Cloud Architecture
- DevOps and Platform Engineering
- Quality Engineering and Testing
- Application Modernisation
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