Service
Legacy Modernisation
Moving ageing applications onto a maintainable stack without stopping the business that runs on them.
What this service is
Legacy modernisation is bringing an existing, business-critical application onto a supported platform — by rewriting it, re-architecting it, or progressively replacing parts of it. The defining constraint is that the old system cannot simply be switched off, so the work has to proceed while it keeps running.
The problem
What usually brings people here
An unsupported platform
The framework, runtime or database version no longer receives security updates, and upgrading is blocked by the application itself.
Knowledge held by one person
One developer understands the system, there is no documentation, and that is now a business risk.
Change has become slow and risky
Small modifications take weeks and break things elsewhere, because there are no tests and no clear boundaries.
It cannot integrate
The system holds critical data but offers no API, so everything around it is manual.
Capabilities
What we do
- Assessment of the existing codebase and data
- Modernisation strategy and sequencing
- Incremental migration behind a facade
- Re-platforming to a supported stack
- Data migration and schema redesign
- Adding an API layer to a closed system
- Test coverage around existing behaviour
- Parallel running and phased cutover
Use cases
Typical engagements
Strangler-pattern replacement
New functionality is built alongside the old system and traffic moves across feature by feature, so there is no single high-risk cutover.
Re-platforming
The logic is sound but the runtime, framework or hosting is unsupported, and the application moves without changing behaviour.
Opening up a closed system
An API layer added in front of a legacy application so the rest of the business can integrate with it.
Delivery
How the work runs
- 01
Discovery & requirements
We map how the work actually flows today — the systems, the spreadsheets, the manual handoffs — and agree what success looks like in measurable terms.
- 02
Solution architecture
Data model, service boundaries, integration points and hosting. You get the shape of the system before anyone writes production code.
- 03
UX & technical design
Screens and flows for the people who will use it daily, reviewed against the architecture so the design is buildable as drawn.
- 04
Development & integration
Built in increments you can see and use. Integrations are wired early, because that is where most projects actually go wrong.
- 05
Testing & quality assurance
Automated tests around the logic that matters, plus migration rehearsals against real data shapes before anything goes near production.
- 06
Deployment & onboarding
Release pipeline, environment configuration, data migration and training for the teams who have to live with the system.
- 07
Support & continuous improvement
Monitoring, fixes and the next increment. Software that is used changes; the engagement allows for that.
Technology
What we build with
Backend & APIs
- Java 21
- Spring Boot 3
- Spring Cloud Gateway
- Spring Security
- Python
- REST & webhook APIs
Frontend
- React 19
- Next.js
- TypeScript
- Vite
- Tailwind CSS
Data
- PostgreSQL
- MongoDB
- Redis
- Flyway
- JPA
- Database-per-service
Messaging & storage
- Kafka / Redpanda
- Event streaming
- MinIO & object storage
- Dead-letter queues
Cloud & DevOps
- Azure
- Docker & Compose
- Kubernetes manifests
- GitHub Actions CI
- Static & container hosting
AI & automation
- LLM integration
- Retrieval over business data
- Document extraction
- Workflow orchestration
- Local & cloud inference
Before you commit
What to weigh up
Full rewrites have a poor record: they take longer than planned and the old system keeps changing while you work. Incremental replacement is slower on paper and far more likely to finish. Before anything else, establish test coverage around current behaviour — otherwise you cannot tell a migration from a regression.
Questions
Frequently asked
- Should we rewrite or refactor?
- Refactor and replace incrementally where the logic is still correct and the problem is the platform. A rewrite only makes sense when the business process it encodes has genuinely changed, and even then it should be delivered in stages.
- Can we modernise without downtime?
- Usually. Running old and new side by side with traffic shifted gradually keeps the business operating, at the cost of a period where both must be maintained.
- What if the original developers have gone?
- That is common. We start by reading the code and the data, documenting actual behaviour, and putting tests around it before changing anything.
- How do you reduce migration risk?
- Characterisation tests on existing behaviour, rehearsed migrations against production-shaped data, parallel running with output comparison, and a cutover plan that can be reversed.
Related
You may also need
ERP Development
Implementing, customising or building ERP systems that connect finance, inventory, purchasing and operations.
API & System Integration
Connecting the systems you already run so data moves between them reliably instead of by spreadsheet.
Cloud & DevOps
Deployment pipelines, infrastructure and observability so releases are routine rather than an event.
Talk to us about Legacy Modernisation
Tell us what you want to build, automate or improve, and we'll help you identify the right technical approach.