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Legacy systems modernised slice by slice, without a big-bang cutover.

Legacy applications usually still run the business, which is exactly why they are hard to change. Releases are infrequent, the original authors have moved on and every change needs a regression cycle. We modernise them without stopping them: carving out slices, moving them to a current stack and retiring old code as we go.

A beige tower, CRT monitor and keyboard on a white plinth against a soft grey wall

What we build

Not everything should be rewritten. We assess each component and choose the cheapest route that meets the goal: re-platform what works, decompose what blocks delivery, and rewrite only where the old code costs more to keep than to replace.

Re-platforming to Cloud
We move applications onto containers and managed databases with the minimum code change needed. You get the same behaviour on a supported runtime, automated builds and an environment that can be recreated from code.
Monolith Decomposition
We map domains and dependencies, then extract services behind the strangler pattern, one bounded context at a time. Traffic shifts gradually through routing rules, so each slice can be rolled back on its own.
Targeted Rewrites
Where code is unmaintainable or the platform is end of life, we rewrite the component in a current stack. Behaviour is pinned first with characterisation tests, so the new code matches what users rely on.
Data and Interface Migration
We migrate schemas and data with reconciliation runs, and keep old and new systems in sync through change data capture while slices move. Interfaces are versioned so downstream systems are not broken mid-programme.
Delivery Pipeline Upgrades
Modernised code needs a modern release path. We add CI/CD, automated tests and feature flags as each slice moves, so release frequency improves alongside the architecture, not after it.

How an engagement runs

A typical Application Modernisation engagement runs about 28 weeks from kick-off to a working, handed-over system.

  1. 1

    Code and domain assessment

    We analyse the codebase, dependencies, data and release history, map business domains, and decide per component whether to re-platform, decompose or rewrite.

  2. 2

    Test harness and routing

    We add characterisation tests around the behaviour that matters, set up CI/CD and a routing layer in front of the legacy system, so slices can move safely.

  3. 3

    Slice-by-slice extraction

    In two-week sprints we extract or rebuild one slice at a time, sync data through change data capture, and shift traffic gradually behind feature flags.

  4. 4

    Legacy retirement

    Once traffic and data have moved, we switch off legacy modules, archive what must be kept for compliance, and hand over architecture records and runbooks.

  1. Code and domain assessmentWeeks 0 to 4 of 28

  2. Test harness and routingWeeks 3 to 8 of 28

  3. Slice-by-slice extractionWeeks 7 to 24 of 28

  4. Legacy retirementWeeks 22 to 28 of 28

Weeks from kick-off

Tools and platforms our engineers work in

Languages and frameworks
  • Java
  • Spring Boot
  • .NET
  • Node.js
  • TypeScript
  • Go
  • React
Legacy platforms we work from
  • COBOL
  • .NET Framework
  • Java EE
  • Oracle Forms
  • PL/SQL
Runtime and data
  • Kubernetes
  • Docker
  • PostgreSQL
  • Apache Kafka
  • Debezium
Release tooling
  • GitHub Actions
  • Argo CD
  • LaunchDarkly
  • SonarQube
A rail of folded trousers in a brightly lit clothing store

4x,

More frequent releases

CI/CD and test automation for an omnichannel retailer's e-commerce platform.

Read the case study

How we can work with you

Compare engagement models
  • Assess2–4 weeks

    A 2-4 week code and domain assessment that sets the route for each component and gives you a sequenced plan with effort per slice.

  • Build3–9 months

    A dedicated team modernises slice by slice over 6-9 months, on fixed price per slice or time and materials.

  • Run24x7 SLA-backed run & support

    After cutover we support the modernised application under SLA and keep its dependencies and runtimes patched.

Often combined with

Talk to our Application Modernisation practice

Tell us what you are working on. A practice lead will reply within one working day and can usually scope a discovery within the week.

Talk to Our Team