Product Engineering
Legacy Modernisation & Quality Engineering
Rewriting old code is the easy part. The danger is the behaviour nobody remembers depending on. So we start by pinning down what the system does today, with characterisation tests on the paths that matter, then re-architect and migrate one module at a time, checking parity before each cutover.
HOW IT RUNS
From unverified code to a switched-off legacy system
Four phases, from an unverified codebase to modules running in production with tests behind them, and the old ones switched off.
Codebase & Test-Coverage Audit
The system is mapped against what it really depends on, not what the documentation claims. We identify the highest-risk paths, the untested modules, and the approach that suits each module, including modules that should be retired rather than migrated.
DELIVERABLES
- Codebase and dependency map
- Test-coverage gap report
- Risk-ranked module list
- Approach per module, including retire or replace
- Access, SME and test-data checklist
What We Build
Modernisation while the old system still carries the business
Standalone, or paired with a quality engineering layer. Most engagements open with the audit and test coverage, then move into re-architecture.
Application Re-Architecture
Monoliths split along the seams the system actually has, not a default microservices template.
Cloud Migration
Workloads moved onto infrastructure sized for real usage, instead of a lift-and-shift that relocates the same bottlenecks.
Quality Engineering & Test Automation
Characterisation tests that capture today's behaviour, then automated regression suites that keep it honest through the change.
API & Integration Layer
Legacy functions wrapped in APIs, so new systems can use them without anyone touching the legacy code.
Security & Compliance Upgrade
Outdated auth, unsafe data handling and stale libraries fixed inside the programme rather than parked for later.
Four Ways to Move
Pick the migration path by what failure would cost
Not every system should move the same way, and some shouldn't move at all: retiring a module, containing it behind an API or replacing it with an off-the-shelf product are legitimate outcomes. For the rest, these four:
01
Strangler Fig
New functionality grows around the old system and traffic shifts module by module until the legacy core can be switched off. For systems that can't go down and are too risky to rewrite in one go.
02
Parallel Run
Both systems take identical inputs and their results are compared until they agree. Suited to money and compliance, where a quiet mismatch is the worst outcome.
03
Phased Cutover
Modules move on a schedule while the legacy system handles whatever hasn't moved yet. For systems with clean seams between modules and moderate risk tolerance.
04
Full Re-Platform
One coordinated switch. Only sensible for compact systems with a strong test suite behind them.
Where Your Safety Net Stands
You can't safely change what you can't verify
Old code is usually hard to change for one reason: nobody can prove a change broke nothing. Quality work starts from wherever your safety net is today:
01
Untested
Releases rely on manual checking and hope. First move: characterisation tests on the highest-risk paths, before any architecture work.
02
Partially Covered
Some critical paths are tested and the rest is guesswork. First move: extend coverage to whatever the roadmap touches first.
03
Regression-Safe
The suite catches regressions but is too slow or unreliable, so people bypass it. First move: make it fast and stable enough to trust.
04
Continuously Verified
Fast, reliable tests on every change, and a team that ships on them. First move: keep coverage moving with the re-architecture instead of trailing it.
Our Methodology
Tests before the rewrite, every time
Modernising a system means keeping everything it does today working while adding what it needs next. That gets verified with tests before the architecture changes, because an unverified change is just a new kind of risk.
Coverage Before Architecture
High-risk paths get automated tests before any module is re-architected.
Parity Before Cutover
Each migrated module has its outputs reconciled against the legacy system before traffic moves.
Approach Chosen per Module
Strangler, parallel run, phased cutover or re-platform, decided in the audit by what each module can afford to risk.
Real Data, Safely Handled
Migration scripts and tests run against masked production samples, which carry the edge cases synthetic data misses.
Migration Practice
Migrations that survive the undocumented edge cases
Staging never contains the odd record from a decade ago. Production always does.
These five close that gap.
Security by Design
Security debt - weak auth, risky data handling, unpatched libraries - paid down module by module.
Documentation
Business rules dug out of the old code are written down, so they don't vanish along with it.
Incremental Architecture
Small, separate cutovers, so one bad module never stalls the others.
Record-Level Reconciliation
Record-level reconciliation between source and target, with every discrepancy explained before sign-off.
Compliance Readiness
For regulated systems, controls are verified against the new architecture during migration, not after it.
Technology Stack
The modernisation toolkit
No single migration path. The target architecture and tooling follow what the legacy system needs to become and what your team can maintain.
Node.js / Java / .NET
Target languages chosen for your team's skills and the language the legacy codebase is written in.
Re-ArchitectureAWS / Azure / GCP
Cloud targets chosen around existing infrastructure investment and compliance needs.
Cloud MigrationDocker / Kubernetes
Packaging for each service carved out of the old monolith.
Containers & OrchestrationJest / Selenium / Cypress
Test frameworks matched to the interfaces the legacy system exposes: API, web or batch.
Test AutomationChosen per module. Each module's destination is chosen on its own merits.
Re-Architecture
Node.jsJava.NETContainers & Cloud
Docker
KubernetesAWSAzureGCPTesting
Where It Breaks
How modernisation goes wrong
Architecture work usually starts before anyone knows what the system's test coverage really is. That's where it goes wrong:
Rewrites Without a Safety Net
Modules rewritten from assumptions about what they do. Production reveals the undocumented case the rewrite missed.
Big-Bang Cutovers
Everything switches at once, so one defect takes down the whole operation.
The Old System Never Dies
The new platform is live, the legacy one still runs just in case, and you pay twice for infrastructure and licences. Nobody planned the switch-off.
Why Us
How we modernise legacy systems
A rewrite nobody can verify swaps one risk for another. That's why our first deliverable is a test suite, not a new architecture.
01
Characterisation Tests First
Today's behaviour is captured in tests before the architecture changes, so every change is checked, not hoped for.
02
One Module at a Time
Modules migrate incrementally while the legacy system carries the remaining load.
03
Risk Sets the Order
Whatever causes incidents or blocks work moves first, not whatever is easiest to touch.
04
Decommissioning Planned
The old system's data archive, licences and switch-off are planned from the start, not left as an afterthought.
Vertical Focus
What a bad cutover costs, industry by industry
In retail, an old system costs speed. In healthcare or banking, an unchecked change draws a regulator's attention. Planning follows the stakes.
Modernisation for clinical systems
- Clinical record systems rebuilt service by service
- Consent data migrated with record-level reconciliation
- EHR and clinical integrations rebuilt behind APIs
- Telehealth platforms migrated with monitoring in place
Modernisation for regulated finance
- Core banking modules migrated with parallel runs
- Data migrations reconciled for audit
- Transaction workflows checked against production samples
- Legacy functions exposed safely through APIs
Modernisation for connected-vehicle platforms
- Telematics systems rebuilt for real-time data
- Dealer and CRM migrations tested before cutover
- Fleet workflows re-architected for live visibility
- Telemetry pipelines validated against fleet data
Modernisation for plant systems
- Plant ERP modules migrated around production schedules
- Inventory and dispatch workflows re-integrated
- Production-line systems tested against floor conditions
- Legacy plant systems connected to MES through APIs
Modernisation for field operations
- Farm-management systems moved to the cloud
- Offline-first architecture for weak connectivity
- Seasonal planning rebuilt around harvest cycles
- Legacy sensor data opened up through APIs
Modernisation for high-traffic commerce
- Inventory systems rebuilt for real-time sync
- Checkout and order workflows migrated with reconciliation
- Commerce systems tested against peak traffic patterns
- Legacy POS opened up for omnichannel through APIs
FAQs
Modernisation and quality engineering, answered
A codebase audit, characterisation and regression tests, re-architecture, cloud migration, decommissioning and post-migration monitoring. The audit sets the scope.
That depends on the size of the system, how much test coverage exists and how many modules move. The audit produces a module-by-module plan with a deliverable for each phase.
No. Modules migrate incrementally, each with the approach that fits its risk, while the legacy system carries the rest.
No. Some should be retired, some contained behind an API and left alone, some replaced with an off-the-shelf product. The audit says which, module by module.
Source code access, time with the people who know the business rules, masked production-like data, and test environments. Missing rule-holders are the hardest gap to fill, so we look for them first.
It is switched off on a plan: data archived to an agreed format, licences ended, infrastructure retired. Running both indefinitely is a cost, not a safety net.
Ready to change old code
without guessing?
Describe the system and its worst habits. We'll start with a codebase and coverage audit, and come back with a module-by-module plan, including what should be retired instead of migrated.
Have a project in mind?
Start by finding out what it actually does today.