Legacy System Modernisation

Some systems have earned their place - they just need the freedom to evolve. We help you extend and modernise critical platforms with careful, staged engineering that keeps services running and decisions firmly in your hands.

Expect a practical route forward: open source where it fits, bespoke design where it matters, and measurable progress without the disruption of a full rebuild.

What Is Legacy System Modernisation?

Legacy modernisation is the process of improving or extending existing systems so they can meet today's operational, security, and integration demands. It doesn't always mean replacing core platforms. In many environments, the most reliable path forward is to keep what works, then layer in modern tooling and interfaces around it.

Modernisation can include:

  • Adding APIs and integration layers so systems can exchange data in real time
  • Improving security controls to meet current standards and compliance needs
  • Refactoring or re-platforming specific components to reduce maintenance risk
  • Introducing automation and analytics to reduce manual effort and unlock insights

The goal is straightforward: protect your investment while removing the constraints that slow delivery, increase risk, and block growth.

Platforms & Technologies We Work With

Non-exhaustive - depends on requirements.

  • Integration & APIs

    REST/JSON, API gateways, message queues, GraphQL/gRPC where appropriate

  • Modernisation Approaches

    Strangler pattern, refactoring, re-platforming, modular decomposition

  • Data & Migration

    ETL/ELT, CDC/event streaming, validation & reconciliation, data quality controls

  • Security & Compliance

    IAM/SSO, OAuth/OIDC, secrets management, audit logging

Where Legacy Starts to Hold You Back

When legacy platforms sit at the centre of day-to-day operations, small changes can become big projects: releases slow down, integrations become fragile, and security improvements are constrained by ageing foundations. Costs rise quietly through manual workarounds, duplicated data, and growing reliance on a shrinking pool of specialist knowledge.

We tackle this by working from the edges inwards: establishing clear integration boundaries, modern security controls, and staged upgrades that reduce risk while keeping services live.

With open source tooling where it fits best, we build pragmatic paths from “can't touch it” to “can evolve it”, with clear milestones and measurable outcomes.

Change Becomes High-Risk

Legacy platforms make small updates unpredictable across dependent systems. We isolate change with clear boundaries and staged refactoring to ship safely and repeatably.

Security Gaps Keep Growing

Older stacks often lag on modern auth, encryption, monitoring, and patching. We add current controls that fit your compliance and operations.

Systems Don't Talk Cleanly

Brittle integrations and inconsistent interfaces drive duplicate data and manual fixes. We introduce API and event layers to standardise exchange and reduce coupling.

Reliability Is Too Fragile

Ageing components increase downtime risk and slow incident diagnosis. We boost resilience via incremental re-platforming and stronger observability on critical paths.

Built for the Industries That Cannot Stop

Legacy systems appear across every industry - often in the most critical operational areas. We modernise with the realities of uptime, regulation, and business continuity in mind, designing changes that are supportable and phased to reduce risk.

Telecoms

Improve service continuity and streamline operations while enabling newer platforms and data flows across sites.

E-commerce

Reduce checkout friction, improve stability during peaks, and enable faster platform iteration without destabilising core services.

Healthcare

Strengthen security and compliance while improving interoperability across patient, clinical, and administrative systems.

Education

Improve reliability and performance for student and staff platforms while simplifying management and integration.

Logistics

Enable real-time visibility and workflow automation across fleet, warehouse, and dispatch systems.

Manufacturing

Stabilise production systems, enable predictive insights, and improve continuity across operational technology and enterprise platforms.

Modernisation Outcomes You Can Measure

Modernisation should deliver measurable improvements without forcing risky, all-at-once change. We focus on stability first, then deliver upgrades that create flexibility and future readiness.

How We Deliver Change Without the Drama

We modernise in a way that protects uptime and gives you clear control over scope, risk, and sequencing. Every programme is built around your operational priorities, not a generic template.

  • 1

    Landscape Discovery

    We map your current environment in detail, including system boundaries, dependencies, data flows, and operational constraints. You get a clear view of where risk sits, what is costing time and money, and which improvements will unlock the most value first.

  • 2

    Roadmap & Target Architecture

    We design a staged plan with milestones you can validate, balancing quick wins with longer-term structural improvements. This includes technology choices, integration patterns, sequencing, and clear decision points so you stay in control as priorities evolve.

  • 3

    Incremental Build, Integration & Modernisation

    We implement integration layers, modern interfaces, and targeted component upgrades while keeping production stable. Each change is delivered in manageable steps, with testing, rollback considerations, and operational checks to minimise disruption.

  • 4

    Handover, Enablement & Support Options

    We provide practical documentation, knowledge transfer, and runbooks so your team can operate the modernised environment with confidence. If you want ongoing cover, we can continue through SLA-Based Technical Support or Dedicated Support Hours, tailored to the level of assurance you need.

Why Choose OnyxSis?

People-First Engineering, Not Vendor Theatre

We're a team that stays close to our clients, communicates clearly, and takes ownership when things get complex. You'll work with engineers who value transparency and treat your environment with the care it deserves.

Open Source at Heart, Bespoke by Design

We're passionate about open source and use it thoughtfully to give you flexibility, avoid lock-in, and keep your options open. At the same time, we never force a template - every engagement is shaped around your systems, constraints, and goals.

Evidence You Can Point To

In our Multi-Data Centre Network Transformation case study, we supported a UK telecommunications provider moving from a fragile, single-hosting-provider setup to a resilient, cloud-native architecture. The outcome delivered over 96% fewer unplanned outages and 24% lower annual hosting costs.

Those results weren't accidental - they came from disciplined sequencing, clear operational ownership, and engineering decisions made with longevity in mind. It's the same standard we bring to every modernisation programme, regardless of how tangled the starting point looks.

Support That Sticks With You

After go-live, we stay on hand to bed changes in, tune performance, and keep the operational picture clear as usage grows - so you're not left with a handover document and a hope.

For ongoing assurance, we offer SLA-Based Technical Support and Dedicated Support Hours, giving you a predictable route to advice, fixes, and continuous improvement without restarting procurement.

If you're ready to modernise with confidence and keep full visibility over what's next, share your toughest constraints and we'll turn them into a plan you can deliver.

Talk to Our Team

Frequently Asked Questions

Still have questions? Contact us - our team is here to help.

Upgrade the Edges. Protect the Core

We help you extend critical platforms with APIs, event-driven integration, and selective refactoring - so teams can deliver improvements safely, reduce manual workarounds, and unlock new capabilities.

Plan your next upgrade