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Migration & Modernisation

Legacy System Modernisation

Replacing ageing systems incrementally, so the business keeps running while it happens.

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Overview

Legacy systems are usually load-bearing. They are also frequently the only place certain business rules are written down. That combination makes a full rewrite the highest-risk option available, and it is the one most often proposed.

We prefer the strangler pattern: put a boundary in front of the old system, move one capability at a time behind it, and retire the original piece by piece. The business gets value continuously, and there is never a single date on which everything must work.

What you get

No big-bang cutover

Capabilities move one at a time, each independently valuable and independently reversible.

Rules preserved

Existing behaviour is documented and tested before it is replaced, including the undocumented edge cases.

Value arrives early

The first improvement ships in weeks rather than at the end of a multi-year programme.

Risk stays bounded

If priorities change mid-way, you are left with a working hybrid rather than an abandoned rewrite.

How we work

  1. 01

    Understand

    The system is documented as it behaves today, including the parts nobody can currently explain.

  2. 02

    Prioritise

    Capabilities ranked by business value and technical risk to decide what moves first.

  3. 03

    Strangle

    A routing boundary is introduced and capabilities are replaced behind it, one at a time.

  4. 04

    Retire

    Old components are decommissioned only once nothing depends on them, verified rather than assumed.

Common questions

Is a rewrite ever the right answer?

Occasionally — for small systems, or where the platform is genuinely unsupportable. For anything large and business-critical, incremental replacement is almost always lower risk.

What if nobody understands the old system?

That is common. We reconstruct behaviour from the code, the database and observed traffic, and write characterisation tests before changing anything.

Can you work with older technology?

Yes. We regularly work around .NET Framework, classic ASP, PHP, on-premises SQL Server and similar. The approach matters more than the language.

Often paired with

Ready to talk about legacy system modernisation?

We will tell you what we would do, roughly what it costs, and whether it is worth doing yet.

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