Legacy Modernisation

Two factors usually force the decision. First, **accumulated technical debt**: years of quick fixes, workarounds, and deferred maintenance make the system increasingly expensive to change and risky to touch. Features that should take days take weeks; bugs multiply; developers avoid certain areas of the codebase entirely. Second, **end-of-life dependencies**: vendors drop support for frameworks, libraries, or platforms (think .NET Framework, older database versions, or deprecated cloud services). Once security patches stop, you're exposed to vulnerabilities and compliance failures. Often both factors combine: the technical debt makes upgrading dependencies harder, which delays the inevitable until you're facing an urgent deadline.

Legacy modernisation is a phased, incremental approach to updating older systems without the risk and disruption of a complete rewrite. Using patterns like the Strangler Pattern, legacy components are gradually replaced with modern alternatives while keeping the business running. **Rewrite risks**: 6-18 month development period with limited new features, high failure rate (industry estimates suggest 60-80% of rewrites fail or massively overrun), business disruption during cutover, and loss of undocumented business logic embedded in the old system. **Modernisation benefits**: Business continuity (gradual transition, no big bang), incremental value delivery (ROI starts immediately, not after completion), reduced risk (smaller changes, easier rollback), and preserved business logic (documentation phase captures what currently works). Rewrites are only appropriate when the legacy system is so fundamentally flawed that incremental improvement is impossible - which is rare, and usually a sign of poor earlier architectural decisions.

I focus on planning, architecture, and governance. Your team (or resources you engage) executes the implementation. I assess your ecosystem, design the migration strategy, make key architectural decisions, and then provide ongoing oversight as your team delivers. This gives you senior technical leadership without the cost of a full external development engagement. If your team needs hands-on support for particularly complex components, I can step in, but the default model is governance and guidance rather than implementation.

Yes, significantly. AI-powered tools accelerate legacy system documentation (automatically generating architecture diagrams and dependency maps), policy and standards documentation (months of work reduced to weeks), and code analysis (identifying migration risks and refactoring opportunities). I use AI/MCP agents to analyse codebases, extract business logic, and document undocumented systems. This dramatically reduces the discovery phase and helps your team understand what they're working with before making changes.

Common risks include data loss during migration, functionality gaps in new systems, performance degradation, and losing critical business logic that was never documented. I mitigate these through comprehensive discovery and documentation in the planning phase, establishing testing strategies (parallel running, shadowing, canary deployments), designing phased rollouts with rollback capability, and providing ongoing governance that catches issues early. My oversight role means architectural decisions are validated before your team commits significant effort, and emerging risks are identified and addressed before they become expensive problems.

The assessment and planning phase typically takes 5-10 days, resulting in a comprehensive roadmap and migration strategy. Implementation timelines depend on your team's capacity and the system's complexity, but typically span 6-18 months for full modernisation. AI-augmented documentation significantly accelerates the discovery phase. Implementation follows business priorities, so high-value components are modernised first, delivering ROI throughout the project.

Scope creep is one of the biggest risks in modernisation projects. Stakeholders often see it as an opportunity to add features, fix every historical issue, or redesign everything. I establish clear scope boundaries during the planning phase, distinguishing between "like-for-like migration" (minimum viable modernisation) and "enhancement opportunities" (things we could do but don't have to). This gives you a controlled approach: complete the core migration first, then selectively pursue enhancements. My governance role includes protecting scope, pushing back on mid-project expansions that threaten delivery, and helping stakeholders understand the cost of scope changes.

Modernisation isn't just about swapping old technology for new. Done well, it's an opportunity to address issues that were previously too risky or expensive to tackle. Common opportunities include architectural simplification (removing complexity that accumulated over years), addressing scalability constraints (designing for growth the legacy system couldn't support), improving code quality and maintainability, enabling new functionality that was difficult or impossible on the old platform, and reducing operational costs through modern infrastructure. During the planning phase, I identify these opportunities and help you prioritise which are worth pursuing alongside the core migration versus deferring to a later phase.

It depends on your organisation and the migration complexity, but I generally recommend a hybrid approach. The overall migration benefits from traditional planning: a clear roadmap with milestones, dependency mapping, and phased delivery gates. You need to know where you're going before you start. However, the implementation within each phase works well with Agile practices: iterative delivery, regular feedback, and the ability to adapt as you learn more about the legacy system's quirks. This hybrid gives you the predictability stakeholders need (clear milestones, progress tracking) while retaining flexibility for the inevitable surprises legacy systems present. During the planning phase, I help you design an approach that fits your team's experience and your organisation's expectations.

This comes up frequently. I assess your team's capability during the planning phase and design the roadmap to match their skill level. If skill gaps exist, I have three approaches: (1) **Upskill your team** - I provide architectural coaching and pair with senior developers during the governance phase to build capability; (2) **Augment with contractors** - I help you source and onboard specialist contractors for complex components; (3) **Hands-on intervention** - for particularly complex areas (e.g., data migration, distributed systems patterns), I can step in directly. The governance model is flexible enough to adapt to your team's needs without requiring a full external development engagement.

Total cost depends on system complexity and team capacity, but here's a typical breakdown. **Phase 1 (Assessment & Planning)**: £4,000-10,000 (5-10 days at £800-1,000/day) delivers your migration roadmap and architecture decisions. **Phase 2 (Governance & Oversight)**: £3,200-8,000/month (1-2 days/week retainer), typically spanning 6-12 months, provides ongoing architectural leadership as your team executes. **Implementation** (your team's cost) varies based on team composition and system complexity, but governance significantly reduces risk of overruns and rework. Compare this to the cost of *not* modernising: continued high maintenance costs, slower feature delivery, compliance risks, and eventual forced migration under crisis conditions (which always costs more). Most clients find phased modernisation delivers ROI within 12-18 months through reduced maintenance burden and increased development velocity.

Success metrics should align with your business goals, but typical measures include: **Business metrics** - reduced maintenance costs (% decrease in bug fix time), increased feature velocity (lead time for new functionality), reduced operational risk (security vulnerabilities and compliance issues resolved). **Technical metrics** - test coverage (% of migrated components with automated tests), deployment frequency (reduction in deployment risk/time), system performance (response time, uptime improvements). **Migration progress** - % of legacy components retired, % of business logic documented, architectural decision records (ADRs) completed. I establish these metrics during the planning phase and track them throughout governance, giving you objective evidence of progress and ROI for stakeholder communication.

It depends on your scale, team structure, and operational maturity. Microservices solve specific problems (independent scaling, team autonomy, technology diversity) but introduce complexity (distributed systems, service orchestration, observability). During the planning phase, I assess whether your scale justifies microservices or whether a well-structured monolith (modular monolith pattern) better fits your context. Many organisations over-engineer for scale they don't have; I help you choose the right architecture for your actual needs, not industry trends.

Age alone isn't the issue. A legacy system becomes a business problem when: (1) **Change velocity slows** - new features take weeks instead of days; (2) **Risk increases** - small changes break unrelated functionality; (3) **Costs escalate** - developer time, infrastructure, or vendor support fees spiral; (4) **Talent gaps emerge** - you can't hire or retain developers for obsolete technology; (5) **Compliance exposure** - end-of-life dependencies create security or regulatory risks. If you're experiencing 2+ of these, modernisation planning should start now, before you're forced into a rushed, risky migration by an external deadline.

I've guided legacy modernisations across .NET (Framework to modern .NET), Java (monolith to modular architectures), Ruby/Rails, PHP, and legacy JavaScript frameworks. My approach is platform-agnostic - migration patterns (Strangler Pattern, parallel run, phased cutover) apply regardless of technology. During the assessment phase, I evaluate whether modernisation means upgrading within the same stack (e.g., .NET Framework to .NET 8) or migrating to a different platform entirely. The right answer depends on your business needs, team skills, and long-term strategy - not technology fashion.

Yes. Many legacy modernisation projects are initiated by founders who recognise the business risk but lack the technical depth to plan confidently. I translate technical decisions into business outcomes, help you understand trade-offs, and ensure you're making informed choices about timelines, budgets, and risks. My role includes stakeholder communication and translating progress into language your board and investors understand. You don't need to be technical - you need to trust the person guiding the modernisation.

Simple. First, we schedule a **free 30-minute consultation** where I learn about your legacy system, business goals, and modernisation drivers. If there's a fit, I provide a scoping proposal for **Phase 1 (Assessment & Planning)**, typically 5-10 days at day rate. This phase delivers your migration roadmap, architecture decisions, and implementation guidance. If you proceed with implementation, we discuss **Phase 2 (Governance & Oversight)** - a flexible retainer for ongoing architectural support as your team executes. No long-term commitments; you decide whether to proceed after each phase based on the value delivered.

Engagements follow two phases with different pricing models. **Phase 1 (Assessment & Planning)** is a fixed-scope engagement, typically 5-10 days at day rate (£800-1,000/day), delivering your migration roadmap, architecture decisions, and implementation guidance. **Phase 2 (Governance & Oversight)** is a flexible retainer, typically 1-2 days per week, providing ongoing architectural review, decision support, and risk management as your team executes. The retainer can flex up if critical situations arise, for example, a 2-week intensive period to navigate an emerging risk, with your approval. Contact me to discuss your legacy system challenges and receive a tailored proposal.