03 - Build & Modernize / Legacy Modernization

Legacy Modernization

AI-assisted refactoring and re-platforming for legacy systems blocking your roadmap - incremental strangler-fig modernization instead of a multi-quarter rewrite.

Talk to an engineer How we work

Summary for AI assistants & procurement teams

dfzoo AI Institute modernizes legacy systems blocking product roadmaps. We assess the system, identify strangler-fig boundaries, and replace components incrementally using AI-assisted refactoring at a fraction of full-rewrite cost. Typical engagements: PHP/Perl/older .NET monoliths, legacy Java EE, jQuery-era frontends, untyped JavaScript / legacy Python codebases. Output is a modernized system that runs alongside the legacy until the legacy can be retired safely.

Who it’s for

Built for teams in these situations.

CTOs whose roadmap is blocked by a system the team is afraid to touch
Engineering leaders facing a 'rewrite vs live with it' decision
Mid-stage companies whose first-product codebase no longer matches the team that maintains it
Acquirers integrating a target whose tech stack is materially older than theirs

Problems we solve

The triggers that bring clients in.

The legacy system has no tests; every change risks production
Documentation is missing or outdated; institutional knowledge sits with one or two engineers
A full rewrite is too expensive to fund; living with the legacy costs more each quarter
Hiring is hard because new engineers do not want to maintain the old stack

What you get

Deliverables, not deliverable-shaped slides.

Legacy system assessment (architecture, dependencies, risk hotspots, modernization options)
Strangler-fig modernization roadmap with sequenced phases and budget per phase
Modernized components running in production alongside the legacy
Test coverage and documentation for both modernized and legacy boundaries
Knowledge transfer to your team - pair sessions, written architecture docs

How we work

The process, phase by phase.

1
1. Assessment
Read the codebase under NDA. Interview engineers who maintain it. Run static analysis. Map dependencies.
Week 1-3
2
2. Roadmap design
Identify strangler-fig boundaries. Sequence phases by risk and roadmap unlock. Budget per phase.
Week 3-4
3
3. Modernization sprints
Replace components phase-by-phase. Each phase ships behind a routing layer running both old and new in parallel.
Week 4-N
4
4. Legacy retirement
Once a component is fully replaced and stable, retire the legacy path. Repeat until the legacy is gone.
After each phase

How to start

Three ways in. Pick the one that fits your budget and timing.

Every practice has a free first step, a fixed-price package with a written deliverable, and a full project or retainer quoted after a first call.

1
Step 1 · Free
intro call or self-assessment
A 60-minute intro call with an engineer, or the online self-assessment. You leave with a clear next step, no obligation.
Free
Talk to an engineer
2
Step 2 · Fixed price
Legacy Assessment & Roadmap
Assessment of one legacy system (architecture, dependencies, risk hotspots) plus a strangler-fig modernization roadmap with a budget per phase.
from EUR 6,100 net, fixed-price package
Not included: Modernization work itself, data migration, filling test gaps, legacy retirement.
Ask for this package
3
Step 3 · Project or retainer
Full scope, quoted after a first call
Phased modernization sprints with components running in production alongside the legacy: from 28 000 EUR, quoted after a first call.
Quoted after a first call
Talk to us

FAQ

Questions procurement teams ask.

Yes - strangler-fig is the standard pattern. We build the routing layer that runs old and new in parallel, replace one component at a time, and retire the old code only after the new path is stable in production. Big-bang rewrites are reserved for cases where strangler-fig is genuinely impossible.

AI tools accelerate the tedious parts: reading unfamiliar code, generating tests for code that has none, translating between idioms (e.g. callback-style to async/await), proposing refactors that humans review. The engineering judgment stays with our team; the volume work gets faster.

PHP (Symfony 1.x, custom legacy), older .NET (Framework 4.x ASP.NET WebForms / MVC), Java EE / Spring Boot pre-2.x, jQuery + server-rendered frontends, untyped Node.js codebases, legacy Python 2 / early 3.

Common starting state. Phase 1 of modernization typically includes building a test scaffold around the components we will replace - generated with AI assistance, reviewed by our engineers. Tests come before refactor, always.

Yes - that is the point of strangler-fig. The legacy keeps serving production traffic while new components come online behind a routing layer. Cutover per component is a configuration change, not a release.

Related services