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23people Legacy Modernization

Modernize Java, .NET Legacy Systems

Legacy system modernization is a 23people service that migrates Java/J2EE, .NET Framework, and PHP monolith platforms to modern cloud-native architectures, using the strangler-fig pattern: module by module, with functional parity validated before each cutover. We operate without stopping client production, and the initial diagnosis is no-commitment.

Strangler Fig, No Downtime

We modernize legacy platforms, migrate to cloud-native architectures, and build custom enterprise applications — incrementally, without interrupting your operation.

Let's Talk About Your Case How We Do It

From Technical Debt to a Platform That Scales

Many organizations run on systems that no longer keep pace with the business: obsolete languages and frameworks, monolithic architectures that are hard to maintain, and critical knowledge concentrated in very few people. We assess your current platform, design a modernization roadmap prioritized by risk and business impact, and execute the migration incrementally — keeping the system in production throughout the entire process.

Part of Enterprise Technology

4–8 wks

Diagnosis and prioritized modernization roadmap

99.8%

Uptime on systems migrated to production

85%

Clients who continue with post-migration support

Why Choose 23people for Legacy Modernization

Incremental Migration, No Downtime

We use the strangler fig pattern to replace legacy functionality module by module, validating each cutover in production before moving to the next. Your operation never stops during modernization.

Reduced Knowledge Risk

We document the business logic that today lives only in legacy code or in the memory of a few key people, reducing your dependency on undocumented tacit knowledge.

Architecture Built to Scale

We migrate toward cloud-native architectures, containers, and microservices when it makes sense for your case — laying the foundation for your platform to support growth without accumulating technical debt again.

Multi-Stack Experience

We work with common enterprise legacy stacks (Java/J2EE, .NET Framework, monolithic PHP) and bring them to modern, maintainable stacks, without locking you into a single vendor or language.

Have a legacy platform that no longer scales? Let's talk, no commitments.

Let's Talk About Your Case

How We Do It

A 4-stage process to modernize your platform without slowing down the business

1. Diagnosis and Risk Mapping

We analyze your legacy code, dependencies, technical debt, and the business risk associated with each module. We identify what to modernize first based on impact and criticality.

2. Modernization Roadmap

We design a prioritized incremental modernization plan, defining what gets refactored, what gets re-platformed, and what gets rewritten — always reviewed with you before execution.

3. Incremental Migration

We execute the migration module by module using the strangler fig pattern: each cutover is validated with functional parity testing before replacing the legacy component in production.

4. Stabilization and Knowledge Transfer

We document the new architecture, put monitoring and observability in place, and transfer knowledge to your internal team so they can operate and evolve the platform going forward.

Start with a diagnosis. No commitment.

Let's Talk About Your Case

Technical Capabilities

Stack and techniques to modernize legacy platforms without disrupting your business

Legacy Stacks We Modernize

  • Java / J2EE
  • .NET Framework
  • Monolithic PHP
  • On-premise systems

Target Architectures

  • Cloud-native (AWS, Azure, GCP)
  • Microservices
  • Containers (Docker / Kubernetes)
  • Serverless where it applies

Modern Development Stack

  • Node.js / TypeScript
  • Python
  • Go
  • React

Migration Techniques

  • Strangler Fig Pattern
  • Database schema migration and modernization
  • API-first refactoring
  • CI/CD pipelines for controlled cutovers

Legacy modernization by stack

Modernization paths for three common enterprise stacks, with incremental cutovers, explicit risk controls, and no big-bang rewrite requirement.

Java/J2EE modernization

Incrementally modernize application-server estates, EJBs, JSPs, and tightly coupled Java enterprise systems.

Explore this guide

.NET Framework modernization

Move IIS, ASP.NET, WCF, Windows services, and .NET Framework dependencies in controlled slices.

Explore this guide

PHP monolith migration

Reduce PHP monolith risk through runtime stabilization, modular boundaries, APIs, and incremental extraction.

Explore this guide

23people Legacy Modernization vs Big-4 Advisory

An honest comparison on the dimensions that matter when choosing a legacy platform modernization partner.

Dimension 23people McKinsey Digital / BCG Platinion Accenture / Deloitte
Multi-year lock-in No — per-scope engagements, no multi-year contracts upfront Yes — typically 2 to 4 year contracts Yes — typically 2 to 4 year contracts
Engineering depth Specialists — we deliver code, not slides Generalists — strategy and diagrams Generalists — execution outsourced to subcontractors
Migration pattern Strangler-fig: module by module, no downtime Variable — sometimes big-bang, sometimes strangler-fig Variable — depends on the assigned team
Pricing model Fixed price per scope or transparent T&M Premium T&M (USD 350-800/hour for senior consultant) Premium T&M plus markup on subcontractors
Specialized focus Legacy + cloud-native + LATAM Multi-vertical — few partners with deep legacy focus Multi-vertical — depends on engagement
Initial diagnosis No-commitment — we deliver the roadmap before any contract Paid — pre-billable, typically USD 100K+ Paid — pre-billable, typically USD 100K+
Client risk Low — pay per deliverable, stop anytime High — pay per hour, costly exit High — pay per hour, costly exit

23people is not a global firm and does not provide M&A advisory or strategy consulting. If your goal is to prepare for due diligence or a multi-year cross-business transformation, Big-4 has capabilities 23people does not seek to replicate. If your goal is to modernize a specific legacy platform without lock-in and with measurable engineering outcomes, 23people is the best risk / outcome option.

Frequently Asked Questions

Straight answers to the most common legacy modernization questions

How do you modernize without stopping operations?
We use the strangler fig pattern: we replace legacy functionality module by module, validating each cutover with functional parity testing before turning off the old component. The legacy and new systems coexist during the transition, so your operation never stops.
Which legacy stacks do you modernize?
We have experience modernizing Java/J2EE, .NET Framework, and monolithic PHP applications, among other common enterprise stacks, migrating toward modern, maintainable cloud-native architectures.
Do you rewrite everything from scratch or refactor?
It depends on the case. We prioritize based on risk and impact: some modules are refactored, others are re-platformed, and we only rewrite from scratch when the cost of maintaining or adapting the legacy code clearly outweighs rebuilding it.
How long does a modernization project take?
The initial diagnosis and prioritized modernization roadmap are completed in 4-8 weeks. The migration itself is executed incrementally, module by module, with production cutovers validated at each stage.
What happens to our internal team?
We don't replace them, we empower them. We document the business logic and the new architecture, and transfer knowledge so your team can operate and continue evolving the platform once the project is complete.
How do you mitigate the risk of losing functionality during migration?
Every migrated module goes through functional parity testing comparing the legacy system's behavior against the new one before the definitive production cutover. This significantly reduces the risk of regressions.

What Our Clients Say

Companies that trust 23people to modernize their technology platform

"Working with 23people is a pleasure due to their human and professional quality, standing out in collaboration and speed."
Ignacio Martínez Corsi
EWS - ICM Service Delivery Manager at Equifax
"I thank 23people for their closeness, understanding and agile management, connecting us with quality professionals and adapting to our needs."
Ester Bravo
Data Strategy and Execution Manager at Equifax
"I value 23people's passion for challenges, working alongside us and delivering results better than expected."
José Pavez
Chief Of Software Development Technological Services Management at ACHS

Success Cases

Modernization without pausing operations

Detailed case study coming soon

We don't yet have a public case study specific to legacy modernization. Check out our other success cases in integrations and cloud, where we have executed modernization projects as part of the scope.

See all cases →
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Let's Talk for 30 Minutes. No Commitments.

Just get to know each other, review your current situation, and see how to you move forward with what you need.

Let's Talk About Your Project

or email us: hello@23people.io