Legacy Application Modernization Services
Modernize the applications your business depends on without a big-bang rewrite. Senior engineers rewrite what matters most, keep what works, and build modern API layers around it.
Users keep the same interface
- User interfaceWeb interfaceLive
- OrdersOrdersLive
- ReportingReportingMoving
- BillingQueued
- SchedulingQueued
API LAYER
Original backend
Still running
What Is Legacy Application Modernization?
Legacy application modernization is the work of updating an existing application's code, architecture, interface, or infrastructure so it can keep supporting the business. Legacy application modernization services usually work in stages, so the system keeps running while parts of it change.
You'll also hear it called legacy system modernization or, more broadly, application modernization. Either way, the goal is to change the parts that limit growth and keep the business rules and data that still work.
What counts as a legacy application?
An application that works but can't scale, is hard to maintain, and sits on an outdated stack.
Age isn't the test. A five-year-old app is legacy if every small change takes weeks.
WHEN TO MODERNIZE
Signs Your Legacy Application Is Holding You Back
Most legacy applications still work. The trouble starts when the business needs something they can't do.
Support is about to end
A vendor contract or platform is close to expiring, or access is about to be lost.
It can't scale
The application still works, but it can't grow with the business.
Changes take too long
The code is hard to maintain, and small updates take weeks to release.
The interface slows people down
Training takes too long, and the application doesn't work on mobile.
Security and compliance gaps
The platform can't meet current security or accessibility standards.
It can't connect to anything new
Modern systems and AI tools can't read from it or act on it.
OUR APPROACH
Modernize Without Stopping the Business
Most of what we do is extend the life of good systems. We replace the parts that hold the business back and keep the ones that work.
Rip-and-Replace
- Rewrite the whole system at once
- One large cutover
- Working logic rebuilt from scratch
Incremental Modernization
- Rewrite what matters most
- Keep what works
- Build modern API layers around it
- Preserve the backend where appropriate
- Plan every stage for a zero-downtime transition
What is the strangler fig pattern?
A way to modernize in stages. New components take over one function at a time, behind the same interface, until the old parts can be retired. The old system keeps running the whole time, so each step can be tested and rolled back. It's the pattern JBS Dev uses.
MODERNIZATION PATHS
Choosing the Right Application Modernization Strategy
There are seven common paths. Most systems need more than one, applied to different parts.
| PATH | WHAT IT MEANS | WHEN IT FITS |
|---|---|---|
| Rehost | Move to new infrastructure, usually cloud, with little code change | Infrastructure is the main problem |
| Replatform | Move to a managed platform or newer runtime with targeted changes | Hosting is outdated but the code is sound |
| Refactor | Restructure the code without changing what it does | The code is hard to change but the design still fits |
| Rearchitect | Break a monolith into services or APIs | The design limits scale or speed of change |
| Rebuild | Rewrite on a modern stack, keeping the business rules | The code can't be saved but the logic is valuable |
| Replace | Retire it for an off-the-shelf product | A standard product now does the job |
| Retain | Leave it and connect around it | It works, and changing it costs more than it returns |
How we choose the path
We start with an assessment of the code, integrations, data, and business rules, and we talk to the people who use the system every day. Then senior engineers sort each part: keep it, refactor it, rearchitect it, rebuild it, or replace it. Rearchitecting usually means breaking a monolithic application into microservices or serverless functions, and it only pays off where the design is the bottleneck. Legacy app modernization rarely needs one answer for the whole system. You get a sequenced plan with effort estimates, so you can approve the first stage on its own. Some applications should stay exactly as they are, and the assessment tells you which.
HOW IT WORKS
How a Legacy Modernization Project Runs
Every project starts with a plan your stakeholders approve. Delivery then runs in short, tested releases.
STEP 1
Business Goals
Define outcomes and success measures.
STEP 2
Constraints
Identify technical, operational, and business constraints.
STEP 3
Architecture Review
Evaluate options, assess trade-offs, and align on approach.
STEP 4
Delivery Plan
Detail scope, timeline, resources, and dependencies.
STEP 5
Approved Plan
Stakeholders approve the plan and authorize execution.
Built to be tested
We write tests for all core system components and use continuous integration and delivery (CI/CD) to ship early and often.
What your team gets at handoff
Documentation, training, and hands-on guidance, so your team can run the system without us. Documentation covers the APIs, data mappings, and security approach. Knowledge transfer runs through the project, not only at the end. If you'd rather keep us involved, we also offer maintenance, monitoring, and ongoing development.
WHAT WE MODERNIZE
Legacy Software and Systems We Modernize
Our legacy software modernization services cover five kinds of systems, each one drawn from JBS Dev project work.
Desktop applications
Windows Forms platforms given a modern interface and mobile access, with backend logic preserved.
Legacy databases
Access databases and fragmented data moved to cloud data platforms.
Legacy data migrationAging web platforms
Older Java platforms rebuilt on modern frameworks and AWS serverless services.
Workflow and integration platforms
Proprietary workflow platforms migrated to modern data and workflow platforms such as Azure Data Factory, AWS Glue and Athena, Apache Airflow, Apache Kafka, and Snowflake or Amazon Redshift.
Systems and ERP integrationOperations applications
Spreadsheet-heavy workflows replaced with connected operational platforms.
Modernized from:Windows Forms, Access, Java, proprietary workflow platforms, homegrown systems.
Modernized to:React, Python, Django, .NET on Azure, AWS Lambda and RDS, Microsoft Fabric, Azure SQL.
RESULTS
Legacy Modernization Results
Published examples of JBS Dev changing the systems businesses depend on.
11,000
Employees served by a modernized HR platform
Government
Centralizing Legacy HR Applications for USDA FSIS
Challenge: HR systems more than 15 years old ran on ColdFusion and Microsoft Access, with almost no integration between them.
Result: One Python, Django, and PostgreSQL application replaced the agency's separate HR applications, and support calls dropped significantly.
Read the federal agency case study100+
Workflow jobs migrated in 213 days
Restaurants
Integration Platform Migration for a Top Worldwide Restaurant Chain
Challenge: A costly, unreliable proprietary workflow platform was nearing contract expiration.
Result: More than 100 jobs moved to VisualCron, SSIS, and .NET Azure APIs in 213 days, with estimated annual savings in the hundreds of thousands of dollars.
Read the restaurant chain case studyJBS feels more like an extension of our internal team than a traditional vendor relationship.
Senior IT Leader, AmeriVet Partners
AI-ASSISTED DELIVERY
How AI Speeds Up Legacy Modernization
AI-driven development is a core part of how JBS Dev works. Agentic tooling compresses the routine work, so senior engineers move faster.
Legacy modernization with AI still runs on engineering judgment. AI tools help engineers read old code, trace business rules, draft documentation, and generate tests. Senior engineers review every change and decide what ships.
Modernized systems can connect to AI too. Model Context Protocol (MCP) provides a standard interface between AI tools and existing systems. Access controls, validation, and release approval still need to be designed for the project.
Connecting modernized systems to AI agentsAI-DRIVEN DEVELOPMENT
Agentic tooling
Compresses the routine work
Senior engineers
Review and ship
CONNECTING SYSTEMS TO AI
AI models
Model Context Protocol (MCP)
Standard interface with controlled access
Legacy system
Project-specific integration
Agree on AI data access before work starts
Confirm the approved tools and accounts, the code and data they can access, retention and training terms, review requirements, and who can authorize a release. These are project decisions to document, not assumptions to leave to a tool.
COST AND TIMELINE
What Drives Modernization Cost and Timeline
Start by defining the operational problem and the constraints around it. An assessment establishes what to retain, what to change, and how to phase the work around the systems your business depends on.
- 01Size and complexity of the application
- 02Documentation and test coverage
- 03Number of integrations
- 04Data migration
- 05Security and compliance requirements
- 06How long old and new systems run side by side
Typical timeline
Assessments typically take 2 to 4 weeks. Full production systems typically take 3 to 9 months. Larger programs run in stages, and each stage reaches production on its own. A parallel run, with old and new systems side by side, adds time but lowers the risk at cutover.
How cost is set
Cost follows scope, and the six factors above drive most of it. Engagements are priced as a fixed bid or as time and materials.
ENGAGEMENT MODELS
Ways to Work With Us
Each model stands alone or leads into the next, so you can buy legacy application modernization services one stage at a time.
Assessment & Strategy
For companies that need clarity before committing to a build.
Senior engineers review the application, its integrations, and its data, then give you a modernization roadmap you can act on.
- Technical assessment
- Architecture review
- AI opportunity mapping
- Modernization roadmap
- Prioritized recommendations
Best when: You need to understand the opportunity, risk, architecture, or roadmap before investing in a larger build.
Projects
For companies ready to build or modernize a defined system.
This model is designed for a clearly defined system, workflow, or modernization initiative that needs to be delivered.
- Modernization projects
- Custom applications
- Cloud platforms
- Data systems
- Integrations
- AI agents
Best when: You have a clear business problem, workflow, or platform that needs to be built, modernized, or connected.
Teaming / Managed Delivery
For companies that need experienced delivery capacity.
This option adds experienced delivery capacity to support ongoing development, technical leadership, and execution.
- Senior-led teams
- Embedded engineering
- Ongoing development
- Knowledge transfer
- Flexible support
Best when: You need reliable engineering capacity, technical leadership, or ongoing delivery support without adding unnecessary management overhead.
Modernization stalled? Take over a stalled modernization with Software Project Rescue
WHY JBS DEV
How to Choose a Legacy Modernization Partner
Five questions worth asking any legacy modernization company, and how we answer them.
- Who does the work?
- Senior-level architects, developers, and engineers. No junior bench.
- Will you keep what works?
- Yes. Most of what we do is extend the life of good systems.
- Who owns the result?
- You own everything we build. We don't sell software licenses or another platform.
- How do you avoid disruption?
- We modernize in stages and preserve the backend where appropriate, for a zero-downtime transition.
- How long have you done this?
- JBS Dev has built enterprise software since 1999. Senior US-based engineers lead our builds, with nearshore support available for ongoing work.
JBS Dev is a senior-led custom software development company, founded in 1999, that builds, modernizes, and integrates enterprise systems around the technology clients already own.
FAQ
Legacy Application Modernization FAQs
Short answers to common questions about legacy application modernization services.
What are application modernization services?
Application modernization services update existing software so it can keep supporting the business. The work can include refactoring code, moving to the cloud, rebuilding the interface, adding APIs, or migrating data. JBS Dev's application modernization services change what limits the business and keep the business rules and data that still work.
How do you decide whether to refactor, rearchitect, rebuild, or replace?
We decide part by part, after an assessment. Senior engineers review the code, integrations, data, and business rules, then sort each component into keep, refactor, rearchitect, rebuild, or replace. A full rewrite is the last resort. You get a prioritized, sequenced plan with effort estimates before any build starts.
How long does legacy application modernization take?
Assessments typically take 2 to 4 weeks, and full production systems typically take 3 to 9 months. Larger programs run in stages, and each stage reaches production on its own. For a top worldwide restaurant chain, JBS Dev migrated more than 100 jobs off an expiring workflow platform in 213 days.
How much does legacy application modernization cost?
It depends on scope. The biggest drivers are application size, the state of documentation and tests, the number of integrations, data migration, compliance requirements, and how long old and new systems run side by side. Engagements are priced as a fixed bid or as time and materials, and most start with an assessment.
Can you modernize a live system without downtime?
Yes. That is the point of incremental modernization. New components take over one function at a time while the existing system keeps running. For a bulk liquids logistics provider, a structured transition phase made the move off the legacy system seamless.
How do you modernize code with no documentation or original developers?
Senior engineers recover the business rules from the code itself, then write them down. AI code tools help them read and trace large, undocumented codebases. The documentation and tests produced along the way stay with your team.
What happens to our data during modernization?
Data moves in stages, and each stage is validated before the next one starts. For USDA's Food Safety and Inspection Service, JBS Dev moved separate ColdFusion and Microsoft Access HR applications to one central application on Django and PostgreSQL. The existing system keeps running until the new one is verified. Read more about legacy data migration.
Do we own the code and the intellectual property?
Yes. You own everything we build, along with its documentation. We don't sell software licenses or lock you into another platform.
Can you take over a stalled modernization project?
Yes. Senior engineers start with an assessment of the code, architecture, and delivery process, then stabilize what is there before adding new work. The goal is a credible path to production, whether the project stalled under another vendor or an internal team. See Software Project Rescue.
How do you use AI in legacy modernization?
AI tools help our engineers read old code, trace business rules, draft documentation, and generate tests. Senior engineers review the output and decide what ships. After modernization, Model Context Protocol (MCP) can give AI models a secure, standardized way to read and act on your systems.
INSIGHTS
More on Modernization
Quick Launch Lab
Workshops and assessments
Microservices Decomposition
During this workshop we will focus on integrating completely new microservices as a way to add previously unachievable functionality into an existing monolithic environment.
