Development
Application redesign and modernization of existing software
Redesigning an application means rebuilding or modernizing existing software whose architecture, technologies or usability no longer meet the needs: obsolete versions, abandoned dependencies, code nobody understands anymore, dated interface, exploding maintenance costs. Unlike a simple update, it rethinks the foundations while preserving the data and the usages that work.
Agencei supports companies running a business application, a portal or a product that has become hard to evolve, often built years ago by a vendor or a team that is no longer around.
Our approach favours progressive redesign: audit, stabilization of the existing system, then module-by-module replacement with data migration, so that operations continue throughout the project.
When do we step in?
Every change has become too expensive
Adding a simple feature takes weeks and causes regressions. Maintenance costs exceed what a rebuild on sound foundations would deliver.
The technologies are no longer supported
End-of-life language version, framework or database, with no security patches. Your application becomes a risk for your information system.
The original vendor is gone
Nobody knows the code, documentation is missing, deployment procedures are manual. You no longer dare touch the application.
Performance and usability discourage users
Slowness, an interface incompatible with mobile, journeys designed for usages that have changed: your teams work around the tool with parallel files.
The application must open up to new uses
API for partners, mobile app, cloud hosting, multiplied volumes: the original architecture was not designed for this.
How we work
- 1
Technical and functional audit
Analysis of code, database, infrastructure and actual usage. Inventory of features that are used, ignored or worked around, and of immediate risks.
- 2
Redesign strategy
Choice between in-place modernization, progressive module-based redesign or rebuild, with a batch plan, priority order and estimate per stage.
- 3
Stabilizing the existing system
Before rebuilding, we stabilize: reliable backups, urgent security patches, tests that freeze critical behaviours, reproducible deployment.
- 4
Module-by-module rebuild
Each module is redeveloped on the new foundation, connected to the old system during the transition, and put into service as soon as it is ready.
- 5
Data migration
Cleaning, transformation and transfer of historical data with consistency checks and dry runs before each cutover.
- 6
Decommissioning and stabilization
Shutdown of the old application once all modules have been switched over, period of reinforced monitoring, documentation and handover to your teams.
Technologies we use
- React
- Next.js
- TypeScript
- Node.js
- Java 17 and 21
- Spring Boot
- PostgreSQL
- Data migration tooling
- Docker
- Kubernetes
- AWS
- Characterization tests
Related expertise
Why choose Agencei?
Progressive redesign rather than a big bang
Replacing an entire application at once is the leading cause of failed redesigns. We break the project down to deliver value early and limit risk at every stage.
We start by understanding, not by rewriting
The audit reveals business rules hidden in the code and the features actually used. This is what avoids rebuilding what is no longer needed or forgetting what is essential.
Data handled with the seriousness it deserves
Dry-run migration, consistency checks, rollback plan: your historical data arrives complete and usable in the new application.
Several ecosystems mastered
Java, Node.js, React, PHP, relational and document databases: we can read the old and build the new, whatever the combination.
In brief
- What is this service?
- Audit, planning and delivery service for the redesign of existing applications: technology modernization, progressive module-based rebuild, data migration and decommissioning of the old system.
- Who is it for?
- Companies running a business application, a portal or a product that has become slow, fragile, expensive to maintain or impossible to evolve.
- What problem does it solve?
- Moving away from an obsolete or poorly controlled application without interrupting operations, without losing data and without repeating the original mistakes.
- How long does it usually take?
- Usually from a few months for a modest application to more than a year for a complex system, with modernized modules put into service during the project.
- What factors influence the price?
- Size and condition of the existing code, volume and quality of data to migrate, number of integrations, availability of documentation and of people who know the application, required level of service continuity.
- How does the engagement run?
- Technical and functional audit, choice of redesign strategy, stabilization of the existing system, module-by-module rebuild, data migration with dry runs, decommissioning and stabilization.
- What are the risks?
- A big-bang redesign that fails or drags on, forgotten hidden business rules, incomplete data migration, scope growing by reproducing unused features, user resistance if journeys change too much.
- What alternatives exist?
- Limited modernization (version updates, security hardening, containerization) if foundations are sound, replacement by packaged software if the need has become standard, or keeping the system as is with an end-of-life plan.
Frequently asked questions
Should we rebuild everything or modernize progressively?
It depends on the condition of the code, the quality of the architecture and your constraints. In-place modernization works when foundations are sound but dated. Progressive module-based redesign is preferable in most cases. A complete rebuild is justified when the existing system is beyond recovery, but remains the riskiest option.
Can operations continue during the redesign?
Yes, that is the goal of the progressive approach. Modules are replaced one by one, the old and new systems coexist during the transition, and each cutover is prepared with a rollback plan.
How long does an application redesign take?
From a few months for a modestly sized application to more than a year for a complex business system with lots of data and integrations. Splitting into batches puts modernized modules into service well before the end.
What happens to our historical data?
It is migrated to the new application after cleaning and transformation, with consistency checks and dry runs. Data that is not migrated is archived in a searchable form if regulation or the business requires it.
Can you audit our application before we decide?
Yes. The technical and functional audit is a standalone service: it gives you a status report, risks ranked by priority and costed scenarios, whether you continue with us or not.
Will our users have to relearn everything?
No. We keep the journeys that work and improve those that cause problems, involving users in the design. Training focuses on what actually changes.
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