# Legacy application refactoring: 6-step methodology

How to modernize an aging application without risking service continuity? Our proven methodology.

## The legacy application challenge

Your business application is 10 years old, it still works but is becoming difficult to maintain. A refactoring is necessary, but how to proceed without risk?

## Step 1: Audit and mapping

Document the existing system: architecture, dependencies, technical debt, data flows. Without this clear vision, you're navigating blind.

## Step 2: Define the target

What modern architecture to aim for? Microservices, modular monolith, serverless? The choice depends on your constraints and objectives.

## Step 3: Migration strategy

Three possible approaches:

- **Big bang**: risky but fast
- **Strangler pattern**: progressive and safe
- **Parallel reconstruction**: expensive but risk-free

## Step 4: Quick wins

Identify the most problematic modules to refactor first. Prove value quickly.

## Step 5: Iterative execution

Proceed in sprints with regular deliveries. Each iteration brings value and reduces risk.

## Step 6: Switchover and decommissioning

Migrate users progressively. Keep the old system running in parallel until validated.

## Conclusion

A successful refactoring requires method and patience. Generally allow **12 to 24 months** for a critical application.