Modernizing Legacy Applications

We update your legacy systems


When taking over and updating an existing system, it is crucial to understand the current application. This is where an analysis phase comes in. In this phase, the project's requirements and goals are identified, and the existing application is thoroughly analyzed.

Often, there is little or outdated documentation available for an existing application. Therefore, the source code of the application becomes the primary data source for the analysis.

CosmoCode employs a top-down approach for this process. The application is examined from the outside inwards. First, the application is viewed as a whole to understand its structure and architecture. Next, the individual components and modules are analyzed. The used technologies and paradigms are identified and documented.

The subsequent steps are derived from this analysis. A decision is made whether to update and modernize the existing application or if a complete rewrite is more appropriate.

Rewrite Everything?

Developers are often tempted to completely rewrite an existing application. This is understandable, as the existing application is often a patchwork of old technologies and bad code. However, a complete rewrite is not always the best solution.

An application that has evolved over years contains a wealth of knowledge that is not immediately apparent. This includes:

  • Domain knowledge and business logic
  • Bug fixes and workarounds for not always obvious issues
  • Customizations and extensions for specific customer requirements and internal processes

Moreover, users are accustomed to the existing application. They have internalized the workflows and are efficient in its use.

A careful refactoring of the existing application is often the better solution. This involves improving the code step-by-step without changing the functionality. This way, the knowledge embedded in the application is preserved, and users can continue to work efficiently.


A rewrite involves completely recreating the existing application.

  • No legacy issues
  • Full technology switch possible
  • New design and UX achievable
  • Usually a reduced feature set


Refactoring means the existing application is modernized step by step.

  • Retention of current functions and accumulated business logic
  • Can be executed during ongoing operations
  • Requires close coordination with the customer

Refactoring Timeline

Automated Testing

CosmoCode creates automated tests for the critical parts of the application. These tests ensure that the application continues to function correctly even after changes are made.

Continuous Integration/Deployment

The deployment of the application is automated. Changes are automatically tested and, if successful, deployed to staging and production environments. This prevents human errors and allows for quick and safe deployments of changes.

Dependency Updates

Frameworks used in the application, such as Django or React, as well as other libraries, are updated. This eliminates security vulnerabilities and outdated technologies.

Gradual Modernization

The application is modernized step by step. Unnecessary code is removed, and technologies are swapped out where necessary. The functionality of the affected components is reviewed and adjusted in consultation with the client.

Further Development

The application is continuously updated. New features and requirements are implemented.


Do you have an existing system that needs to be replaced or updated? We can help you understand and modernize your current application.