What is Legacy Code? 

Legacy code is any software code that is:

  • Written in an outdated or unsupported programming language or technology
  • An old or obsolete version of a software application that is still in use

Legacy code is often kept by organizations due to the perceived cost and risk associated with updating or replacing it. It can present major challenges for businesses and development organizations.

One of the primary characteristics of legacy code is that it’s often poorly understood by current staff. The original developers may have moved on, and their knowledge and expertise went with them. Legacy code also commonly lacks comprehensive documentation or comments, making it even harder to understand and maintain.

We’ll explore some of the reasons organizations maintain legacy code, and present several strategies that can be life-savers for teams grappling with the challenges of legacy codebases.

Why Do Organizations Maintain Legacy Code? 

Continuing Business Value and Importance

Despite its challenges, legacy code remains essential to many businesses. The original software was written to solve a specific business problem, and in many cases, it continues to do so. It delivers essential functionality that the business relies on to operate efficiently. In fact, in many instances, the business may have been built around the software rather than the other way around.

Even if the software is outdated and inefficient, it’s still delivering value to the business. It may not be ideal, but it’s better than not having the software at all. Furthermore, the cost and effort of replacing the software may be prohibitively high, especially when compared to the cost of simply maintaining the existing code.

Costs and Risks Associated with Full System Replacements

When it comes to replacing legacy code, the costs can be substantial. It’s not just about the financial cost of developing new software; there’s also the time and effort required to implement the new system, train staff, and manage any teething problems that arise.

There’s always a risk that the new software won’t deliver the expected benefits or may even create new problems. This is particularly true if the original legacy code is poorly understood. If the developers don’t fully understand the existing system, they may inadvertently remove essential functionality or introduce new bugs.

Additionally, there’s the risk of business disruption. Implementing new software can be a disruptive process, and if it’s not managed effectively, it can lead to a loss of productivity and even customer dissatisfaction.

The Knowledge and Business Logic Embedded Within Legacy Systems

One of the main reasons why legacy code is so hard to replace is because of the knowledge and business logic embedded within it. The original developers built the software to solve specific business problems, and their knowledge and experience are encoded within the software itself.

This business logic is often complex and nuanced, reflecting the unique needs and challenges of the business at the time. It may not be well-documented or easily understood, but it’s essential to the operation of the business. Replacing this knowledge and business logic is not a simple task, and it’s one of the main reasons why replacing legacy code can be so challenging.

Furthermore, the business logic embedded within legacy code often reflects the history and evolution of the business. It’s a record of past decisions, successes, and failures. Replacing this code means losing this history, which can be a significant loss.

Strategies for Effectively Working with Legacy Code 

Working with legacy code can be a daunting task. However, with the right strategies in place, development teams can be successful.

1. Understanding the Codebase

The first and most crucial step in dealing with legacy code is understanding the codebase. This involves getting a sense of the overall architecture, the language used, and the techniques implemented. 

When dealing with a large and complex codebase, breaking it down into smaller, manageable components can be helpful. This approach allows for a more in-depth exploration of the code, thereby facilitating a thorough understanding of its inner workings.

2. Establish a Version Control System

The next step in effectively working with legacy code is to establish a version control system. Version control allows developers to track and manage changes to the codebase, making it easier to pinpoint when and where issues are introduced, and roll back changes if necessary.

A version control system also makes collaboration easier. With it, multiple developers can work on different parts of the codebase simultaneously without stepping on each other’s toes.

3. Create a Safety Net with Tests

Testing is a vital component of software development, and it becomes even more critical when working with legacy code. The older a system is, the more likely it is to have hidden bugs and issues that can cause problems down the line.

By creating a comprehensive suite of tests, you can catch these issues early on and address them before they become major problems. Additionally, these tests serve as a safety net, giving you the confidence to make changes to the codebase without fear of breaking anything.

4. Incremental Refactoring

Rather than trying to overhaul the entire codebase at once, I’ve found that making small, incremental changes over time can be much more manageable and effective.

Refactoring involves improving the structure of the code without changing its functionality. By doing this incrementally, you can make significant improvements to the codebase without disrupting the system’s operation.

Learn more in our detailed guide to legacy code refactoring (coming soon)

5. Documentation and Knowledge Sharing

When working with legacy code, it’s often the case that the original developers are no longer available to provide insight into the system’s inner workings. In such cases, it’s up to you to create comprehensive documentation.

Documenting the codebase, its architecture, its functionality, and any quirks it may have can be incredibly useful for future developers. Additionally, sharing this knowledge with your team can help ensure that everyone is on the same page and can contribute to the project effectively.

6. Isolate Dependencies

Legacy code often comes with a host of dependencies, which can make it difficult to understand and modify. One effective strategy for dealing with this is to isolate these dependencies.

By isolating dependencies, you can focus on understanding and modifying one component of the system at a time, rather than trying to grapple with the entire codebase at once. This approach can make the process of working with legacy code much more manageable.

7. Employ Continuous Integration

Continuous integration is a software development practice that involves integrating changes to the codebase regularly and automatically testing them to catch bugs early. When dealing with legacy code, this practice can be incredibly beneficial.

By continuously integrating changes, you can ensure that any issues introduced by modifications to the code are caught and addressed promptly.

8. Prioritize Technical Debt

Technical debt refers to the future cost of potential rework caused by choosing a quick and dirty solution now instead of using a better approach that would take longer. Legacy code often comes with a significant amount of technical debt, which can make it difficult to work with.

Prioritizing this technical debt and addressing it systematically can significantly improve the quality of the codebase and make it easier to maintain and modify in the future.

9. Stay Updated on Security

Finally, it’s essential to stay updated on security when working with legacy code. Older systems often have security vulnerabilities that can be exploited, so it’s vital to regularly review the codebase for potential issues and update it as necessary to ensure its security. 

In some cases, you will not be able to fully address security issues in legacy systems. Even so, being aware of them can help you find other strategies, such as isolating the legacy system from networks or other critical systems.

Documenting Legacy Code with Swimm

Legacy code is a critical part of many organizations’ software ecosystems, despite the challenges it presents. It continues to deliver business value and embodies essential knowledge and business logic. However, dealing with legacy code requires careful strategies to ensure its maintenance and improvement.

Understanding the codebase is the first step, followed by establishing a version control system for better management. Creating a safety net with tests helps catch hidden issues, while incremental refactoring makes the codebase more manageable. Documentation and knowledge sharing are crucial, especially when original developers are no longer available.

Swimm, with its code-coupled documentation and AI assistance for creating documentation, can be an invaluable tool in this process. It aids developers in understanding and maintaining legacy code, ultimately improving team productivity and code quality, aligning with the product’s key use cases and the needs of senior developers and development teams dealing with legacy code.

Learn more about Swimm