Everything You Need to Know About Legacy Code

One common mindset of developers is to treat every Legacy code as bad. However, in reality, no developer intends to develop an application based on codes that are complex to compile, debug or migrate to a new platform.


Everything You Need to Know About Legacy Code
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For an organization that is through several years of dealing with technology, the term Legacy Code isn’t alien. More often, the term itself is treated with a negative connotation for something which is useless or unworkable. However, the fact remains completely different from the widespread perception, considering there are several approaches to deal with such inherited logics. Let's discuss this in detail. 

What is a Legacy Code?

The term Legacy Code usually refers to an application source code that has reached or crossed an end of the support cycle. Often, this may also imply that parts or whole of the application's supported technology stack are either too complex, outdated, or irrelevant to maintain when compared with modern platforms. As applications rely on specific languages, libraries, compilers, and operating architecture, a Legacy Code relates to either of such components to be superseded by modern technologies. Besides these, developers often treat a source code as Legacy which is complex to debug or change. 

Challenges in Maintaining a Legacy Code

One common mindset of developers is to treat every Legacy code as bad. However, in reality, no developer intends to develop an application based on codes that are complex to compile, debug or migrate to a new platform. To update/change an older version of the software, an organization must spend efforts to understand the older code's basic functionality, and then develop a new and effective codebase for the next sprint of release. Here are some of the most common challenges that organizations face while trying to maintain a legacy code: 

Emerging Platform Support

Due to advancements in technologies, it is of utmost importance for organizations to consistently adopt emerging technologies that enable operational excellence. Quite more than often, legacy codes act as roadblocks to a seamless migration to newer frameworks due to their lack of efficiency or compatibility. An example scenario to this is an organization that is migrating from an on-prem to cloud framework. In such cases, certain legacy application codes may not be compatible or supported by the cloud service provider. Beyond immediate compatibility issues, this also acts as a permanent roadblock to embracing efficient models such as DevOps that enable automation across all layers of a workflow. 

Adding New Features

Adding new features and functionalities to an inherited code is not only complex but may result in an enormous amount of effort to make all elements work as intended. Doing so requires not only the legacy code to be updated, but also related libraries, configuration files, and platform components need to be updated to maintain compatibility. Particularly for applications that follow a monolithic architecture, where every component is dependent on another, updating a single module may pose catastrophic effects by collapsing parts or whole of the application.  


Possibly one of the biggest impacts of a legacy code is its lack of updated documentation, including an up-to-date bug tracker. As a result, legacy codes are considered less stable and more fragile in the current or future sprints of an application. Not only this, lack of efficient debugging often leads to exposing vulnerable areas of the application that are susceptible to security attack vectors. A common reason for this may also relate to the fact that the current set of developers do not understand the written module’s usability, thereby introducing new bugs while migrating to a new platform or implementing new features. 

Best Practices To Fix Legacy Code

Fixing a Legacy Code is difficult, but it isn't impossible. Instead of being judgemental about the code past developers, it is best to focus more on finding out errors and compatibility issues to make the codebase clean. 

Here are a few approaches to improve or manage a Legacy Code: 

Segregate in Multiple Smaller Modules

The first step to begin working with a Legacy Code is by starting to divide it into modules and fix those progressively for compatibility, bugs, or security issues. Breaking a code into smaller modules not only helps fix issues but also enables easier identification of dependencies and cross-compatibility. Doing so requires deleting lines of dead codes that are no longer relevant as well as rewriting those which should be updated. 


Debugging a Legacy Code is one of the critical determining factors to ensure its usability. Fundamentally, Unit Testing and Characterization of Tests are considered the best approaches to test such a code. As inherited codes are complex to debug, such practices when used with the right tools (such as Static Analyzer) often act as the first step to analyze, identify, and write these into a simple and clean code. This also paves the way to refactoring a legacy code by making changes to the existing codebase.

Centralizing Decision

As a best practice, it is always recommended to follow a centralized approach of maintaining, fixing, or rewriting inherited code. This not only enables efficient collaboration and decision-making strategies to complete a project on time but also allows to maintain a centralized repository of bug tracker and version control

Rewriting & Refactoring

It must be noted that every approach to fix a legacy code eventually correlates to rewriting or refactoring it for current and future platform adaptability. This includes reviewing documentation, rewriting the code, and/or refactoring module-level functionalities of the code that meets current platform requirements as well as allowing future interoperability.  

Retaining a Legacy Code

Not all Legacy Codes are poorly written. The code that is inherited from an older version of the software can be retained unless there are genuine reasons to change. The key to maintain and manage a legacy code is to undertake a thorough discovery phase that helps identify potential challenges and dependencies on an obsolete platform. By the end of the discovery, there are always arguments whether to rewrite the code entirely or refactor it gradually. 

Rewriting a Legacy Code

Theoretically, rewriting a legacy code requires a top-down approach to rewrite the code in its entirety. Rewriting is particularly chosen for applications where the legacy code has too many challenges, poorly documented with no earlier developers around, or in cases of a major migration of architectural frameworks. Such scenarios call for the need to rewrite the full code to avoid future complexities. However, due to the sheer amount of effort that is required to do so, rewriting is often considered as the last bet when there are no possible moves left.

Refactoring a Legacy Code

On the other hand, refactoring allows a gradual approach to update in parts dead or error lines of code from the application codebase. This turns out to be a preferred choice where existing issues on certain parts of the code are already identified, and there is evident clarity on what needs to be changed. Refactoring is also the preferred technique to clean a legacy code that is too complex, poorly written, or has too many errors with identified root causes.  However, in the absence of the right skill sets and a thorough due-diligence, refactoring a legacy code may turn out to be risky with a high possibility of breaking current functionalities of even the steady modules. The idea behind refactoring a Legacy Code is to make the code simpler and easy to understand.

Final Words

Working with legacy codes isn't always straightforward and requires a positive mindset to solve problems. While there are challenges to deal with a legacy code, with the right practices, tools, and robust analysis, dealing with legacy codes isn’t always a liability. Fixing inherited codes also requires the right combination of methodologies and skilled experts. At Enkonix, we take pride in claiming that we have helped multiple clients to analyze, refactor or rewrite legacy applications. By providing a comprehensive consultancy across multiple technology segments, we help organizations achieve a strong foundation for adopting emerging technologies. Contact us today to know more!

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