6 steps to addressing legacy enterprise code

Legacy code is a fact of life, but it can’t be ignored. Here are six practical steps to identify and refactor legacy code in your organization.

Legacy code is a ubiquitous challenge for software developers, especially in enterprise environments, where systems often have a long lifespan and legacy code naturally accumulates over time. This accumulation creates a particular set of challenges, but with the right strategies and techniques, it can be effectively managed and modernized.

I am proud to work for an organization that is approaching its 200-year anniversary. This rich heritage brings many benefits, and comes with great responsibility towards our customers and employees, and to our impact on society. It also means that our technology estate is an eclectic mix of cloud-native tools and apps, real-time data streams, and rapidly-evolving digital journeys; alongside mainframe data processing, and decades-old business applications. This is part of our heritage, it is a fact of life, and it is an issue that we are learning to embrace.

The simplest approach for managing legacy code is to avoid its creation in the first place, through an evergreen approach with early and continual maintenance. However, in this case we will discuss how to recover when that has not happened, exploring various approaches for managing legacy code within an enterprise.

Understanding legacy code

Legacy code is old, and often written using outdated technologies or practices, or it was developed for a business context that no longer exists. This code can be difficult to comprehend, maintain, and extend, and can often include vulnerabilities which add to the cyber threat landscape.

This sort of code exists in every organization, and it accumulates over time as new features are added, technologies and standards change, organizational structures and business models evolve, and engineers come and go.

The main challenges created by legacy code are:

Maintenance difficulty: Legacy code is often challenging to maintain. It may lack documentation, has coding standards violations, or depends on deprecated external libraries.

Risk of bugs and vulnerabilities: As legacy code ages, there is a risk of new bugs developing and of vulnerabilities becoming exploitable. This can be a significant concern, especially in security-sensitive industries.

Cost of change: Legacy code can be difficult to change, making it challenging or time-consuming to implement new features, fix bugs, or adapt to evolving business requirements.

Knowledge gaps: Over time, the engineers who originally developed the code may leave the organization. This creates knowledge gaps, making it challenging for new team members to understand and work with the legacy code. Furthermore, when developers do have enough knowledge to manage the code, they can often become key-person dependencies.

With a clear understanding of what legacy code is and the challenges it presents, let’s explore some strategies and tips for managing it effectively.

6 steps to address legacy code

The following approach is presented as steps in a process, which suggests they should be sequential. However this may not always be possible and will depend upon your context and starting point. However, the step-based approach is intentional, as there is benefit in starting by understanding your purpose and intention, and putting in-place strategies and guardrails, before starting to refactor code.

Step 1: Define and agree your intention

Why are you addressing your legacy code? What problems are you trying to address? What risks are you mitigating? Challenges will vary based on your organization and context, but defining and documenting the purpose behind your activity will guide your teams and inform your decisions in subsequent steps. Key considerations include:

• Prioritization: Work closely with stakeholders to prioritize tasks based on the scale of negative impact they are creating, and ensure that critical issues are addressed promptly.
• Cost/benefit analysis: Communicate the potential risks and benefits of changes to stakeholders, allowing them to make informed decisions. A risk-storming session can help with this.

Step 2: Invest time in documentation and code analysis

Documentation is often lacking in legacy codebases. Before making any changes, invest time in understanding the existing codebase.

• Code-base analysis: Perform a thorough analysis of the codebase to identify areas of concern, including code that needs refactoring, potential security vulnerabilities, and obsolete dependencies.
• Identify code smells: Look for code smells such as long functions, duplicated code, and excessive dependencies. These are clear indicators of areas that could benefit from refactoring.
• Code documentation: Document the code as you go, or agree to a self-documenting approach. The code’s functionality should be clear, sequence diagrams can be generated automatically, and any unusual or non-standard practices, and reasons behind specific design decisions, should be documented.
• Dependency inventory: Create an inventory of all external dependencies used by the legacy code. Check if these dependencies have newer, more secure versions available.

It is important to recognize that this is an area where AI-based tools are beginning to deliver an impactful role. There are a number of tools (Mintlify, Stenography, Theneo and others) which can automatically generate documentation based on code, and others (Codeball, Metabob, and Datadog’s Codiga), which can automate code analysis, for example.

Step 3: Identify your remediation approach

Based on your analysis, and with reference to the intentions that you defined in the first step, consider your approach to address legacy code. It can be tempting to throw old code away and buy or build something new, but this is often the most expensive, and highest-risk option.

• Technology stack evaluation: Assess whether the current technology stack is outdated and needs an upgrade. This may involve migrating to newer programming languages, frameworks, or databases.
• Consider a gradual refactoring approach: Refactoring is the process of restructuring existing code without changing its external behavior. This is generally done function-by-function, iteratively decomposing or redeveloping your application. In the context of legacy code, gradual refactoring is a powerful strategy, sometimes referred to as the Strangler Pattern. 
• Microservices and containerization: Consider breaking monolithic applications into smaller, more manageable mini- or microservices. Containerization technologies like Docker can help with this.
• Consider a façade between systems: To protect interactions between systems during your changes, an anti-corruption layer or façade can translate and preserve communication. This can be supplemented with automated tests and strong monitoring tooling.
• Cloud adoption: Explore cloud services and platforms for hosting, scaling, and managing applications. Cloud migration can improve flexibility and scalability.

Step 4: Build the right team

As with any software development, the right skills, team culture, and processes will be key to a successful delivery.

• Choose the right people: A good engineer should see themselves as a problem solver, first and foremost, and addressing legacy code is a problem to address. Often, software teams benefit from recruiting a proven problem solver with a variety of technical skills and experiences, rather than a specific technology (e.g. Java, Angular, .NET). The team will also generally require access to a functional or business subject matter expert, to understand the functionality and data flows of the software.
• Pair programming: Encourage experienced developers to work closely with those less familiar with the legacy code. Pair programming can help transfer knowledge effectively.
• Training and onboarding: Develop training programs and materials for new team members to quickly get up to speed on the legacy codebase. Consider a mentorship program where experienced developers mentor junior team members.
• Documentation standards: Implement documentation standards for new code, with a focus on self-documenting, human-readable code. As mentioned above, there is an increasing prevalence of generative AI tooling to support this.

Step 5: Prepare your safety nets

Legacy code can be fragile, and changes may introduce unforeseen issues. Effective risk management and testing are essential. 

Thankfully, it is often true that the same good practices that are used for modern code development will bring the same benefits to a legacy code context. Additionally AI-assisted tools can guide or automate the creation of test scripts.

• Testing: Test-driven development is good practice, whether for new code or when refactoring existing code. Start by creating a suite of tests for the existing code, which will serve as a safety net when you start making changes.
• Test automation: Invest in test automation to cover critical functionality and regressions. This reduces the risk of introducing new bugs during maintenance or refactoring.
• Continuous Integration/Continuous Deployment (CI/CD): Implement CI/CD pipelines to automate building, testing, and deploying code changes, reducing the manual error-prone steps.
• Rollback plans: Always have rollback plans in place in case a change leads to unforeseen issues. Being able to quickly revert to a stable state is crucial.
• Maintain a change log: Keep a detailed change log of all refactoring activities, including what was changed and why. This helps in tracking improvements and their impact.

Step 6: Refactoring

Once your strategy is agreed, and your team and safety nets are in-place, iterative code refactoring can start. 

• Isolate refactoring: Refactor small, isolated pieces of code one at a time. This minimizes the risk of introducing new bugs and makes the process more manageable.
• Code reviews: Incorporate code reviews into the refactoring process. A fresh pair of eyes can catch issues and provide valuable insights, as well as helping with knowledge sharing, training, and the avoidance of key person dependencies.
• Dependency updates: Regularly update external dependencies to their latest stable versions to fix security vulnerabilities and benefit from new features. Tools such as Dependabot, Aikido, and GreenKeeper can help to automate this process.
• Transparent communication: Keep stakeholders informed about the progress of code management, the reasons behind changes, and the potential impact on business operations.

Final thoughts     

Legacy code is a challenge that every enterprise software development team must face. However, with the right strategies and techniques, it is possible to manage, refactor, and modernize legacy code effectively. The key is to approach the process with a clear strategy, open communication, and a commitment to continuous improvement.

In the ever-evolving world of software development, the ability to manage legacy code is a skill that every enterprise should cultivate. With careful planning and a commitment to best practices, along with a rapidly-evolving, AI-enabled toolset, even the most challenging legacy codebases can be tamed and brought into alignment with modern development standards, and then maintained effectively to avoid the issue recurring.

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