6 steps to addressing legacy enterprise code

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• Technology stack evaluation: Assess whether the current technology stack is outdated and needs an upgrade.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

• 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.

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

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.