Refactoring Applications for the Cloud: Best Practices

Application modernization is a critical part of digital evolution, letting you take advantage of cutting-edge cloud infrastructure to improve performance, reduce costs, and increase reliability, availability, and flexibility. Because each application is different, there is no one-size-fits-all approach.

Strategies for application modernization fall into seven categories: Rehost, Replatform, Refactor, Rearchitect. Rebuild, and Replace. In this blog, we take a deeper dive into the refactoring approach — what it is and how to go about doing it.

What Is Refactoring?

Refactoring involves strategically rewriting certain functions within your application instead of rewriting the entire application. It allows you to improve large sections of your application with laser-like precision. For example, you can use refactoring to decompose a monolithic application into microservices or refactor code to be more concise and readable.

Refactoring is one of the easiest ways to modernize because you can make small, incremental changes to improve the application over time instead of undertaking a complete rewrite with new, untested code that could lead to unknown consequences. Refactoring improves the code structure and design, making it easier to read and simplifying maintenance. This approach minimizes widespread changes, thereby reducing risk. Improved code readability allows for better understanding and confidence when adding new features, enhancing function composition, and increasing developer velocity. Consequently, the code becomes less brittle, making it easier and faster to fix issues when they arise.

How to Refactor

You can use the following steps as a guideline for planning and carrying out a refactoring project.

Step 0 is actually to ensure you have unit tests. You must have unit tests to ensure your refactoring hasn't broken things. Then follow these steps:

1. Assess the Current State

Start by understanding your existing code. To analyze what the code is doing, you can use AI tools such as Amazon Q Developer (formerly CodeWhisperer) and Anthropic’s Claude in Amazon Bedrock.

Once you have established a baseline understanding, you can assess technical debt accrued from previous shortcuts or quick fixes, which may require extensive refactoring. For example, you can do performance testing to see if you are running on the right EC2 instance type. Overall, you want to determine the most problematic areas so you can target the hotspots (e.g., performance, defects, resiliency).

2. Set Goals

The next step is to ascertain the business requirements and user needs for the application. It’s essential to collaborate with your technology experts, power users, and cross-business teams to capture requests and requirements, such as:

• Better performance
• Less technical debt
• Lower costs
• Less complex management
• More resiliency
• Better ability to ride out temporary failures or traffic spikes
• More metrics for observability

With these goals established, define where each one falls on a continuum from critical to not applicable. Use your findings to prioritize refactoring tasks based on impact and urgency. Establish clear metrics to define the effectiveness of the refactoring process, such as code quality scores, bug counts, performance benchmarks, and user feedback.

3. Plan the Refactoring Process

Use the priority list from Step 2 to determine which application components will be refactored. You should do a detailed discovery of each component to note where the interlaced dependencies are and how they will be coordinated for development and deployment. Then, determine the impact on data sources, integrations, logging, alerting, and the user base.

Based on the components involved, you can then set the project scope and objectives. Explain what’s included and what will be done, breaking down the process into manageable tasks. Name the relevant technologies, platforms, frameworks, languages, and logging. Define risks, along with plans for mitigation, acceptance, avoidance, etc. List the deliverables and milestones in phases with timelines. Allocate resources such as coders, testers, usability, and project management.

With this plan in place, estimate your final budget needs and gain approval. Be sure to communicate with other stakeholders and team members to inform them of any impact the refactoring process may have on their application experience.

4. Apply the Right Refactoring Techniques

There are a variety of techniques and approaches you can employ in a refactoring project, depending on the specific needs of your environment:

• Extract method: Reorganize sections of code into smaller and more granular methods to make each method more readable and reusable.
• Rename variables: Change the identifiers for code symbols (e.g., fields, local variables, methods, namespaces, properties, and types) to make code more understandable.
• Replace conditionals with polymorphism: Replace if-else and switch statements with a more flexible and extensible object-oriented design.
• Replace direct invocations with message passing for a more flexible and maintainable design.
• Replace magic numbers with named constants to make the code easier to understand and less error-prone.
• Add logging at function boundaries to provide visibility into the execution flow of the application.
• Let AWS do the undifferentiated heavy lifting for you: Replace bespoke code with calls to managed services to offload non-core or repetitive tasks. AWS has a variety of managed services, such as Amazon SNS, Amazon CloudWatch, Amazon SQS, and Amazon EKS, that can reduce the amount of code you have to write or maintain yourself.

5. Follow Best Practices

Begin with small chunks of code to minimize the risk of errors. Run comprehensive unit tests (remember Step 0) and integration tests before and after each refactoring to ensure the application's behavior remains intact. Follow established design patterns, such as collaborating with testers, automating the build and deploy process, refactoring in small steps, troubleshooting and debugging separately, and prioritizing code deduplication to improve maintainability and scalability. 

Use version control systems to collaborate, track changes, and make it easier to revert if needed. Be sure to document the reasons behind each change to capture the context for future developers. Monitor the performance impact of each change to guard against introducing new issues.

6. Address Challenges

Be aware that legacy applications will have outdated or poorly structured code that lacks documentation and may have hidden dependencies that can complicate refactoring efforts and require additional adjustments. Allocate enough time for thorough refactoring to avoid rushed or incomplete changes.

Anticipate some resistance to change from team members and be ready to address it with a combination of communication, collaboration, training, and support. Avoid the temptation to give in to scope creep, addressing unrelated issues, or implementing new features, which can add to timelines and complexity.

7. Monitor and Iterate

Use monitoring tools to identify any performance bottlenecks and address them iteratively. A few examples include:

• Amazon CloudWatch: Monitor applications, respond to performance changes, optimize resource use, and gain insights into operational health
• AWS CloudTrail: Audit, monitor, and troubleshoot by tracking user activity and API usage
• AWS X-Ray: Gain visibility and traceability of requests as they traverse through your application 

Gather feedback from stakeholders, end users, developers, and other sources and systems to assess the impact of refactoring based on your initial success criteria. Use feedback gathered from monitoring, testing, and user reports to prioritize and plan further iterations of refactoring. It’s also important to conduct regular code reviews to identify areas for improvement.