How to Handle Duplicate Code: Comparing the Options

Duplicate code is a common issue in software development, often referred to as code duplication or "DRY" (Don't Repeat Yourself) violations. While it might seem harmless at first, duplicate code can lead to maintenance headaches, inconsistencies, and increased technical debt as your project grows. When faced with duplicate code, developers have several options: they can either duplicate the code, create a shared library, make a service that encapsulates the shared logic, or use a sidecar pattern. Each approach has its pros and cons, and the best choice depends on the specific context of the project.

In this blog post, we’ll explore these four strategies, comparing their benefits and trade-offs to help you make an informed decision.

1. Just Duplicate the Code

The simplest approach to handling code duplication is, surprisingly, to just duplicate the code. This means copying and pasting the code across different parts of the application, resulting in multiple instances of the same logic.

Advantages

• Simplicity: There’s no need to refactor or introduce new dependencies. Developers can get things done quickly without worrying about breaking other parts of the system.
• Decoupling: Each instance of the duplicated code is independent, meaning changes in one place don’t affect others. This can be useful when different parts of the system evolve independently over time.
• Ease of Deployment: No additional services or shared libraries are required, which keeps the deployment process simple.

Disadvantages

• Maintenance Nightmare: As the code evolves, any bug fixes or feature updates must be made in multiple places, increasing the risk of inconsistencies and errors.
• Technical Debt: Over time, duplicate code can lead to significant technical debt, making it harder to maintain and extend the codebase.
• Code Bloat: The overall size of the codebase increases, which can impact readability and make the project more challenging to navigate.

When to Use

• Short-term Projects: If the project is short-lived or unlikely to change, duplicating code might be acceptable.
• Isolated Duplication: If the code is unlikely to change or be reused, and the duplication is minimal, this approach might be sufficient.

2. Make a Shared Library

A more common and sustainable approach to handling duplicate code is to create a shared library. This involves extracting the duplicate code into a separate module or library that can be imported and used across multiple parts of the application.

Advantages

• Reusability: The shared library can be used by multiple components or even across different projects, reducing redundancy and ensuring consistency.
• Centralized Maintenance: Any changes or bug fixes to the shared logic only need to be made in one place, simplifying maintenance.
• Versioning: Libraries can be versioned, allowing different parts of the system to upgrade at their own pace, reducing the risk of breaking changes.

Disadvantages

• Tight Coupling: Applications that depend on the shared library become tightly coupled to it, which can limit flexibility.
• Dependency Management: Managing dependencies and versions across different projects can become complex, especially if the shared library evolves rapidly.
• Deployment Overhead: Updating the shared library often requires redeploying all dependent services or applications, which can be cumbersome.

When to Use

• Cross-Cutting Concerns: If the duplicate code is related to cross-cutting concerns like logging, authentication, or utility functions, a shared library is an excellent choice.
• Large-Scale Systems: In large-scale systems where multiple services or applications need to share common logic, a shared library promotes consistency and reduces redundancy.

3. Make a Service with the Shared Code

Another approach is to encapsulate the duplicate logic in a separate service that other services or applications can call via APIs. This is common in microservices architectures, where functionality is broken down into discrete, reusable services.

Advantages

• Loose Coupling: Services interact through well-defined APIs, reducing coupling and making it easier to evolve and deploy them independently.
• Scalability: The service can be scaled independently based on demand, which is particularly useful for resource-intensive operations.
• Centralized Logic: The shared logic is centralized, making it easier to update and maintain. Clients only need to call the service without worrying about implementation details.

Disadvantages

• Network Latency: Calling a separate service introduces network overhead, which can affect performance, especially for high-frequency operations.
• Operational Complexity: Running and maintaining an additional service requires more infrastructure, monitoring, and management.
• Increased Failure Points: The service introduces another point of failure. If it goes down, all dependent services are affected.

When to Use

• Microservices Architectures: In a microservices architecture, where services are designed to be loosely coupled and independently deployable, creating a separate service for shared logic is often the best choice.
• Heavy or Specialized Logic: If the shared code is computationally heavy or highly specialized, encapsulating it in its own service allows for better scaling and optimization.

4. Use a Sidecar Pattern

The sidecar pattern involves running the shared code as a separate, but tightly coupled, process alongside the main application. The sidecar handles specific functionalities, such as logging, monitoring, or authentication, that can be reused by multiple services.

Advantages

• Decoupling from Application Logic: The main application doesn’t need to implement the shared logic directly. Instead, it delegates these tasks to the sidecar.
• Isolation: The sidecar runs as a separate process, which can be managed, deployed, and scaled independently, without interfering with the main application.
• Reusability Across Services: Multiple services can share the same sidecar, ensuring consistent behavior across the system.

Disadvantages

• Increased Complexity: Managing and orchestrating sidecars can add complexity to the deployment and operational processes.
• Resource Overhead: Running a sidecar alongside each instance of an application consumes additional resources, which can be significant in large-scale deployments.
• Communication Overhead: The main application and the sidecar need to communicate, which, although often local, still adds some overhead.

When to Use

• Service Meshes: The sidecar pattern is popular in service mesh architectures, where concerns like observability, security, and traffic management are handled by sidecars.
• Cross-Cutting Concerns with Tight Coupling: If the shared logic is tightly coupled with the application’s runtime but needs to be isolated, a sidecar can be an effective solution.

Comparing the Approaches

Conclusion

Handling duplicate code is a critical decision in software development, and the approach you choose should align with your project’s architecture, team expertise, and long-term goals. While duplicating code may be the quickest solution in the short term, it often leads to technical debt and maintenance challenges down the road. Shared libraries and services provide more sustainable solutions, with shared libraries being suitable for reusable logic and services excelling in distributed systems. The sidecar pattern, although more complex, offers a powerful way to manage cross-cutting concerns in service meshes.

Ultimately, there is no one-size-fits-all solution. Each approach has its own trade-offs, and the right choice depends on your specific use case. By understanding the advantages and disadvantages of each option, you can make a more informed decision that balances simplicity, scalability, and maintainability in your software architecture.