Shared Libraries- do we still need them?

You're absolutely right to question the potential drawbacks of a monolithic shared library. While it solves the immediate duplication problem, it can introduce new challenges if not managed carefully. Here's a deeper dive into best practices and considerations:

The Pitfalls of a Monolithic Shared Library:

• Tight Coupling:

  • A large, shared library can create tight coupling between microservices.

  • Changes in the shared library can have unintended consequences for other services.

• Version Conflicts:

  • Different microservices may require different versions of the shared library.

  • Managing these versions can become complex.

• Deployment Dependencies:

  • Changes in the shared library may require redeploying multiple microservices.

  • This can increase deployment complexity and downtime.

• Increased Build Times:

  • Large shared libraries can increase the build time of the microservices.

Best Practices for Shared Libraries (and Alternatives):

1. Bounded Contexts and Focused Libraries:

   • Instead of one giant "common" library, break it down into smaller, more focused libraries aligned with bounded contexts.

   • For example, you might have separate libraries for:

     • shared-security

     • shared-data-access

     • shared-api-contracts

     • shared-utilities

   • This reduces coupling and makes it easier to manage dependencies.

2. Semantic Versioning:

   • Use semantic versioning (e.g., 2.1.3) to clearly indicate breaking changes, new features, and bug fixes.

   • This helps microservices manage dependencies and avoid unexpected issues.

3. API Contracts (OpenAPI/Swagger):

   • Prioritize API-first design and use OpenAPI (Swagger) to define API contracts.

   • Generate client stubs from these contracts.

   • This minimizes the need for shared code related to API communication.

4. Avoid Shared Domain Models:

   • Resist the temptation to share domain models between microservices.

   • Each microservice should have its own domain model, tailored to its specific needs.

   • Use DTOs (Data Transfer Objects) for communication between services.

5. Consumer-Driven Contracts:

   • Use consumer-driven contracts to define the interactions between microservices.

   • This allows consumers to specify their requirements, ensuring that providers don't introduce breaking changes.

6. Version Compatibility Testing:

   • Implement thorough version compatibility testing to ensure that microservices can work with different versions of the shared libraries.

   • Automate tests that verify the interaction between the microservices and the shared libraries.

7. Consider Code Generation:

   • For common, repetitive code, consider using code generation tools. This can reduce the need for shared libraries in some cases.

8. Git Submodules/Subtrees (Use with Caution):

   • While technically an option, Git submodules or subtrees for shared code can add complexity to version control and build processes. Use these with extreme care, and only when you have a very specific need.

9. Build and Publish Frequently:

   • Publish your shared libraries to your artifact repository frequently. This allows microservices to consume the latest changes as needed.

10. Documentation:

    • Document the shared libraries thoroughly. This helps developers understand how to use them and avoid potential issues.

In Summary:

• Shared libraries are a valuable tool, but they must be used judiciously.

• Prioritize loose coupling, clear API contracts, and well-defined boundaries.

• Favor smaller, focused libraries over large, monolithic ones.

• Automate testing to ensure version compatibility.

• Consider code generation and consumer driven contracts.

By following these best practices, you can leverage shared libraries effectively without introducing unnecessary complexity into your microservice architecture.