Shared Library vs Shared Service: A Better Alternative for Code Reuse

The primary alternative to using a Shared Library is using a Shared Service.

Instead of reusing code through a shared library inside a Laravel project, you can move shared logic into an independent service, and let other services or modules consume it via an API or client.

This approach shifts reuse from code-level sharing to behavior-level sharing.

A Practical Example

Imagine you have multiple services that deal with customers, such as:

• Orders Service
• Notifications Service

All of them need to check the customer’s balance before performing certain operations.

The Shared Library Approach

You could:

• Create a shared library
• Import it into every service
• Re-deploy all services whenever the logic changes

This creates tight coupling and coordinated deployments.

The Shared Service Approach

Instead, you create a dedicated CustomerBalanceService.

Each service:

• Calls CustomerBalanceService when it needs to validate customer balance
• Does not own the balance calculation logic

Now, if you:

• Change the calculation rules
• Add new validation constraints

Only CustomerBalanceService needs to be modified and deployed. All consuming services automatically benefit from the change.

Composition Over Inheritance

The key idea here is that reuse happens through composition, not inheritance.

• Services use CustomerBalanceService
• They do not extend or inherit from its classes

This provides:

• Greater flexibility
• Better service autonomy
• Looser coupling between components

Each service remains independent, with a clear contract between them.

Architectural Trade-offs

Like any architectural decision, shared services come with trade-offs.

1. Change Risk

Any change in the shared service can impact all dependent services. This requires:

• Strong versioning
• Backward compatibility
• Careful contract design

2. Performance

Calling a shared service usually means:

• A network call
• Higher latency compared to a local library call

This must be evaluated carefully, especially in high-throughput paths.

3. Fault Tolerance

If the shared service goes down:

• All dependent services may be affected

This makes the following essential parts of the design:

• Circuit breakers
• Retries
• Caching
• Fallback strategies

Final Thought

Shared services promote:

• Better separation of concerns
• Centralized business rules
• Independent deployments

But they also introduce:

• Runtime dependencies
• Operational complexity

Choose shared services when business logic truly belongs to a single authority, and be intentional about the trade-offs.

Good architecture isn’t about eliminating problems — it’s about choosing which problems you’re willing to manage.