Defining the scope of a microservice

Defining the scope of a microservice is a critical step when designing a microservice architecture. A well-defined scope ensures that each microservice is:

  • Small and manageable

  • Loosely coupled with other services

  • Highly cohesive (does one thing well)

  • Independently deployable

Here's a practical guide to help you define the scope:

🔍 1. Start with the Business Domain (Domain-Driven Design - DDD)

Use DDD concepts to break down your application into bounded contexts. A bounded context represents a logical boundary where a particular domain model is defined and applicable.

Example:

  • For an e-commerce app, you might have:

    • User Management

    • Product Catalog

    • Order Management

    • Payment

    • Shipping

Each of these could become a separate microservice.

🎯 2. Single Responsibility Principle

Each microservice should do one thing and do it well. Avoid mixing concerns like authentication with order processing, for instance.

🔗 3. Identify Service Boundaries

Consider:

  • Ownership of data: Each service should own its own database.

  • API contracts: Define clear input/output.

  • Minimal dependencies: Avoid tight coupling with other services.

🧱 4. Think in Terms of Capabilities

Define services by capabilities rather than technical layers (e.g., avoid "UserRepositoryService"). Instead, go for "UserProfileService" or "OrderService" that handle business capabilities.

📈 5. Autonomy and Scalability

Ask:

  • Can this service be developed and deployed independently?

  • Will it need to scale separately?

⚖️ 6. Right Size It

Avoid over-engineering with too many tiny services (nano-services). A good rule of thumb: if your service logic can be owned by one small team and released independently, it's likely scoped right.

🧩 7. Define Inputs/Outputs (APIs)

Clarify:

  • What data the service needs

  • What data it provides

  • What events it listens to or emits (if event-driven)

✅ 8. Validation Checklist

Ask these questions:

  • Does the service align with a business function?

  • Can it be independently developed, deployed, and scaled?

  • Does it own its data?

  • Is the service boundary clear?

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