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Microservices have become a widely adopted paradigm thanks to their flexibility, scalability and the way they ease the maintenance of complex applications. But when should a feature be considered a new microservice? This article covers the guidelines for making that decision and the advantages the architecture offers.

When should a feature become its own microservice? Six guidelines for deciding, the advantages of the architecture, and the complexity it brings.

What Are Microservices?

Microservices are an architectural style in which an application is split into small, independent services, each responsible for a specific capability of the system. They usually communicate with each other through APIs, and they can be developed, deployed and scaled independently.

Guidelines for Identifying a New Microservice

Not every feature in a system justifies becoming a microservice. These are the main guidelines to consider.

1. Functional Autonomy

If a feature can operate independently, without being tightly coupled to other parts of the system, it's a good candidate.

Example: an authentication service or a payment management service.

2. Independent Scalability

If a feature has scaling requirements that differ from the rest of the application, that can justify a separate service.

Example: an image processing service that needs a lot of compute capacity.

3. Reusability

If a feature is used by several systems or applications, turning it into a microservice encourages reuse and reduces duplication.

Example: an email notification service.

4. Independent Lifecycle

If a feature needs a development and deployment cycle different from the rest of the system, it should be a microservice.

Example: a machine-learning recommendation service that needs frequent updates.

5. Clear Business Domains

Following Domain-Driven Design (DDD), features that represent a well-defined business subdomain are ideal candidates.

Example: an inventory management service in an e-commerce system.

6. Size and Complexity

A microservice should be small enough to focus on one specific task, but large enough not to fragment the system excessively. If a feature is trivial or heavily dependent on others, it probably doesn't justify becoming a microservice.

Advantages of a Microservices Architecture

1. Scalability: you can scale only the parts of the system that need it, instead of the whole application.
2. Technology flexibility: each microservice can use the language or technology that best fits its job.
3. Independent development and deployment: teams can work on different microservices at the same time, speeding up development and continuous delivery.
4. Resilience: because services are decoupled, the failure of one doesn't necessarily bring down the rest of the system.
5. Reusability: well-designed microservices can be reused across projects and contexts.
6. Easier maintenance and updates: it's simpler to update or fix a bug in one microservice without affecting the whole application.

Final Considerations

Despite its advantages, a microservices architecture adds complexity to running the system: advanced monitoring, versioning, and managing communication between services. That's why it's essential to analyze carefully before deciding to split a feature into a new microservice.

In short, adopting microservices can change how applications are designed, built and maintained, allowing a stronger focus on quality, scalability and agility, as long as the decision to split is made deliberately. If you're still weighing the trade-offs, Modular Monolith or Microservices? A Framework for Deciding Without Dogma goes deeper into that decision.