Mastering Microservice Design: 5 Essential Architectural Constraints

Microservices are a new software architecture and delivery model, where an application consists of several small runtime services.

Traditional software delivery builds, integrates, and tests the entire application as a whole, requiring a full test cycle even for tiny changes.

Microservice‑based development treats each module as an independent runtime service with a well‑defined API, allowing faster delivery of small incremental changes.

Adopting microservices requires careful consideration of several factors:

Microservice practices must be built on proven software design, architecture, and DevOps patterns.

They demand expertise in distributed development and architecture; without proper tools, a premature shift can become a nightmare.

The remainder of this article defines five architectural constraints for microservice styles.

To qualify as a microservice, a service must be:

Scalable

Elastic

Composable

Minimal unit

Complete

Microservice Design Constraint 1: Scalability

Microservices must be able to scale independently, both up and down, alongside other services in the same application.

This constraint allows fine‑tuning performance, availability, and resource usage based on load or other factors, typically achieved by running multiple stateless instances with service naming, registration, discovery, routing, and load balancing mechanisms.

Microservice Design Constraint 2: Elasticity

Failure of a microservice should not affect other services in the application.

Elasticity (or resilience) means that when a single service instance fails, the impact on the overall application is minimal, and users can continue using unaffected parts of the system.

Microservices are loosely coupled, context‑bounded services that isolate failures to a single functional area.

Microservice Design Constraint 3: Composability

Microservices must provide a uniform interface and support service composition.

The API of a microservice carries a distinct identifier and follows REST’s uniform interface constraints, enabling aggregation, linking, caching, proxying, and gateway patterns.

Microservices should contain highly cohesive entities.

High cohesion means that a module’s objects and functions focus on a single responsibility, making the software easier to maintain.

Each microservice should implement a single business function with all its components highly cohesive, aligning with the single‑responsibility principle.

Microservice Design Constraint 5: Completeness

Microservices must guarantee functional completeness.

As Bjarne Stroustrup said, good software is “as small as possible but complete.” A microservice provides full functionality with minimal dependencies on other services, enabling independent versioning and upgrades.

Without this, managing service versions and upgrades becomes impossible.

Conclusion

Designing microservice applications requires modular design, service‑oriented principles, and adherence to proven patterns and best practices.

The five constraints described help practitioners follow microservice architecture rules and realize its core characteristics.

For example, the first constraint’s elasticity is achieved by separating data and application layers into stateless services.

We have helped a team build a solution that follows these rules, enabling easy deployment and operation of microservice applications.

Container‑based microservice applications will power the next generation of software innovation.

If you are using or interested in microservices, feel free to leave a comment below.