Why Microservices Matter: From Monoliths to Scalable Architecture

1. Introduction

Microservices is an architectural style where a large complex application is composed of many independent services and a front‑end. Each service can be deployed independently and focuses on a single business capability.

2. What is a monolithic architecture

Monolithic architecture packages all layers of an application into a single deployable unit. A typical three‑tier web app (UI, database, server) is built as one codebase; any change requires rebuilding and redeploying the whole system.

3. What is microservice architecture

Microservice architecture models the system as loosely coupled independent services built around business domains. Each service has its own database, can be written in different languages, and can be developed, tested, deployed, monitored and scaled independently.

4. Problems solved by microservices

4.1 Scalability

Monoliths can only be scaled by replicating the whole application, wasting resources. Microservices allow independent horizontal scaling of individual services.

4.2 Long delivery time

Any change in a monolith requires rebuilding and redeploying the entire system, slowing continuous delivery. With microservices only the affected service is built and deployed.

4.3 Application complexity

As a monolith grows, code becomes tangled and hard to maintain. Microservices enable teams to work on separate services, keeping codebases clean.

4.4 Lack of clear ownership

In a monolith many teams share the same codebase, creating hidden dependencies. In microservices each team owns a complete service.

4.5 Cascading failures

Failures in one part of a monolith can bring down the whole system; microservices can use circuit breakers to isolate faults.

4.6 Dev‑Ops wall

Traditional hand‑off between development and operations is reduced; the same team can build, run and maintain its service.

4.7 Technology lock‑in

Monoliths tie you to a single technology stack; microservices let each service use the most suitable language or framework.

4.8 Tooling maturity

Container platforms and cloud PaaS now provide the necessary tooling to adopt microservices at scale.

5. Summary of microservice benefits

Small, cohesive services are easy to understand and develop.

Independent deployment enables continuous delivery.

Fine‑grained horizontal and vertical scaling.

Team autonomy and clear ownership.

Improved fault tolerance.

Technology‑agnostic implementation.

Reduced cost through reuse and focused development.

5.1 Drawbacks

Increased operational complexity and cost.

Need for DevOps culture and automation.

Monitoring, testing and data consistency become harder.

Potential for many small databases and distributed transactions.

6. Hands‑on microservice example

The example provides a simple Spring Boot controller that exposes three HTTP endpoints for querying programming languages.

@ApiVersion(2)
@RequestMapping("/programLanguage/getByName")
public List<String> getByName(@RequestParam String languageName) {
    List<String> filterList = languageList.stream()
        .filter(s -> s.toLowerCase().contains(languageName.toLowerCase()))
        .collect(Collectors.toList());
    return filterList;
}

7. Microservice splitting strategy

7.1 Principles

Single responsibility, high cohesion, low coupling.

Appropriate service granularity – one service per complete business capability.

Avoid circular and bidirectional dependencies.

Align service boundaries with team structure.

7.2 Incorrect strategy

Replacing an entire legacy system with a huge new microservice set leads to long delays and high risk.

7.3 Correct strategy

Start with a small system, gain experience, then gradually expand.

Core splitting requirements: high cohesion, low coupling, minimal inter‑service calls, and avoidance of distributed transactions.

7.4 Design considerations

Consider non‑functional requirements (scalability, availability, security), complexity, team size, and existing heterogeneous technologies when defining service boundaries.

8. Migration patterns

8.1 Strangler (or “kill‑the‑old”) pattern

New functionality is built as independent services that gradually replace parts of the legacy monolith.

8.2 Rehab pattern

Problematic modules are isolated, rebuilt as services, and reintegrated, suitable for low‑change legacy systems.