Breaking the Monolith in 2025: Microservices vs Modular Monolith

Why This Matters?

In 2025, businesses need scalable, resilient, and fast-to-market applications. Traditional monolithic architectures often slow down innovation, making releases cumbersome and introducing risks of system-wide failures.
The rise of Microservices and the more balanced approach of a Modular Monolith present two strong options for modern architecture.
But which one fits your needs? Let’s break it down in simple terms.

Let’s get to it

Imagine you run an e-commerce app. In a monolithic system, the product catalog, cart, payments, and delivery tracking are all part of one giant codebase. If you need to update the payment feature, you must test and deploy the entire application.
This slows you down and makes even small changes risky.

Enter Microservices: you split that big app into small, independent services – one for products, one for payments, one for delivery. Each service runs independently and can be deployed without impacting the others.
Sounds amazing, right? But it comes with complexity – managing many small services is not easy.

Now, a Modular Monolith is like a well-organized house. Everything is in the same building (same codebase), but each room (module) has clear boundaries and rules.
You keep the simplicity of deployment while avoiding the chaos of a “big ball of mud.”

Real-world analogy:
– Monolith = A single large warehouse where all goods are kept together. Easy to manage initially, but hard to scale.
– Microservices = Multiple warehouses across cities – super scalable but needs logistics and coordination.
– Modular Monolith = One big warehouse divided into well-marked sections. Easier to manage and somewhat scalable.

How it helps

Microservices vs Modular Monolith: A Practical Comparison

Aspect	Microservices	Modular Monolith
Deployment	Independent deployments per service	Single deployment for the whole app
Scalability	Excellent (scale individual services)	Limited to horizontal scaling of the entire app
Complexity	High (network calls, service discovery, CI/CD)	Moderate (still one codebase)
Performance	Network overhead between services	Faster (in-process calls)
Cost	Higher (infra, DevOps, monitoring)	Lower (simpler infra)

Pros of Microservices

Independent deployments and faster scaling
Better fault isolation – one service failing doesn’t crash the entire app
Tech flexibility (use different languages per service)

Cons of Microservices

Complex to implement (requires DevOps maturity)
Harder debugging and monitoring (distributed tracing needed)
Network latency and higher infra costs

Pros of Modular Monolith

Simple to deploy and maintain
Fewer infrastructure requirements
Better performance due to in-process communication

Cons of Modular Monolith

Still a single point of failure
Scaling is less granular (entire app scales together)
Requires strict discipline to avoid module coupling

Microservices Code Example (Spring Boot)

Below is a basic structure of a Spring Boot Microservice for a Product service:


// ProductServiceApplication.java
@SpringBootApplication
@EnableEurekaClient // For service discovery
public class ProductServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(ProductServiceApplication.class, args);
    }
}

// ProductController.java
@RestController
@RequestMapping("/products")
public class ProductController {
    @GetMapping
    public List<String> getProducts() {
        return List.of("Laptop", "Phone", "Tablet");
    }
}

// application.yml
server:
  port: 8081
spring:
  application:
    name: product-service
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/

This example registers the service with a Eureka Server for discovery, a common pattern in microservices architecture.

Modular Monolith Code Example (Spring Boot)

A Modular Monolith uses packages/modules to enforce boundaries. Here’s an example structure:


// Module: product
package com.example.app.product;

@Service
public class ProductService {
    public List<String> getProducts() {
        return List.of("Laptop", "Phone");
    }
}

// Module: order
package com.example.app.order;

@Service
public class OrderService {
    private final ProductService productService;

    public OrderService(ProductService productService) {
        this.productService = productService;
    }

    public String placeOrder() {
        return "Order placed for: " + productService.getProducts().get(0);
    }
}

Key difference: Both modules are in the same codebase, but structured with clear boundaries and interfaces. You can use Java 17 modules or tools like ArchUnit to enforce modular rules.

In essence

Monoliths are simple but become a bottleneck at scale.
Microservices offer agility and scalability but bring operational complexity.
Modular Monolith is the sweet spot for many teams in 2025 – structured, modular, and less costly.
Start simple, evolve when needed: Don’t jump into microservices without a clear need and team capability.

Muses of a Reticent Techie

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