Decomposing Monoliths to Microservices
Learn strategies for breaking down large monolithic applications into smaller, independent services.
Decomposing Monoliths to Microservices is a free Spring Boot 4 Microservices & REST APIs lesson on CoddyKit — lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Boot 4 Microservices & REST APIs learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What is a Monolith?
Before we break things apart, let's understand what a monolithic application is.
A monolith is a single, large application where all components—like the user interface, business logic, and data access layers—are tightly coupled within one codebase.
Think of it as a single, giant block of software.
Monoliths: The Growing Pains
While easy to start, monoliths often face challenges as they grow:
- Slow Development: Large codebase means longer build times and complex merges.
- Scaling Issues: To scale one part, you must scale the entire application.
- Technology Lock-in: Hard to introduce new technologies without rewriting the whole system.
- Deployment Risk: A small change requires redeploying the entire application, increasing risk.
Enter Microservices
Microservices are an architectural style where an application is built as a collection of small, independent services.
- Each service focuses on a single business capability.
- They run in their own processes.
- They communicate with each other using lightweight mechanisms, often HTTP APIs.
This approach aims to solve the problems faced by large monoliths.
Decomposition Strategy: Business Capabilities
One primary way to break down a monolith is by business capabilities.
Identify the core business domains or functions within your application (e.g., 'Order Management', 'User Accounts', 'Product Catalog'). Each of these becomes an independent microservice.
This means focusing on 'what it does' rather than 'how it's built'.
Business Capability Example
Here's a conceptual Java example showing how different business capabilities might exist as separate logical components, even if in a single program for illustration.
public class OrderService {
public String processOrder(String orderId) {
return "Order " + orderId + " processed.";
}
}
public class UserService {
public String getUserDetails(String userId) {
return "Details for user " + userId + ".";
}
}
public class Main {
public static void main(String[] args) {
OrderService orderService = new OrderService();
UserService userService = new UserService();
System.out.println(orderService.processOrder("ORD123"));
System.out.println(userService.getUserDetails("alice"));
}
}Decomposition Strategy: Bounded Contexts
Another powerful concept from Domain-Driven Design (DDD) is Bounded Contexts.
A bounded context defines a clear boundary within which a particular model (like 'Product' or 'Customer') is consistent and unambiguous. The same term might mean different things in different contexts.
Using bounded contexts helps you define clear, logical boundaries for your microservices, reducing confusion.
Decomposition Strategy: Strangler Fig Pattern
The Strangler Fig Pattern is a safe, incremental approach to migrating from a monolith to microservices.
It involves gradually replacing specific functionalities of the old monolith with new microservices. A 'facade' or 'proxy' then intercepts incoming requests, routing them to either the new service or the old monolith.
Over time, the new services 'strangle' the old monolith until it's completely replaced.
Strangler Fig in Action (Concept)
This conceptual code shows how an API Gateway might route requests, sending some to a new microservice and others to the legacy application.
public class LegacyApp {
public String handleRequest(String path) {
return "Legacy processing for " + path;
}
}
public class NewMicroservice {
public String handleRequest(String path) {
return "New service processing for " + path;
}
}
public class ApiGateway {
private LegacyApp legacyApp = new LegacyApp();
private NewMicroservice newService = new NewMicroservice();
public String routeRequest(String path) {
if (path.startsWith("/new-feature")) {
return newService.handleRequest(path);
} else {
return legacyApp.handleRequest(path);
}
}
}
public class Main {
public static void main(String[] args) {
ApiGateway gateway = new ApiGateway();
System.out.println(gateway.routeRequest("/old-feature/data"));
System.out.println(gateway.routeRequest("/new-feature/users"));
}
}Microservices: The Trade-offs
While powerful, microservices introduce new challenges:
- Operational Complexity: More services mean more deployments, monitoring, and logging.
- Distributed Data: Maintaining data consistency across multiple services can be tricky.
- Inter-Service Communication: Network latency and communication overhead.
- Testing: End-to-end testing becomes more complex.
It's not a silver bullet for all problems!
Check Your Understanding
Which of the following are valid strategies or principles for decomposing a monolithic application into microservices?
Lesson Summary
In this lesson, we explored the journey from monolithic applications to microservices.
- We understood the limitations of monoliths.
- Learned what microservices are and their benefits.
- Discovered key decomposition strategies: by business capabilities, using bounded contexts, and the Strangler Fig Pattern.
- Finally, we touched upon the challenges that come with adopting a microservices architecture.
Next up, we'll dive into how these independent services communicate!
Frequently asked questions
Is the “Decomposing Monoliths to Microservices” lesson free?
Yes — the full text of “Decomposing Monoliths to Microservices” is free to read here on the web, and the Spring Boot 4 Microservices & REST APIs course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Boot 4 Microservices & REST APIs course, upgrade to CoddyKit PRO.
What will I learn in “Decomposing Monoliths to Microservices”?
Learn strategies for breaking down large monolithic applications into smaller, independent services. You practise Spring Boot 4 Microservices & REST APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Spring Boot 4 Microservices & REST APIs?
No prior experience is required. Spring Boot 4 Microservices & REST APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Decomposing Monoliths to Microservices” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Spring Boot 4 Microservices & REST APIs lesson?
Yes. Every Spring Boot 4 Microservices & REST APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Decomposing Monoliths to Microservices
- Inter-Service Communication Basics
- Event-Driven Architectures Overview