Spring Boot: Practical experience in migrating from monolith to microservices system
Tags: webdev, microservices, monolithic, spring
Published: 2023-09-21 08:52:20

As technology evolves and business requirements change, many organizations find themselves facing the challenge of migrating from monolithic architectures to microservices. This transition can be daunting, but it is a necessary step to increase scalability, agility, and maintainability. In this article, I'll share my experience in the past to microservice in real project I worked, focusing on the solution architecture aspect, to guide you through the process of migrating from a monolith architecture to a microservices system.

## Why Migrate to Microservices?

Before diving into the migration process, it's crucial to understand the benefits of adopting a microservices architecture:

1. **Scalability**: Microservices enable horizontal scalability, allowing you to independently scale components based on their workload.
2. **Agility**: Smaller, loosely coupled services make it easier to release updates and introduce new features, reducing time-to-market.
3. **Fault Isolation**: Microservices isolate failures, ensuring that issues in one service don't bring down the entire system.
4. **Technology Flexibility**: Different microservices can use various technologies, enabling you to choose the best tool for each specific task.
5. **Improved Maintainability**: Smaller codebases are easier to manage, test, and maintain over time.
6. **Enhanced Resilience**: Microservices can be designed for redundancy and failover, increasing the overall system's reliability.
7. **Cost Efficiency**: You can optimize resource allocation, leading to cost savings in terms of infrastructure usage.

## The Migration Roadmap With Simple Mind

*Before breakdown the main application into microservices, the concept of Service is mentioned which means the service class in the business layer. You will be quite familiar when working with Spring.*


![Monolithic Architecture](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/e2h5511ecfu1hoh6no7e.png)

- Step 1: **Identify Microservices**: Identify potential microservices within the monolith, considering business capabilities and domain-driven design principles.

- Step 2: In the service and repository layers, group them based on predefined domains.

```
Example:
Domain 1 (order-service) includes Service 1, Repository 1, and Repository 2.
Domain 2 (account-service) includes Service 2 and Repository 3.
```
- Step 3: Split domain-related tables into a new database. If you want a system deployed with zero downtime, you can apply the pub-sub model or use database replication when splitting the database.
- Step 4: Next, create a new Spring Boot application and copy all the related classes (services and repositories). Also, remember to create controller classes to associate with the service layer and expose APIs for other applications to use.

```
Example: When creating the order-service (spring boot application), copy Service 1, Repository 1, and Repository 2 to this new project.

```
- Step 5: When the new application is started, in Main Application, instead of communicating with business layer, you can use RestTemplate to call API on new application


![Microservices Architecture](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/9femx9bowkg43s5pkthd.png)

And so on, you continue to gradually separate different domains into independent service applications, communicating with each other via HTTP or Message Broker.

The above is the first step for us to start thinking about transitioning from the monolithic model to microservices. This is what I did when I joined a product-building team at a startup. Monolithic architecture is suitable for creating MVP instances for testing a new business model.
I believe that when the model has taken shape, clearly, the MVP application has been running stably, and the size of the technical team has increased, it's time for us to consider expansion and transformation.

_I'm also a normal software engineer and there will still be mistakes but this is probably a good experience for me, hoping to receive contributions from the community so I can have a better perspective._

Wish you have a good working day!
Jacky