What is the difference between microservices and normal services?

The distinction between microservices and "normal" services (often referred to as monolithic architectures or traditional SOA - Service-Oriented Architecture) primarily lies in their design philosophy, scalability, and how functionality is organized and deployed within an application. Here’s a detailed comparison:

Microservices

1. Modular Structure: Microservices architecture breaks down an application into small, autonomous services, each implementing specific business functionality. These services are independently deployable, scalable, and maintainable.

2. Technology Diversity: Each microservice can be developed using the most appropriate programming language, database, and tools for its specific requirements, allowing for a polyglot architecture.

3. Decentralized Data Management: Microservices often manage their own database and state, leading to decentralized data management. This approach avoids database schema conflicts and data model coupling between services.

4. Independent Deployment: Microservices can be deployed independently of one another. This allows for frequent and rapid deployment of individual services without affecting the entire application.

5. Fault Isolation: Failures in one service do not necessarily bring down the entire system, improving the application's overall resilience.

6. Scalability: Microservices can be scaled independently, allowing for more efficient use of resources and improved response times for specific functionalities experiencing high demand.

Normal Services (Monolithic or Traditional SOA)

1. Unified Structure: In a monolithic architecture, all the application's functionalities are tightly integrated into a single service. In traditional SOA, services are more modular than monoliths but still tend to be larger and less fine-grained than microservices.

2. Consistent Technology Stack: Applications are typically built using a single programming language and technology stack, which can limit the ability to adopt new technologies or frameworks.

3. Centralized Data Management: Monolithic applications and traditional SOA often rely on a single database for all data storage needs, leading to tight coupling between different parts of the application.

4. Coupled Deployment: Deploying a small change generally requires redeploying the entire application, which can slow down development and increase the risk of deployment-related issues.

5. Shared Failure Risk: In monolithic architectures, a bug or failure in any module can potentially affect the entire application, leading to downtime and reduced reliability.

6. Scalability Challenges: Scaling a monolithic application usually means scaling the entire application, even if only part of it is experiencing increased demand. This can lead to inefficient resource use.

Conclusion

Microservices offer a more granular and flexible approach to building applications, with benefits in terms of scalability, resilience, and technology diversity. However, they also introduce complexity in terms of service communication, data consistency, and infrastructure overhead. Monolithic architectures or traditional SOA, while simpler to develop and deploy, can become unwieldy as applications grow, making it harder to implement new features, technologies, and scale efficiently. The choice between microservices and traditional services depends on various factors, including the application's size, team expertise, and specific business requirements.