Introduction to Microservices Architecture

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Introduction to Microservices Architecture

In this post, I will briefly explain Microservices Architecture by comparing it with Monolithic Architecture. In modern software development, choosing the right architecture is essential for achieving reliability, scalability, and maintainability. An application architecture is the high-level blueprint that defines how the components of an application are organized, how they communicate, and how they are deployed. A well-designed architecture enables teams to deliver features quickly, isolate system failures, and evolve the system as requirements change. In this chapter, we will explore:

• What is an Application, and what are the different types of Applications?
• The core differences between Monolithic and Microservices architectures.
• The real-world motivations for migrating from one architecture to another.
• How Microservices fit into modern application development.

What is an application?

An application is a collection of software programs, databases, and services designed to work together to help users accomplish tasks, such as:

• Shopping Online,
• Streaming Videos,
• Conducting Online Banking,
• Ordering Food, and more.

An application architecture defines the structure of the software, describing how different components interact to perform the desired functions. It also defines how to organize the codebase and manage business logic, data flow, and user interaction. At a high level, most applications consist of three primary layers:

• Presentation/User Interface (UI): This is the interface through which users interact with the application (e.g., web pages, mobile app, desktop GUI).
• Business Logic: The rules and operations that process and manipulate data.
• Data Layer: The part responsible for storing and retrieving persistent data (e.g., databases, file systems, caches).

While every system conceptually has these layers, how they are packaged and deployed varies significantly across different architectures. Today, two dominant architectural styles are:

• Monolithic Architecture
• Microservices Architecture

Types of Applications:

Applications can be categorized as web, mobile, or desktop applications:

• Web Applications: Delivered via browsers (e.g., e-commerce websites).
• Mobile Applications: Native or cross-platform apps on smartphones and tablets (e.g., ride-sharing apps).
• Desktop Applications: Installed on workstations or servers (e.g., accounting software).

Complex applications such as social media platforms (e.g., Facebook, Twitter), video streaming services (e.g., Netflix, YouTube), and enterprise resource planning (ERP) systems are examples that go beyond simple tasks like banking or shopping, often requiring distributed and scalable architectures.

What are Distributed Systems?

A distributed system is a system where components are located on different networked computers but work together to achieve a common goal by communicating through messages. So, any architecture where components run on different networked machines qualifies as distributed. Microservices architecture falls under distributed systems, where a monolithic application is broken into smaller, independent services communicating over a network.

Monolithic Architecture

In a monolithic architecture, the entire application is built as a single deployable unit, meaning all components (UI, business logic, and database interaction) are tightly integrated into one codebase. All components share the same database and run within the same process. While monolithic systems are initially simple to develop and deploy, they become more complex and challenging to manage as the application grows.

Understanding Monolithic Architecture with an E-commerce Example:

A single-tier system where all components are tightly coupled, and there is one unified database that interacts with all services is referred to as Monolithic Architecture. As shown in the below diagram, with monolithic architecture, all components are tightly coupled, sharing a single database.

UI Layer (Presentation Layer):

This is the topmost layer of the application where users interact with the system. It consists of web pages, mobile interfaces, or other types of graphical user interfaces (GUIs). In monolithic systems, the UI layer is tightly integrated with the business logic and data access layers, meaning that any change in business logic can affect the UI layer.

Business Logic Layer:

This layer contains the core functionality of the application. It is responsible for processing data and implementing business rules. In the diagram, this layer is divided into modules such as:

• Product Module
• Order Module
• Payment Module
• Inventory Module

Each module contains specific business logic for its respective functionalities. The business logic layer in a monolithic architecture is usually tightly coupled, meaning changes in one module might affect others. This is a challenge as the system grows.

Data Access Layer:

This layer is responsible for accessing and interacting with the database. It includes the logic required for querying, inserting, updating, and deleting data from the database. In monolithic systems, this layer communicates directly with a shared database (in this case, shown as the “Shared Database”).

In a monolithic application, the data access layer is often tightly integrated with the business logic and UI layers, meaning that any changes in one part of the system can have a ripple effect throughout the application.

Shared Database:

This is where the application’s data is stored. In a monolithic architecture, all components (UI, business logic, and data access layers) typically share a single database. All modules use this shared database to store and retrieve data.

In monolithic systems, scaling often involves replicating the entire application, including the database, which can become inefficient as the system grows.

Key Characteristics of Monolithic Architecture:

• Tightly Coupled: All layers are closely connected, meaning changes in one layer (e.g., business logic) can affect other layers (e.g., UI or data access).
• Single Deployable Unit: The entire application, including all layers (UI, business logic, data access), is packaged together and deployed as a single unit.
• Single Database: The application relies on a single, shared database, which can become a bottleneck as the system grows.

Advantages of Monolithic Architecture

• Easy to develop, test, and deploy in the early stages. Only one deployable unit to test and deploy.
• Internal method calls are faster than network calls.
• Popular frameworks (e.g., ASP.NET Core MVC) are optimized for monoliths.
• Ideal for small-scale applications with limited complexity.

Drawbacks of Monolithic Architecture:

• Scalability Limits: Scaling the application means scaling the entire system, not individual components.
• Tight Coupling: Components are tightly coupled, making modifying or updating individual modules harder without affecting the whole system.
• Reliability Risks: A bug in one module can bring down the entire application.
• Slower Releases: The entire system must be redeployed for small updates.

What is Microservices Architecture?

Microservices break down the application into smaller, loosely coupled services, each responsible for a specific business function. Each service is independently deployable, scalable, and maintainable, and typically communicates over a network using lightweight protocols such as HTTP.

Understanding Microservices Architecture with an E-commerce Example:

The microservices architecture shows a distributed system where services are decoupled and can be deployed independently. As shown in the diagram below, with microservices architecture, all components are decoupled, and each component has its own code base and database.

UI Layer:

The UI Layer is the top layer where users interact with the application. It can be a web interface, a mobile app, or another frontend interface. In this architecture, the UI layer communicates via APIs with multiple microservices (Product Service, Order Service, Payment Service, and Inventory Service).

Microservices (Product, Order, Payment, Inventory Services):

Each service in the diagram represents a distinct microservice that is responsible for a specific business function. The key idea here is that instead of having one large monolithic application, the application is broken down into smaller, independent services. Each of these services is self-contained and operates independently.

• Product Service: Handles product-related functionality like managing product details, categories, and listings.
• Order Service: Manages orders, order status, and transactions.
• Payment Service: Manages payment processing, including handling transactions and payment gateways.
• Inventory Service: Handles inventory management, including stock levels and product availability.

Each microservice consists of:

• Business Logic: The rules and operations related to the service’s specific functionality.
• Data Access Layer: This layer is responsible for interacting with its own database (this is isolated to each service). This ensures data independence between the services.

Communication Between Services (HTTP API & Message Broker):

The microservices communicate with each other and with the UI via HTTP APIs. This allows each service to be accessed independently, and the user interface can request specific functionality from the appropriate service.

• HTTP API: Each service exposes an API to the outside world (the UI or other services) using standard web protocols like HTTP. This is how the different microservices communicate with the UI or each other.
• Message Broker: This component is used for communication between microservices that need to be asynchronous or event-driven. It helps decouple services, ensuring that if one service fails, it doesn’t bring down the entire system. A message broker can manage events like when an order is placed, notify the inventory, or payment services.

Key Characteristics of Microservices Architecture:

• Independence: Each service has its business logic and data access layer. This allows services to be developed, deployed, and scaled independently.
• Decoupling: The services are loosely coupled, meaning changes in one service (e.g., adding new features to the Order Service) don’t require changes to other services (e.g., Inventory or Payment).
• Scalability: Each microservice can be scaled independently based on demand. For example, if the Order Service receives a high traffic volume, it can be scaled up independently without affecting other services.
• Fault Isolation: Since services are independent, a failure in one service does not affect others. For instance, a failure in the Payment Service doesn’t bring down the entire application.
• Communication Mechanism: Microservices communicate over APIs and event-driven mechanisms, making them more flexible and adaptable to different scenarios.

Challenges of Microservices Architecture:

• More complex to develop, test, and deploy due to the distributed nature of the services.
• Requires sophisticated mechanisms for inter-service communication. Requires robust service discovery, API gateways, and retry policies.
• More overhead in managing multiple services, especially for data consistency.
• Additional infrastructure is needed for service discovery, centralized logging, and API gateways, which adds complexity and overhead to the development process.

Real-World Examples of Microservices Architecture

Netflix: Initially a monolithic application, Netflix migrated to a microservices architecture to handle scalability and independent deployment needs. The move enabled Netflix to scale its services globally and reduce deployment downtime. Netflix migrated to hundreds of microservices on AWS to handle global scale, personalized streaming, and rapid feature launches.

Amazon: Amazon started with a monolithic architecture but eventually transitioned to microservices to support its growing product catalogue and user base. By adopting microservices, Amazon scales specific services like payment processing without affecting other parts of the platform.

Uber: Uber adopted microservices to handle the complexity of its application, which includes driver matching, ride tracking, payments, and ratings. The shift enabled Uber to scale individual components without disrupting the entire platform.

It is important to understand why these companies transitioned from monolithic systems. For example, Netflix required scalable deployment mechanisms as their global user base grew, which monolithic architectures struggled to handle.

Monolithic vs Microservices Architecture: A Detailed Comparison:

When and Why Should We Move from Monolith to Microservices Architecture?

Migrating from a monolithic architecture to microservices becomes necessary when the application faces challenges like scaling issues, performance bottlenecks, or slow development cycles due to tightly coupled components. Migration allows teams to work independently on different services and scale them individually.

When to Migrate:

Migration becomes essential when:

• Scale: When the system becomes too large for a single unit to scale efficiently.
• Performance: If certain application parts require more resources than others, microservices allow those parts to scale independently.
• Independent Deployment: Microservices allow teams to deploy their services independently without waiting for other teams.
• Flexibility: Microservices support using different technologies for different services, offering more flexibility in development.

Why Migrate:

• Faster Releases: Microservices support continuous delivery and deployment, making it easier to release new features without disrupting the whole system.
• Fault Isolation: In microservices, failures in one service do not affect others, improving overall system reliability.
• Better Resource Utilization: Microservices optimize specific services for performance, leading to better resource utilization.

Choosing Between Monolithic and Microservices Architecture:

The decision between monolithic and microservices architecture depends on the application’s size, the business’s complexity, and the development team’s structure. Monolithic architecture works well for small, simple applications and small teams, while Microservices are best suited for large, complex applications requiring scalability and flexibility.

So, Microservices Architecture offers flexibility, scalability, and fault tolerance by breaking down the application into smaller, independent services. This architecture is particularly useful for large, complex systems that require frequent updates and scaling. However, managing multiple services introduces new complexities that must be addressed with proper infrastructure and practices.

In the next article, I will discuss ASP.NET Core Web API Fundamentals with Examples. In this article, I will briefly explain Microservices Architecture by comparing it with Monolithic Architecture. I hope you enjoy this article, Introduction to Microservices Architecture.