REST_API_microservices.md

Microservices

C++ microservices are less common compared to microservices built using languages like Java, Python, or Node.js, which are more popular for web applications and cloud-native services. However, C++ is still used for microservices, especially in scenarios that require high performance, low latency, or extensive computational power, such as:

1. Finance: High-frequency trading systems or any system that demands low-latency communication can benefit from C++'s performance.
2. Telecommunications: Systems like network equipment or infrastructure services may use C++ for efficiency.
3. Embedded and IoT: C++ is used in devices where hardware-level interaction and performance optimization are critical.

Monolithic Software Example in C++

In a monolithic architecture, all components of the application are tightly coupled and run as a single unit. Let's assume we are building a simple e-commerce application. In a monolithic design, all components—user authentication, order management, product catalog, and payment processing—are integrated into one executable.

Monolithic Architecture (C++)

#include <iostream>
#include <string>
#include <vector>

class User {
public:
    std::string name;
    std::string email;

    User(std::string name, std::string email) : name(name), email(email) {}

    void displayUserInfo() {
        std::cout << "User: " << name << ", Email: " << email << std::endl;
    }
};

class Product {
public:
    std::string name;
    double price;

    Product(std::string name, double price) : name(name), price(price) {}

    void displayProduct() {
        std::cout << "Product: " << name << ", Price: $" << price << std::endl;
    }
};

class Order {
public:
    User user;
    std::vector<Product> products;

    Order(User user, std::vector<Product> products) : user(user), products(products) {}

    void displayOrder() {
        std::cout << "Order placed by " << user.name << " for:" << std::endl;
        for (auto &product : products) {
            product.displayProduct();
        }
    }
};

class Payment {
public:
    void processPayment(double amount) {
        std::cout << "Processing payment of $" << amount << std::endl;
    }
};

class ECommerceApp {
public:
    void run() {
        // User registration
        User user("John Doe", "[email protected]");

        // Product catalog
        Product product1("Laptop", 1200.50);
        Product product2("Headphones", 200.99);

        // Create order
        std::vector<Product> products = {product1, product2};
        Order order(user, products);
        order.displayOrder();

        // Payment processing
        Payment payment;
        payment.processPayment(product1.price + product2.price);
    }
};

int main() {
    ECommerceApp app;
    app.run();
    return 0;
}

Key Aspects:

• All functionalities (user management, product catalog, order management, and payment) are part of a single executable.
• Any change requires recompiling and redeploying the whole application.
• Hard to scale individual components independently.

---

Microservice Alternative in C++

In a microservices architecture, each functionality is broken down into small, independently deployable services. Let's split the monolithic application into different services.

1. User Service (Handles user authentication and management)
2. Product Service (Handles product catalog)
3. Order Service (Handles orders)
4. Payment Service (Processes payments)

Each service can be written in C++ but will run as a separate process, possibly communicating via HTTP (e.g., using REST APIs).

Example: Microservices Setup

1. User Service (user_service.cpp)

#include <iostream>
#include <string>

class UserService {
public:
    std::string getUserInfo() {
        return "John Doe, [email protected]";
    }
};

int main() {
    UserService userService;
    std::cout << "User info: " << userService.getUserInfo() << std::endl;
    return 0;
}

2. Product Service (product_service.cpp)

#include <iostream>
#include <string>

class ProductService {
public:
    std::string getProductCatalog() {
        return "Product: Laptop, Price: $1200.50\nProduct: Headphones, Price: $200.99";
    }
};

int main() {
    ProductService productService;
    std::cout << "Product Catalog:\n" << productService.getProductCatalog() << std::endl;
    return 0;
}

3. Order Service (order_service.cpp)

#include <iostream>
#include <string>

class OrderService {
public:
    void createOrder() {
        std::cout << "Order created for: John Doe\nProducts: Laptop, Headphones" << std::endl;
    }
};

int main() {
    OrderService orderService;
    orderService.createOrder();
    return 0;
}

4. Payment Service (payment_service.cpp)

#include <iostream>

class PaymentService {
public:
    void processPayment(double amount) {
        std::cout << "Processing payment of $" << amount << std::endl;
    }
};

int main() {
    PaymentService paymentService;
    paymentService.processPayment(1401.49);
    return 0;
}

Microservices Communication

In the microservice architecture, services would typically communicate using HTTP or gRPC. For example, OrderService might call UserService to retrieve user info, or PaymentService might be called to process payments after an order is placed.

The implementation of communication could be handled using REST API frameworks like:

• Crow (for RESTful communication)
• gRPC (for high-performance communication)