What is the difference between microservices architecture and monolithic architecture?

Monolithic architecture:

• A single, self-contained application.
• All components are tightly coupled.
• Deployment occurs as a single unit.
• Scaling is usually horizontal (increasing the number of application instances).
• Development, testing, and debugging are simpler for small projects.
• Difficulties with scaling individual parts, updating, and refactoring a large monolith.

Microservices architecture:

• A set of small, independent services.
• Each service performs a specific business function.
• Services communicate with each other (e.g., via HTTP, message queues).
• Services are deployed independently.
• Each service can be scaled separately.
• The technology stack may differ for different services.
• Management complexity of a distributed system, ensuring data consistency, monitoring, testing.

Key differences:

Attribute	Monolithic architecture	Microservices architecture
Size	Large	Small
Independence	Low	High
Deployment	Single	Independent
Scaling	Horizontal (all)	Per service
Fault tolerance	Low (failure of part means failure of all)	High (service failure does not lead to system failure)
Technologies	Single stack	Different stacks
Management complexity	Low (for small systems)	High (for distributed systems)

# Example structure of a monolithic application
# The application contains all modules in one place
class UserManagement:
    def create_user(self):
        pass

class OrderProcessing:
    def process_order(self):
        pass

class PaymentGateway:
    def process_payment(self):
        pass

class MonolithicApp:
    def __init__(self):
        self.user_management = UserManagement()
        self.order_processing = OrderProcessing()
        self.payment_gateway = PaymentGateway()

    def run(self):
        # All functionality works within a single process
        pass

# Example structure of a microservices architecture
# Separate services for user, orders, and payments
# These services are deployed and operate independently
class UserServiceClient:
    def create_user(self):
        # Call to remote user service
        pass

class OrderService:
    def process_order(self):
        # Order processing logic
        pass

class PaymentServiceClient:
    def process_payment(self):
        # Call to remote payment service
        pass

# Separate processes or containers for each service
# UserService.run()
# OrderService.run()
# PaymentService.run()