Architectural Evolution: From Monolithic Constraints to Microservices Flexibility

A monolithic application is designed as a single entity, where all parts of the application are interconnected and dependent on each other. It means that all the elements of the application such as user interfaces, business logic, data access layers, and external APIs are part of a single codebase that is deployed together. Monolithic application components are tightly coupled, shared resources, Single Deployment unit, etc.

Components of a Monolithic Application

Typically, a monolithic application will contain various components:

• Presentation Layer: Handles the user interface (UI), which may include HTML, CSS, and JavaScript.
• Business Logic Layer: Contains the core functionality of the application, handling the actual business rules and processes.
• Data Access Layer: Interacts with the database, handles CRUD (Create, Read, Update, Delete) operations, and manages database connections.
• Shared Database: A single database that all components interact with.

Advantages of Monolithic Applications

• Simpler Development: For small applications, it’s easier to develop and test a single codebase since all components are together.
• Simpler Deployment: Everything is packaged together, there’s only one deployment, reducing complexity for small teams or applications.
• Performance: Monolithic applications perform better in simple use cases where all components are within the same application and interact directly without the overhead of network calls.

Disadvantages of Monolithic Applications

• Limited Scalability: Monolithic applications are difficult to scale, as they require scaling the entire application even if only one part needs additional resources.
• Slow Development as Complexity Grows: As the application grows, the codebase becomes larger and more difficult to manage, making it harder to add new features, fix bugs without affecting other parts of the application.
• Tight Coupling: Components are tightly coupled, when changes to one part of the application can have ripple effects on other parts.
• Longer Deployment Cycles: Even minor changes require redeploying the entire application, which increases downtime and the risk of introducing errors.
• Technology Stack Lock-In: All parts of the application use the same stack; it’s challenging to adopt new technologies or frameworks for specific components.
• Monolithic applications are suitable for small to medium-sized systems, but as complexity grows, organizations may move toward microservices for better scalability and flexibility.

Complications in Monolithic Application

Scalability

Monolithic applications are challenging to scale effectively because the entire application is deployed as a single unit. Even if only one part of the application needs more, you must scale the entire application. In a monolithic architecture, scaling usually involves adding more resources (CPU, memory) to the server. However, vertical scaling has limitations, and there’s a threshold beyond which it becomes expensive and inefficient.

Complexity as the Application Grows

All components are tightly coupled, meaning that changes in one module can affect others. This tight coupling makes it difficult to isolate issues and work on specific parts of the system without impacting the entire application.

Difficulty in Continuous Deployment

Single Deployment Unit: The entire application is packaged and deployed together. This means that even a small change in one module requires the entire application to be redeployed. This increases the risk of introducing bugs or downtime.

Longer Deployment Times: Deploying a monolithic application can be time-consuming because the entire application must go through the build, test, and deployment pipeline. This slows down continuous deployment and creates bottlenecks in delivering new features or fixes.

Downtime During Deployment: Since the whole application must be deployed at once, downtime during deployment is a common issue. This can be mitigated through techniques like blue-green deployment, but it adds complexity to the deployment process.

Limited Flexibility in Technology Stack

In a monolithic application, the entire system typically relies on a single technology stack for development, which can limit flexibility. Developers are usually locked into a single programming language and framework for all modules, even if different parts of the application would benefit from different technologies. For example, you might want to use Python for machine learning features and Java for the core application, but in a monolith, this flexibility is restricted.

As the application grows, upgrading frameworks and libraries becomes difficult because the entire system relies on them. Often, technical debt accumulates as parts of the application are tied to outdated technologies.

Poor Fault Isolation

Monolithic architecture, a failure in one part of the system can bring down the entire application.

Single Point of Failure: If a critical service or module fails the whole system may become unavailable, even if other services are still functioning correctly because of the tight coupling and shared resources, it’s harder to isolate and handle failures in a monolithic system. A failure in one module can cascade and affect other parts of the application.

Performance Bottlenecks

Monolithic applications can do impact from performance issues due to the tight coupling and lack of modularity:

All parts of the application share the same CPU, memory, and database resources. A bottleneck in one part of the application can degrade the performance of the entire system. For example, a poorly optimized query in one module can slow down the whole system.

Database Contention: In a monolithic application, multiple modules often share a single database. As more users interact with the system, database contention can lead to performance degradation.

Database Scalability and Management

The database is a single point of failure in a monolithic application. If it crashes or experiences issues, the entire application can go down. Scaling the database in a monolithic architecture is another very harder part because you can’t easily distribute the load across multiple databases without significant changes to the application. Making schema changes in the database can be tricky because the changes might affect multiple parts of the application that rely on shared tables.

Dependency Management

Different modules might require different versions of the same third-party library. In a monolithic architecture, managing these dependencies becomes challenging without causing version conflicts or breaking other parts of the system. Upgrading dependencies across the entire system can introduce significant risks. Testing must be thorough to ensure that nothing breaks after an upgrade, making the process slow and risky.

Use Case Scenario of a Monolithic E-commerce Application

Let’s look at a Monolithic E-commerce Application to understand its architecture and how the various components function.

User Authentication Service: Handles user login, registration, password management, and authentication.

• Tasks: Verifying user credentials, creating sessions, and handling user-specific data.
• Database Interaction: Stores user data, encrypted passwords, and session details.

Product Catalog Service: Manages product listings, categories, pricing, inventory, and product details.

• Tasks: Fetching product details from the database, updating inventory, managing discounts, etc.
• Database Interaction: Reads and writes product data, such as product names, descriptions, and stock quantities.

Shopping Cart Service: Allows users to add and remove items from their shopping cart.

• Tasks: Managing the state of the shopping cart, calculating totals, handling product availability.
• Database Interaction: Stores temporary shopping cart data associated with each user.

Payment Processing Service: Manages payments through integrations with payment gateways like Stripe or PayPal.

• Tasks: Handling payment confirmation, credit card transactions, error handling, and integration with payment providers.
• Database Interaction: Stores transaction and order history data.

Order Management Service: Responsible for order placement, tracking, and fulfillment.

• Tasks: Creating and updating order statuses, managing shipping and delivery information, and interacting with logistics providers.

Database Interaction: Stores order details, shipping addresses, and tracking information.

Review and Ratings Service: Allows users to submit reviews and ratings for products they have purchased.

• Tasks: Handling user feedback, displaying product ratings, and moderating reviews.
• Database Interaction: Stores reviews and ratings data.

Monolithic Workflow

1. User Interacts with UI: A user interacts with the e-commerce website, logging in and adding items to their shopping cart.
2. Backend Communication: The user authentication service checks credentials and updates the session. The shopping cart service interacts with the product catalog to check product availability.
3. Payment Processing: The user proceeds to payment, where the payment processing service interacts with a third-party gateway (e.g., PayPal), and once the payment is successful, the order management service updates the order status.
4. Database: Every service is writing to or reading from the same shared database, ensuring all data (products, users, orders, etc.) is stored and available for the other services to use.

Conclusion

As larger Monolithic applications have more challenges and difficulties, it can be particulary advantageous to transition from a Monolithic to a Microservice architecture. In a microservices-based system each service is decoupled and functions independently, Services can be developed, deployed, and scaled independently, improving flexibility and reducing the risk of system-wide failures. Microservices allow you to use different technology stacks for different services, enabling teams to choose the best tool for the job.

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