• Refer to Lab1.pdf and Lab2.pdf for detailed project requirements.
• Refer to Report.pdf for an overview of the project and its components.
• Specific documentation for each service is available in their respective repositories.

This project series focuses on building and enhancing Bazar, a multi-tier online bookstore system. Initially, Bazar starts as a small, minimalistic online bookstore with a catalog of only four books. The project progressively adds complexity and functionality, such as replication, caching, and containerization, to handle higher demand and improve performance. The goal is to deepen your understanding of distributed systems, web microservices, and performance optimization techniques.

• bazar-gateway-service: Handles user interactions and routes requests to backend services.
• bazar-catalog-service: Manages the book catalog, including stock levels and book details.
• bazar-order-service: Manages order requests, verifies stock availability, and processes purchases.
• .github: Stores project documentation, including design documents.

Each service includes its own docker-compose.yml file for development. The gateway service acts as the main entry point, coordinating all services.

The Bazar system uses a microservices-based architecture, with each service responsible for a specific domain of the application. These services communicate with each other using REST. The system includes caching and replication to improve performance and ensure fault tolerance.

Excalidraw Link

1. Gateway Service:

   • Acts as the entry point for all client traffic.
   • Handles routing, caching, and load balancing for the backend services. It uses Round-Robin load balancing algorithm to distribute load evenly among nodes.
   • Ensures high availability and improved performance through in-memory caching and intelligent request distribution.
   • An in-memory cache in the Gateway Service stores frequently accessed data (e.g., book details). It uses LRU (least recently used) method to eliminate data when cache size limit is hit.

2. Catalog Service:

   • Maintains the book catalog, including details such as stock, price, and topic.
   • Implements a primary-backup replication for fault tolerance and performance:
     • The primary instance handles all write operations, and syncs updates with the backup.
   • Integrates with the gateway for cache invalidation upon updates.

3. Order Service:

   • Processes purchase requests, verifies stock availability, and updates catalog data.
   • Uses multiple replicas to handle increased loads.
   • Works with the gateway for balanced request distribution.

• Search and Query:

  • The gateway queries the primary Catalog Service for book details.
  • Frequently accessed queries are cached to reduce load on the backend.

• Purchases:

  • Purchase requests are routed through the gateway to the Order Service.
  • The Order Service communicates with the Catalog Service to validate and update stock levels.

• Cache Invalidation:

  • When the Catalog Service processes an update, it notifies the Gateway Service to invalidate relevant cache entries.

• Create a Simple Online Book Store: Design and implement Bazar.com with a small catalog of four books.
• Multi-Tier Architecture: Set up a two-tier architecture with a front-end gateway and back-end services (catalog and order).
• Microservices Design: Implement each component as an independent microservice.
• REST API: Expose all operations as HTTP REST interfaces.

1. Gateway Service: The front-end service that:

   • Accepts user requests and routes them to the appropriate backend service.
   • Supports operations:
     • search(topic): Finds books by topic.
     • info(item_number): Provides details about a specific book.
     • purchase(item_number): Initiates the purchase of a specific book.

2. Catalog Service: Maintains the catalog with details for each book (stock, cost, topic).

   • Supports operations:
     • query: Look up books by topic or item number.
     • update: Update stock or pricing information.

3. Order Service: Manages purchase requests and stock verification.

   • purchase(item_number): Checks stock availability and decrements stock upon purchase.

• Enhance System Performance: Introduce replication, caching, and containerization to improve Bazar.com’s scalability and reduce latency.
• Replication and Load Balancing: Add replicas for catalog and order services, and implement load balancing in the gateway.
• Caching: Add an in-memory cache at the gateway to serve recent read requests efficiently.
• Containerization (Optional): Package each component as a Docker container for ease of deployment.

1. Gateway Service (Enhanced):

   • Introduce in-memory caching for recent queries to reduce load on backend services.
   • Implement load balancing to distribute requests among replicated catalog and order servers (e.g., using round-robin or least-loaded strategies).

2. Catalog and Order Services (Replicated):

   • Replicate both services across multiple instances to improve request handling capacity.
   • Ensure consistency across replicas through internal synchronization protocols.

3. Cache Consistency:

   • When a backend database entry is updated, backend servers invalidate relevant cached entries.
   • Implement a cache replacement policy (e.g., LRU) if a cache size limit is set.

4. Optional Dockerization:

   • Containerize each component (gateway, catalog, order, and cache if separate).
   • Upload Docker images to the GitHub repository, allowing easy deployment on any compatible environment.

• GET /search/<topic>: Search for books by topic.
• GET /info/<item_number>: Get information about a specific book.
• POST /purchase/<item_number>: Purchase a specific book.

• GET /query?topic=<topic>: Query books by topic.
• GET /query?item_number=<item_number>: Query book details by item number.
• PUT /update/<item_number>: Update stock or price information.

• POST /purchase/<item_number>: Handle purchase requests, verify stock, and update quantities.

1. Clone Repositories:
   • Clone the necessary repositories for each service (gateway, catalog, order).
2. Configuration:
   • Set up environment variables and configurations as specified in each service’s README.md.
3. Start Services:
   • Use the provided docker-compose.yml in the bazar-gateway-service repository to start all services together.
4. Accessing the Application:
   • Gateway Service: Access the gateway at http://localhost:5000.
5. Testing and Verification:
   • Use the tests.http file or a tool like Postman to test the API endpoints.

Each service can also be run individually using its own docker-compose.yml file for isolated development and testing.

This project is developed as part of an academic exercise in Distributed Operating Systems. All rights reserved by the authors.