Bazar Gateway Service

The Bazar Gateway Service is a Node.js microservice that acts as the entry point for clients to interact with the Bazar online bookstore. It connects with the bazar-catalog-service to retrieve book details and with the bazar-order-service to process book purchases.

Features

• Book Search: Allows clients to search books by topic via the Catalog Service.
• Book Details: Provides detailed information about specific books.
• Purchase Processing: Facilitates purchase requests via the Order Service.
• Load Balancing: Distributes requests across multiple Order & Catalog Service instances.
• Cache Optimization: Implements a small in-memory cache for frequently accessed data to reduce response times.

Architecture

The Gateway Service is designed to interact with a distributed system comprising multiple services. The key components and their roles in the architecture are:

1. Gateway Service:

   • Acts as the central access point for all client requests.
   • Balances the load between multiple Service instances.
   • Maintains a small in-memory cache to reduce redundant requests to downstream services.

2. Catalog Service:

   • Exposes two instances:
     • Primary Instance: Handles queries and all of updates.
     • Backup Instance: Synchronizes with the primary and serves as a query replica.
   • Updates triggered by the Gateway Service ensure cache invalidation via the CACHE_INVALIDATE_URL.

3. Order Service:

   • Processes purchase requests.
   • Multiple instances allow for load balancing and fault tolerance.

Environment Variables

The following environment variables configure the Gateway Service:

• General Settings:

  • PORT (default: 5000): The port on which the gateway service runs.

• Catalog Service Configuration:

  • CATALOG_SERVICES: A comma-separated list of URLs for catalog services (e.g., http://bazar-catalog-primary:5001,http://bazar-catalog-backup:5001).
  • CACHE_SIZE (default: 3): The maximum number of items to store in the in-memory cache for catalog data.

• Order Service Configuration:

  • ORDER_SERVICES: A comma-separated list of URLs for order services (e.g., http://bazar-order-service-1:5002,http://bazar-order-service-2:5002).

Endpoints

Search for Books by Topic

• GET /search/:topic

  Searches for books in the catalog by topic.

  • Response:
    • Success: Returns a JSON array of books that match the topic.
    • Failure: { "error": "Failed to search books" }

Get Book Details

• GET /info/:item_number

  Retrieves details for a specific book by item_number.

  • Response:
    • Success: Returns a JSON object with the book’s details.
    • Failure: { "error": "Failed to fetch book info" }

Purchase a Book

• POST /purchase/:item_number

  Initiates a purchase request for a book by item_number.

  • Request Body: { "qty": 1 }

  • Response:

    • Success: { "message": "Purchased <quantity> book(s): <book title>" }
    • Failure: { "error": "Failed to process purchase" }

Running with Docker Compose

The gateway service is part of a multi-service Docker Compose setup that includes the catalog-service and order-service.

Step 1: Start the Services

To build and run the gateway, catalog, and order services together, navigate to the project directory containing the docker-compose.yml file and run:

docker-compose up --build

This command will:

• Build fresh images for bazar-gateway-service, bazar-catalog-service, and bazar-order-service.
• Start each service in its own container and connect them over a shared network.
• Expose the gateway service on port 5000, the catalog service on port 5001, and the order service on port 5002.

Step 2: Access the Gateway Service

Once the services are running, you can access the gateway at http://localhost:5000.

Example Requests

1. Search for Books by Topic:

   GET http://localhost:5000/search/distributed%20systems
   

2. Get Book Details:

   GET http://localhost:5000/info/1
   

3. Purchase a Book:

   POST http://localhost:5000/purchase/1
   Content-Type: application/json
   
   {
   "qty": 2
   }