feat(task-8): Integration with RDS

[SanjanaR-16]

Task 8 — NestJS Cart Service on AWS Lambda + RDS (PostgreSQL)

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Task 8.1 — Lambda + API Gateway

• Added src/lambda.ts — serverless entrypoint that bootstraps NestJS via @codegenie/serverless-express and exposes a handler for Lambda
• Created infra/ — standalone CDK project (separate from the NestJS app) containing:
  • NodejsFunction (Node 20.x) pointing at src/lambda.ts
  • RestApi with a catch-all proxy LambdaIntegration routing all HTTP methods to the Lambda
• Live API URL: https://jncym2xiu8.execute-api.us-east-1.amazonaws.com/prod/

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Task 8.2 — RDS PostgreSQL + VPC + Security Groups

• VPC with public + private subnets across 2 AZs with a NAT gateway for Lambda egress
• DatabaseInstance using PostgresEngineVersion.VER_16_3, t3.micro, placed in private subnets
• Dedicated security groups: Lambda SG → DB SG restricted to port 5432 only (least-privilege)
• DB credentials auto-generated and stored in AWS Secrets Manager

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Task 8.3 — TypeORM Cart + CartItem Models + DB Integration

Entities:

Table	Columns
carts	id UUID PK, user_id varchar not null, status enum (OPEN/ORDERED)
cart_items	id UUID PK, cart_id FK → carts.id, product_id varchar not null, count int

Service changes:

• CartService fully rewritten from in-memory storage to async TypeORM repository pattern
• ProductCatalogService added — fetches product details from the product service by ID to preserve the { product, count } response shape expected by the frontend
• Cart checkout transitions status to ORDERED instead of deleting the row

Environment variables:

• DB connection details (DB_HOST, DB_PORT, DB_USER, DB_PASSWORD, DB_NAME, DB_SSL, DB_SYNC) injected into Lambda via CDK environment property
• PRODUCT_SERVICE_URL configurable via CDK context flag -c productServiceUrl=...
• Frontend apiPaths.ts updated to use the deployed cart API URL (overridable via VITE_CART_SERVICE_URL)

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Link:SanjanaR-16/AWS_frontend#3