DynamoDB Combined with Lambda & API Gateway | Overview.

 DynamoDB Combined with Lambda & API Gateway - Overview

Scope:

• Intro,
• Core Concepts,
• When combined with  Lambda plus API Gateway,
• Request Flow (Deep Dive),
• Common Architectural Patterns,
• Security Considerations,
• Performance & Scaling,
• Observability & Operations,
• Sample High-Level Architecture.

Intro:

• Combining DynamoDB with Lambda and API Gateway is a popular architecture for building fully serverless web application backends and microservices. 
• This pattern allows twtech to create scalable, cost-effective, and low-maintenance APIs that can handle a wide range of use cases.
• This is the most common entry point for building serverless APIs.

 Core Concepts

• Amazon API Gateway: Fully managed service for creating REST, HTTP, and WebSocket
• APIs. It Handles request routing, throttling, caching, authentication, and monitoring.
• AWS Lambda: its Event-driven, serverless compute service, executes code in response to events (like an HTTP request via API Gateway).
• No servers to manage, scales automatically, and twtech only pay for execution time.

When combined with  Lambda plus API Gateway

•  API Gateway will act as the "front door" (routing, auth, transformation).
• Lambda will execute business logic.
• Together (AWS Lambda with API Gateway), they form a serverless microservice/API pattern.

 Request Flow (Deep Dive)

1. Client Request:
   User hits https://api.twtechapp.com/resource.
2. API Gateway Processing:
• Matches resource & method (/resource → GET).
• Handles authentication/authorization (IAM, Cognito, JWT, API keys, custom authorizers).
• Applies request validation & throttling.
• Optionally transforms request payload using Mapping Templates (VTL).
3. Lambda Execution:
• Lambda receives event payload in JSON (includes method, headers, body, path params).
• Executes code (Python, Node.js, Go, Java, etc.).
• Connects to backend services (DynamoDB, RDS, S3, Step Functions, etc.).
• Returns response object.
4. API Gateway Response Handling:
• Can map Lambda’s response to client-facing response.
• Handles errors (4xx, 5xx).
• Optionally cache responses in API Gateway Cache.
5. Client Receives Response.

 Common Architectural Patterns

• CRUD over DynamoDB
  API Gateway → Lambda → DynamoDB
  (for simple REST APIs with low ops overhead).

• Request/Response Transformation
  Use mapping templates to transform XML ↔ JSON or strip headers.
• Authentication via JWT/Cognito
  API Gateway → Lambda Authorizer (JWT validation) → Lambda backend.
• WebSocket APIs
  Real-time communication: API Gateway WebSocket → Lambda → backend.
• Lambda Proxy Integration
  Simplest: API Gateway forwards entire HTTP request to Lambda.
  (twtech handles parsing headers/body yourself).

Security Considerations

• Authentication: Use Cognito User Pools, OIDC providers, or Lambda authorizers for JWT validation.
• Authorization: Use IAM policies, resource policies, or fine-grained access control.
• Rate Limiting & Throttling: API Gateway enforces per-client quotas.
• WAF (Web Application Firewall): Protects against SQLi/XSS, bot traffic.
• VPC Access: Lambda can run in private subnets to connect to RDS/ElastiCache.

 Performance & Scaling

• Cold Starts:
• Lambda "cold start" latency (10–300ms depending on runtime & VPC).
• Mitigations: Provisioned Concurrency, lighter runtimes (Node.js, Go).
• Throughput:
• API Gateway scales to tens of thousands of requests/sec.
• Lambda concurrency is regional (default 1,000, can request quota increases).
• Caching:
• API Gateway cache can reduce Lambda invocations.
• DynamoDB Accelerator (DAX) can help with hot reads.
• Payload Limits:
• API Gateway max payload: 10 MB (REST/HTTP), 128 KB (WebSocket).
• For larger payloads, use S3 pre-signed URLs.

 Observability & Operations

• Logging: CloudWatch Logs for both API Gateway and Lambda.
• Tracing: AWS X-Ray for distributed tracing.
• Metrics: API Gateway provides latency, 4xx/5xx counts; Lambda provides duration, invocations, errors.
• CI/CD: Commonly automated via SAM (Serverless Application Model), CDK, Terraform, or Serverless Framework.
• Testing: Use Postman/Insomnia for API testing, or AWS Console Test tool.

Sample High-Level Architecture

Client → API Gateway → Lambda → DynamoDB

                           ↘ S3

                           ↘ SNS/SQS

                           ↘ RDS (via VPC)

In summary:

• API Gateway = managed API frontend (routing, auth, throttling, caching).
• Lambda = serverless backend logic (stateless, scales instantly).
• Together (AWS Lambda with API Gateway) they form the foundation of AWS serverless microservices.