AWS API Gateway

AWS API Gateway

Amazon API Gateway is a fully managed service for creating, deploying, and managing APIs at any scale. It allows developers to create RESTful APIs, WebSocket APIs, and HTTP APIs to connect front-end applications to back-end services or resources. API Gateway acts as a gateway for incoming API requests, performing tasks such as traffic management, authorization, access control, monitoring, and API versioning.

Key Concepts of AWS API Gateway

  1. What is AWS API Gateway?
    • AWS API Gateway is a fully managed service that allows you to create and manage APIs for your backend services, such as AWS Lambda, EC2, or other HTTP services.
    • It helps in defining RESTful APIs, WebSocket APIs, and HTTP APIs.
  2. API Types in API Gateway:
    • REST APIs: Standard RESTful APIs for CRUD operations using HTTP methods (GET, POST, PUT, DELETE).
    • WebSocket APIs: For building real-time, two-way communication applications like chat or live updates.
    • HTTP APIs: A lightweight version of REST APIs, optimized for low-latency use cases with fewer features.
  3. Core Components:
    • Resources: Represents an endpoint, such as /users or /orders.
    • Methods: The HTTP operations for a resource (e.g., GET, POST).
    • Stages: Deployment environments like dev, test, prod.
    • Models: Define the structure of the input and output data (e.g., request/response formats).
    • API Keys: Used for metering and rate-limiting API usage.
    • Lambda Integration: API Gateway can forward requests to AWS Lambda functions to handle backend logic.
  4. API Gateway Features:
    • Request and Response Transformation: Modify requests before forwarding to backend and modify responses before sending to the client.
    • CORS: Cross-Origin Resource Sharing (CORS) for enabling front-end applications hosted on different domains to make API calls.
    • Authorization and Access Control: API Gateway supports multiple authorization mechanisms such as AWS IAM roles, Amazon Cognito user pools, and custom authorizers (Lambda functions).
    • Throttling and Rate Limiting: API Gateway allows you to set request limits to prevent abuse and protect backend services.
    • Caching: You can cache API responses to improve performance and reduce latency.
    • Logging and Monitoring: AWS CloudWatch integration for logging requests and monitoring metrics.

AWS API Gateway Architecture

  1. Request Flow:
    • Client sends request to API Gateway.
    • API Gateway processes request (authentication, authorization, request transformation, throttling).
    • API Gateway forwards request to backend (Lambda function, EC2, or HTTP endpoint).
    • Backend processes the request and returns a response.
    • API Gateway returns response to the client (response transformation, CORS, etc.).
  2. Integration Types:
    • Lambda Proxy Integration: API Gateway forwards the entire request (headers, body, query parameters) to Lambda, and Lambda returns a formatted response.
    • Lambda Non-Proxy Integration: API Gateway sends only the body or selected fields to Lambda. You define how to handle requests and responses.
    • HTTP Proxy Integration: API Gateway acts as a proxy and forwards the request directly to an HTTP endpoint without any transformation.
    • Mock Integration: Used for testing or when you want API Gateway to respond with static data without forwarding the request to a backend.

API Gateway Security

  1. Authorization Methods:
    • AWS IAM: Use IAM roles and policies to grant access to APIs (useful for internal services).
    • Amazon Cognito: Use Amazon Cognito User Pools for user authentication and access control, often used for apps requiring user login.
    • Lambda Authorizers (Custom Authorizers): Use a Lambda function to authorize API requests, providing full flexibility for complex authorization logic.
    • API Keys: API Gateway can validate requests using API keys for access control and usage metering.
  2. Encryption:
    • Data in Transit: API Gateway automatically uses TLS for all connections, encrypting data between the client and the service.
    • Data at Rest: You can configure API Gateway to encrypt data stored in CloudWatch logs or other associated AWS services using AWS KMS (Key Management Service).
  3. CORS (Cross-Origin Resource Sharing):
    • CORS enables clients (often JavaScript running in a browser) to make API calls to a domain other than the one from which the client was loaded.
    • API Gateway simplifies the process of enabling CORS by providing a configuration setting to automatically include the correct headers in responses.

API Gateway Monitoring and Logging

  1. CloudWatch Metrics:
    • API Gateway provides metrics such as:
      • Count: The number of requests.
      • 4XX/5XX Errors: The number of client/server errors.
      • Latency: The time taken to process requests.
      • Integration Latency: Time spent in the backend service.
  2. CloudWatch Logs:
    • You can enable logging to track API request and response details. This is useful for debugging and monitoring purposes.
    • Access Logging: Logs HTTP request information (headers, query parameters, etc.).
    • Execution Logging: Logs API Gateway execution details such as integration calls, transformations, and Lambda invocations.
  3. X-Ray:
    • AWS X-Ray can trace the entire lifecycle of requests from the API Gateway through backend services like Lambda, EC2, or RDS, providing deep insights into performance bottlenecks.

API Gateway Caching

  1. Cache Responses:
    • API Gateway can cache responses to reduce backend load and improve performance.
    • Cache can be set at the method level, with options to specify TTL (Time-to-Live) for cached responses.
    • API Gateway provides cache invalidation if backend data changes.
  2. When to Use Caching:
    • Caching is useful when the API response is consistent and doesn’t change frequently (e.g., reference data, configuration).
    • It reduces the load on backend services and improves the response time for end users.

API Gateway Pricing

  1. Request Charges:
    • Charges are based on the number of requests processed by the API Gateway.
    • The first 1 million requests per month are free, with subsequent requests charged based on the request type (REST, HTTP, WebSocket).
  2. Data Transfer Costs:
    • Data transfer out of API Gateway is charged by the amount of data transferred, but data transfer between API Gateway and other AWS services (like Lambda, EC2) is free.
  3. Additional Charges:
    • Cache: Caching incurs additional charges based on the amount of cache memory allocated.
    • Custom Domain Names: If you use custom domain names for your API, you’ll incur additional charges.

Best Practices

  1. Designing REST APIs:
    • Follow RESTful design principles: use proper HTTP methods (GET for reading, POST for creating, PUT for updating, DELETE for removing).
    • Use versioning in the URL (e.g., /v1/ or /v2/) to handle changes without breaking existing clients.
  2. Minimize Latency:
    • Use Lambda Proxy Integration to directly forward requests and reduce processing time.
    • Enable API Gateway Caching to reduce latency for repetitive requests.
  3. Error Handling:
    • Configure custom error responses to handle different HTTP error codes (e.g., 400 for bad requests, 401 for unauthorized access).
    • Use Lambda functions for custom error handling or to manipulate error messages before returning to the client.
  4. Enable Monitoring and Logging:
    • Always enable CloudWatch logs for visibility into API usage and to debug errors quickly.
    • Use X-Ray tracing to monitor the end-to-end performance of API calls, especially when using multiple AWS services.
  5. API Throttling:
    • Use API Gateway’s rate limiting and throttling features to prevent overloading backend systems, especially if you have high request volumes.

Common Interview Questions

  1. What is AWS API Gateway, and why would you use it?
    • API Gateway is a managed service that simplifies the creation, deployment, and management of APIs. It acts as a reverse proxy to backend services and supports authentication, authorization, and traffic management.
  2. What is the difference between REST APIs, HTTP APIs, and WebSocket APIs in API Gateway?
    • REST APIs: Traditional RESTful APIs, suited for most CRUD operations.
    • HTTP APIs: Lightweight, lower-latency APIs for simple use cases with fewer features.
    • WebSocket APIs: For real-time communication applications that require bi-directional communication.
  3. How can you secure APIs in AWS API Gateway?
    • Secure APIs using IAM roles, Amazon Cognito User Pools, Lambda Authorizers, and API Keys. Use TLS to secure data in transit and enable CloudWatch Logs to monitor access.
  4. How can you enable CORS in API Gateway?
    • CORS (Cross-Origin Resource Sharing) can be enabled in API Gateway by configuring it in the method settings, specifying allowed origins, methods, and headers for cross-domain requests.
  5. **Explain API Gateway’s rate limiting and throttling capabilities.**
  • API Gateway allows you to define throttling settings (requests per second) to limit the number of requests sent to backend services. This helps protect your services from excessive load and abuse.

This cheat sheet should give you a solid understanding of AWS API Gateway, its components, and best practices for using it effectively.

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