What is API Gateway?

API Gateway is a fully managed service that allows you to create, publish, maintain, and secure APIs for interacting with backend services like AWS Lambda, EC2, or external endpoints. It serves as an entry point for client requests to Lambda functions.

Key Features of API Gateway with Lambda

1. Integration with Lambda
   • API Gateway seamlessly triggers Lambda functions based on HTTP/HTTPS requests from clients.
   • It manages the communication, mapping request payloads to Lambda inputs and vice versa.
2. Request Transformation
   • API Gateway can map client requests into a format required by Lambda, including modifying headers, query parameters, or body content.
   • Responses from Lambda can also be transformed before reaching the client.
3. Security
   • Supports AWS IAM Roles, API Keys, Cognito User Pools, and Lambda Authorizers for securing APIs.
   • Integrates with AWS WAF (Web Application Firewall) for protection against threats.
4. Rate Limiting & Throttling
   • API Gateway offers throttling and rate-limiting to control traffic and prevent overloading backend services like Lambda.
5. Caching
   • Supports response caching to reduce repeated Lambda invocations and improve performance for common requests.
6. Monitoring
   • Detailed metrics and logs are available via Amazon CloudWatch, including request/response counts, errors, and latency.

Steps to Set Up API Gateway for a Lambda Function

1. Create a Lambda Function
   • Develop a Lambda function in your preferred runtime.
   • Test the function directly using the Lambda console.
2. Set Up an API Gateway
   • Navigate to the API Gateway console.
   • Create an HTTP API or REST API (depending on the requirements).
   • Define resources and methods (e.g., GET, POST).
3. Integrate with Lambda
   • For each method, set the integration type to "Lambda Function."
   • Specify the Lambda function name.
   • Grant API Gateway permission to invoke the Lambda function using an AWS-managed policy.
4. Deploy the API
   • Deploy the API to a specific stage (e.g., dev, prod).
   • Use the stage URL as the API endpoint.
5. Test the API
   • Use tools like Postman, cURL, or browser to send requests to the API Gateway endpoint.

Best Practices

1. Optimize Payload Size
   • Keep request and response payloads as small as possible to reduce latency.