connecting-lambda-to-api-gateway

Create a REST API with aws apigateway create-rest-api, add a resource and method, then configure an AWS_PROXY integration pointing to the Lambda function ARN. Finally, grant apigateway.amazonaws.com invoke permission and deploy the API to a stage.

Create an OPTIONS method with a MOCK integration and add Access-Control-Allow-Origin, Access-Control-Allow-Headers, and Access-Control-Allow-Methods headers in both method and integration responses. Your Lambda function should also return CORS headers in its response.

A 502 usually means the Lambda response is not proxy-compatible. The function must return an object with statusCode, headers, and a stringified body field; returning a raw object as body causes a malformed response error.

API Gateway supports AWS_IAM, COGNITO_USER_POOLS, CUSTOM authorizers, and NONE. For production, avoid NONE and combine IAM or Cognito authorization with API keys, throttling usage plans, and access logging.

API Gateway needs an explicit lambda:InvokeFunction permission added via aws lambda add-permission with principal apigateway.amazonaws.com. The source ARN must match the API Gateway execution ARN for your API, stage, and method.