AwsHow-ToBeginner · 4 min read

How to Integrate API Gateway with Lambda in AWS

To integrate API Gateway with Lambda, create an API Gateway REST API or HTTP API and configure a method or route to trigger your Lambda function. This setup allows API Gateway to invoke Lambda when an HTTP request is received, enabling serverless backend logic.

📐

Syntax

The integration involves these parts:

API Gateway API: Defines the HTTP endpoint.
Resource and Method (REST API) or Route (HTTP API): Specifies the URL path and HTTP method (GET, POST, etc.).
Integration: Connects the method or route to the Lambda function.
Lambda Function: The backend code executed on request.

API Gateway forwards the request to Lambda and returns Lambda's response to the client.

bash

aws apigateway create-rest-api --name "MyAPI"
aws apigateway create-resource --rest-api-id <api-id> --parent-id <root-id> --path-part "mypath"
aws apigateway put-method --rest-api-id <api-id> --resource-id <resource-id> --http-method GET --authorization-type NONE
aws apigateway put-integration --rest-api-id <api-id> --resource-id <resource-id> --http-method GET --type AWS_PROXY --integration-http-method POST --uri arn:aws:apigateway:<region>:lambda:path/2015-03-31/functions/<lambda-arn>/invocations
aws lambda add-permission --function-name <lambda-name> --statement-id apigateway-access --action lambda:InvokeFunction --principal apigateway.amazonaws.com --source-arn arn:aws:execute-api:<region>:<account-id>:<api-id>/*/GET/mypath

💻

Example

This example shows how to create a simple HTTP API in AWS Console that triggers a Lambda function on GET requests to /hello.

The Lambda function returns a JSON greeting.

python

import json

def lambda_handler(event, context):
    return {
        'statusCode': 200,
        'headers': {'Content-Type': 'application/json'},
        'body': json.dumps({'message': 'Hello from Lambda!'})
    }

Output

{"message": "Hello from Lambda!"}

⚠️

Common Pitfalls

Missing Lambda permission: API Gateway must have permission to invoke Lambda. Use lambda add-permission.
Wrong integration type: Use AWS_PROXY for Lambda proxy integration to pass request details.
Incorrect URI format: The Lambda ARN in API Gateway integration URI must be exact.
Not deploying API: After changes, deploy the API to a stage to make it live.

bash

Wrong:
aws apigateway put-integration --rest-api-id <api-id> --resource-id <resource-id> --http-method GET --type AWS --integration-http-method POST --uri arn:aws:lambda:<region>:<account-id>:function:<lambda-name>

Right:
aws apigateway put-integration --rest-api-id <api-id> --resource-id <resource-id> --http-method GET --type AWS_PROXY --integration-http-method POST --uri arn:aws:apigateway:<region>:lambda:path/2015-03-31/functions/arn:aws:lambda:<region>:<account-id>:function:<lambda-name>/invocations

📊

Quick Reference

Remember these key steps:

Create API Gateway API and resource.
Set method and integration type to AWS_PROXY.
Use correct Lambda ARN format in integration URI.
Grant API Gateway permission to invoke Lambda.
Deploy API to a stage before testing.

✅

Key Takeaways

Use AWS_PROXY integration type for full Lambda request and response handling.

Grant API Gateway permission to invoke your Lambda function explicitly.

Deploy your API Gateway changes to a stage to make them active.

Ensure the Lambda ARN in the integration URI is correctly formatted.

Test your API endpoint after deployment to verify Lambda integration.