AWS Lambda Function URLs Vs Amazon API Gateway. Which one services well for Your Application?

AWS Lambda Function URL and API Gateway are two ways to expose Lambda functions outside of AWS.

What is Amazon API Gateway?

Amazon API Gateway is an AWS service for creating REST, HTTP, and WebSocket APIs at any scale. API Gateway acts as the HTTPS endpoint URL when Amazon API Gateway, along with AWS Lambda, is used to build APIs.

To expose a lambda function via an HTTP endpoint, you must first create an API Gateway endpoint and then attach the lambda function. Setting it up properly required some knowledge of the API Gateway service and a few extra steps.

What is AWS Lambda Function URL?

A function URL is a dedicated HTTP(S) endpoint for your Lambda function.

Lambda function URLs make this process much easier. You can now quickly add a HTTPS endpoint by configuring your lambda function in the advanced settings section of the console.

This feature is useful for users who want to quickly set up HTTP URLs without having to worry about setting up an API Gateway endpoint.

Key Differences Between AWS Lambda Function URLs & Amazon API Gateway

1. API Gateway supports Caching, proxy to AWS services, WebSocket, Usage Plan, Manage API key & Access logs in CloudWatch, these are features not available in Lambda function URL.
2. API Gateway supports Custom Domain & Integration with AWS WAF. In Lambda function URL these are not supported directly we need to configure it manually with CloudFront.
3. API Gateway can validate Requests & Responses. But we can’t do it with the Lambda function URL. Also, it does not support Mapping but with API Gateway we can check Requests & Responses Mapping.
4. Lambda function URL can Authentication with IAM Role & NONE. And API Gateway Authentication with API key, IAM, Cognito, Lambda.
5. Lambda function URL response time is 15 minutes & API Gateway response time is 30 seconds only.

There is no extra cost to use Lambda function URL.

When can we use Lambda function URL?

• APIs Built with backend frameworks
• Webhooks handler
• Single function simple microservice.
• From validators
• Server-side website rendering
• Long-running big data processing
• Long polling cases

When can we use API Gateway?

• SaaS applications where need to track limit usage using API Gateway usage plans
• Real-time application using WebSockets
• Cases where API response time within 29 seconds
• Cases where required advance Authorization using Cognito, Throttling, Caching, Service proxy to other AWS services etc features required. 

This article provides an initial idea of an AWS Lambda function URL, so you can explore it later and use it in production scenarios.