Understanding the basics of Lambda Function URLs

Published: October 21, 2023 | Modified: October 21, 2023

In this guide, we’ll take you through the fundamental concepts of Lambda Function URLs. We’ll discuss their definition, explore their applications, and address security considerations, providing a comprehensive overview.

What is the Lambda Function URL?

It’s a dedicated, unique, and static URL for your Lambda function, enabling remote invocation of the backend Lambda function over the network call. This straightforward and budget-friendly method simplifies Lambda function invocation, bypassing the need for managing complex front-end infrastructure like API Gateway, Load Balancers, or CloudFront. However, this comes at the expense of advanced features provided by these services.

It follows the format:

https://<url-id>.lambda-url.<region>.on.aws

Why to use Lambda Fuction URL?

• Creating them is quite straightforward and simple. The AuthType (security) is the only configuration you need to provide. CORS config is optional.
• They come at no additional cost.
• Once configured, they require minimal maintenance.
• For straightforward use cases, they can replace the need for designing, managing, and incurring the costs of front-end infrastructure, such as API Gateway.
• They are most appropriate for development scenarios where you can prioritize other aspects of applications/architecture over the complexity of Lambda invocation methods.

When to use Lambda Function URLs?

Lambda Function URLs serve a valuable role in accelerating the testing and development of the application, by prioritizing Lambda invocations in the application’s progress, while the method of invocation takes a backseat.

In production, they’re practical when your design doesn’t necessitate the advanced features provided by alternative invocation methods like API Gateway or Load Balancers, etc.

These URLs are also beneficial when dealing with a limited number of Lambdas, offering a simple, cost-effective, and maintenance-free approach to invocations.

How to secure Lambda Function URLs?

You can manage access to Lambda Function URLs by specifying the AuthType, which offers two configurable options:

1. AWS_IAM: This allows you to define AWS entities (users or roles) that are granted access to the function URL. You need to ensure a proper resource policy is in place allowing intended entities access to Action: lambda:InvokeFunctionUrl
2. NONE: Provides public, unauthenticated access. Use this option cautiously, as it allows unrestricted access. When you choose this option, Lambda automatically creates a resource-based policy with Principal: * and Action: lambda:InvokeFunctionUrl and attaches to function.

It’s important to remember that Lambda’s resource-based policy is always enforced in conjunction with the selected AuthType. Please read this AWS documentation for more details.

The Lambda resource policy can be configured at Lambda > Configuration > Permissions > Resource-based policy statements.

With the basics of Lambda Function URLs in mind, refer to how to create Lambda Function URL and kick-start your journey with them!