Understanding the basics of Lambda Function URLs

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!