Choosing between CloudFront Functions and Lambda@Edge - Amazon CloudFront

Choosing between CloudFront Functions and Lambda@Edge

CloudFront Functions and Lambda@Edge both provide a way to run code in response to CloudFront events. However, there are important differences that distinguish them. These differences can help you choose the one that’s right for your use case. The following table lists some of the important differences between CloudFront Functions and Lambda@Edge.

CloudFront Functions Lambda@Edge
Programming languages JavaScript (ECMAScript 5.1 compliant) Node.js and Python
Event sources
  • Viewer request

  • Viewer response

  • Viewer request

  • Viewer response

  • Origin request

  • Origin response

Scale 10,000,000 requests per second or more Up to 10,000 requests per second per Region
Function duration Submillisecond

Up to 5 seconds (viewer request and viewer response)

Up to 30 seconds (origin request and origin response)

Maximum memory 2 MB 128 – 3,008 MB
Maximum size of the function code and included libraries 10 KB

1 MB (viewer request and viewer response)

50 MB (origin request and origin response)

Network access No Yes
File system access No Yes
Access to the request body No Yes
Access to geolocation and device data Yes

No (viewer request)

Yes (origin request, origin response, and viewer response)

Can build and test entirely within CloudFront Yes No
Function logging and metrics Yes Yes
Pricing Free tier available; charged per request No free tier; charged per request and function duration

CloudFront Functions is ideal for lightweight, short-running functions for use cases like the following:

  • Cache key normalization – You can transform HTTP request attributes (headers, query strings, cookies, and even the URL path) to create an optimal cache key, which can improve your cache hit ratio.

  • Header manipulation – You can insert, modify, or delete HTTP headers in the request or response. For example, you can add a True-Client-IP header to every request.

  • URL redirects or rewrites – You can redirect viewers to other pages based on information in the request, or rewrite all requests from one path to another.

  • Request authorization – You can validate hashed authorization tokens, such as JSON web tokens (JWT), by inspecting authorization headers or other request metadata.

To get started with CloudFront Functions, see Customizing at the edge with CloudFront Functions.

Lambda@Edge is a good fit for the following scenarios:

  • Functions that take several milliseconds or more to complete.

  • Functions that require adjustable CPU or memory.

  • Functions that depend on third-party libraries (including the AWS SDK, for integration with other AWS services).

  • Functions that require network access to use external services for processing.

  • Functions that require file system access or access to the body of HTTP requests.

To get started with Lambda@Edge, see Customizing at the edge with Lambda@Edge.