# Differences between CloudFront Functions and Lambda@Edge
<a name="edge-functions-choosing"></a>

CloudFront Functions and Lambda@Edge both provide a way to run code in response to CloudFront events. 

CloudFront Functions is ideal for lightweight, short-running functions for the following use cases:
+ **Cache key normalization** – Transform HTTP request attributes (headers, query strings, cookies, and even the URL path) to create an optimal [cache key](understanding-the-cache-key.md), which can improve your cache hit ratio.
+ **Header manipulation** – 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** – Redirect viewers to other pages based on information in the request, or rewrite all requests from one path to another.
+ **Request authorization** – 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 [Customize at the edge with CloudFront Functions](cloudfront-functions.md).

Lambda@Edge is ideal for the following use cases:
+ 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 [Customize at the edge with Lambda@Edge](lambda-at-the-edge.md).

To help you choose the option for your use case, use the following table to understand the differences between CloudFront Functions and Lambda@Edge. For information about differences that apply for origin modification helper methods, see [Choose between CloudFront Functions and Lambda@Edge](helper-functions-origin-modification.md#origin-modification-considerations).


|  | CloudFront Functions | Lambda@Edge | 
| --- | --- | --- | 
| Programming languages | JavaScript (ECMAScript 5.1 compliant) | Node.js and Python | 
| Event sources |  [\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/edge-functions-choosing.html)  |  [\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/edge-functions-choosing.html)  | 
|  Supports [Amazon CloudFront KeyValueStore](kvs-with-functions.md)  |  Yes CloudFront KeyValueStore only supports [JavaScript runtime 2.0](functions-javascript-runtime-20.md)  |  No  | 
| Scale | Up to millions of requests per second | Up to 10,000 requests per second per Region | 
| Function duration | Submillisecond |  Up to 30 seconds (viewer request and viewer response) Up to 30 seconds (origin request and origin response)  | 
|  Maximum function memory size  | 2 MB |  128 MB (viewer request and viewer response) 10,240 MB (10 GB) (origin request and origin response) For more information, see [Quotas on Lambda@Edge](cloudfront-limits.md#limits-lambda-at-edge).  | 
| Maximum size of the function code and included libraries | 10 KB |  50 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 and viewer response) Yes (origin request and origin response)  | 
| Can build and test entirely within CloudFront | Yes | No | 
| Function logging and metrics | Yes | Yes |