See the following examples to use Lambda functions with Amazon CloudFront.

General examples

The following examples show common ways to use Lambda@Edge in CloudFront.

Example: A/B testing

You can use the following example to test two different versions of an image without creating redirects or changing the URL. This example reads the cookies in the viewer request and modifies the request URL accordingly. If the viewer doesn't send a cookie with one of the expected values, the example randomly assigns the viewer to one of the URLs.

The following example shows how to change the value of a response header based on the value of another header.

Generate responses - examples

The following examples show how you can use Lambda@Edge to generate responses.

Example: Serve static content (generated response)

The following example shows how to use a Lambda function to serve static website content, which reduces the load on the origin server and reduces overall latency.

Example: Generate an HTTP redirect (generated response)

The following example shows how to generate an HTTP redirect.

Query strings - examples

The following examples show ways that you can use Lambda@Edge with query strings.

The following example shows how to get the key-value pair of a query string parameter, and then add a header based on those values.

Example: Normalize query string parameters to improve the cache hit ratio

The following example shows how to improve your cache hit ratio by making the following changes to query strings before CloudFront forwards requests to your origin:

For more information, see Cache content based on query string parameters.

Example: Redirect unauthenticated users to a sign-in page

The following example shows how to redirect users to a sign-in page if they haven't entered their credentials.

Personalize content by country or device type headers - examples

The following examples show how you can use Lambda@Edge to customize behavior based on location or the type of device used by the viewer.

Example: Redirect viewer requests to a country-specific URL

The following example shows how to generate an HTTP redirect response with a country-specific URL and return the response to the viewer. This is useful when you want to provide country-specific responses. For example:

Note the following:

Example: Serve different versions of an object based on the device

The following example shows how to serve different versions of an object based on the type of device that the user is using, for example, a mobile device or a tablet. Note the following:

Content-based dynamic origin selection - examples

The following examples show how you can use Lambda@Edge to route to different origins based on information in the request.

Example: Use an origin request trigger to change from a custom origin to an Amazon S3 origin

This function demonstrates how an origin-request trigger can be used to change from a custom origin to an Amazon S3 origin from which the content is fetched, based on request properties.

Example: Use an origin-request trigger to change the Amazon S3 origin Region

This function demonstrates how an origin-request trigger can be used to change the Amazon S3 origin from which the content is fetched, based on request properties.

In this example, we use the value of the CloudFront-Viewer-Country header to update the S3 bucket domain name to a bucket in a Region that is closer to the viewer. This can be useful in several ways:

To use this example, you must do the following:

Example: Use an origin request trigger to change from an Amazon S3 origin to a custom origin

This function demonstrates how an origin-request trigger can be used to change the custom origin from which the content is fetched, based on request properties.

Example: Use an origin request trigger to gradually transfer traffic from one Amazon S3 bucket to another

This function demonstrates how you can gradually transfer traffic from one Amazon S3 bucket to another in a controlled way.

Example: Use an origin request trigger to change the origin domain name based on the country header

This function demonstrates how you can change the origin domain name based on the CloudFront-Viewer-Country header, so content is served from an origin closer to the viewer's country.

Implementing this functionality for your distribution can have advantages such as the following:

Note that to enable this functionality you must configure your distribution to cache based on the CloudFront-Viewer-Country header. For more information, see Cache based on selected request headers.

Update error statuses - examples

The following examples provide guidance for how you can use Lambda@Edge to change the error status that is returned to users.

Example: Use an origin response trigger to update the error status code to 200

This function demonstrates how you can update the response status to 200 and generate static body content to return to the viewer in the following scenario:

Example: Use an origin response trigger to update the error status code to 302

This function demonstrates how you can update the HTTP status code to 302 to redirect to another path (cache behavior) that has a different origin configured. Note the following:

Access the request body - examples

The following examples show how you can use Lambda@Edge to work with POST requests.

Example: Use a request trigger to read an HTML form

This function demonstrates how you can process the body of a POST request generated by an HTML form (web form), such as a "contact us" form. For example, you might have an HTML form like the following:

<html>
  <form action="https://example.com" method="post">
    Param 1: <input type="text" name="name1"><br>
    Param 2: <input type="text" name="name2"><br>
    input type="submit" value="Submit">
  </form>
</html>

For the example function that follows, the function must be triggered in a CloudFront viewer request or origin request.

Example: Use a request trigger to modify an HTML form

This function demonstrates how you can modify the body of a POST request generated by an HTML form (web form). The function is triggered in a CloudFront viewer request or origin request.