Resolving Cloudfront and Multiple Lambda@ Edge Function Issues

Discover how to effectively use multiple `Lambda@ Edge` functions with `Cloudfront`, and troubleshoot common issues related to function triggering.
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This video is based on the question https://stackoverflow.com/q/63559778/ asked by the user 'Damien' ( https://stackoverflow.com/u/11612/ ) and on the answer https://stackoverflow.com/a/63709745/ provided by the user 'Damien' ( https://stackoverflow.com/u/11612/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Cloudfront and Lambda@ Edge Integration

Amazon Cloudfront is a rapid content delivery network (CDN) service provided by AWS. It speeds up the delivery of your applications and websites by routing requests to the closest edge location. A powerful feature of Cloudfront is its ability to integrate with Lambda@ Edge, which enables you to run serverless functions that can customize the content served by Cloudfront.

However, as some users discover, integrating multiple Lambda@ Edge functions can come with its own set of challenges. One common issue is when not all functions trigger as expected. In this guide, we'll explore troubleshooting a specific scenario where multiple Lambda@ Edge functions fail to trigger correctly in a Cloudfront distribution.

The Problem: Lambda@ Edge Functions Not Triggering

In the given situation, a user has set up a Cloudfront distribution with two Lambda@ Edge functions:

Viewer-Request Function: This function redirects users based on conditions set in the code.

Origin-Response Function: This function logs response statistics from the origin.

When the Cloudfront distribution domain is accessed, the viewer-request function triggers successfully, but the origin-response function does not. However, if the viewer-request function is removed, the origin-response function works as intended.

Potential Causes of the Issue

The main reason for the origin-response function not triggering while the viewer-request function is running could be related to the logic implemented in the viewer-request function or misunderstanding the flow of execution in AWS Lambda@ Edge.

The Solution: Adjusting the Code Logic

A user named Damien received helpful feedback suggesting a change to the code logic. Let's break down the recommended solution for better understanding.

Adjusting the Redirect Logic

Instead of performing the redirect in the viewer-request function, you can handle it within the origin-response function. This adjustment allows the server to complete the request flow before executing the redirection. Here's an improved approach:

Modify the Viewer-Request Function: Instead of directing users immediately, return a specific status or flag that indicates further processing is to be done.

[[See Video to Reveal this Text or Code Snippet]]

Implement the Redirect in the Origin-Response Function: Use the information from the viewer-request function to determine whether a redirect is necessary.

[[See Video to Reveal this Text or Code Snippet]]

Benefits of the Suggested Approach

Clear Separation of Duties: This approach separates the redirection logic from the initial request handling, streamlining the process.

Avoid Conflicts: Avoids conflicts between multiple Lambda triggers by clearly defining when a redirect should occur.

Logging Capability: Allows for robust logging and data collection within the origin-response function.

Conclusion

By reorganizing how redirections are handled between Lambda@ Edge functions, you can resolve issues of function triggering and maintain proper content delivery through Cloudfront. When implementing these functions, it's vital to understand how each function interacts within the request and response lifecycle to avoid unexpected behavior.

If you've encountered similar issues or would like further clarification on AWS services, feel free to reach out or leave a comment below.