Options for X-Forwarded-For header with Cloudfront-ELB-Haproxy flow

Question

A customer is implementing Cloudfront with ELB and HAProxy on EC2. They are also evaluating AWS WAF for protecting App Traffic but because of application requirements they may not be able to move to ALB and hence cant work with WAF for this workload.

They are looking at implementing Access Control at HAProxy layer. But have expressed concerns around reliability of X-Forwarded-For headers as reliable source to implement it. I wanted to seek expert thoughts on better alternatives to help them implement this.

Accepted Answer

Yes. X-Forwarded-For Header can be manipulate.   
So, You can use Lambda@Edge for origin request phase to overwrite X-Forwarded-For header or create other header like True-Client-IP.

Simple example is below.

```
'use strict';

exports.handler = function(event, context, callback) {  
  var request = event.Records[0].cf.request;  
  request.headers["true-client-ip"] = [{"key":"True-Client-IP","value":request.clientIp}]   
  request.headers["x-forwarded-for"] = [{"key":"X-Forwarded-For","value":request.clientIp}]

callback(null, request);  
};
```

please check other L@E samples  below.
https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-examples.html

Options for X-Forwarded-For header with Cloudfront->ELB->Haproxy flow

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