Launch Announcement - New ALB enhancements provide options to specify how to process Host header and X-Forwarded-For header

We are happy to announce that we just launched two enhancements to define how the Application Load Balancer (ALB) will process Host header and X-Forwarded-For header. These options provide additional flexibility in handling HTTP/HTTPS requests and allow customers to migrate their workloads to ALB.

Background: AWS customers had asked for flexibility in specifying how ALB would handle Host and X-Forwarded-For headers in HTTP/HTTPS Requests. The enhancements are as follows:

Host Header Enhancement:

• Currently, ALB modifies Host header in the incoming HTTP/HTTPS Request, and appends listener port before sending it to targets. For example, the Host: www.amazon.com header in the HTTP Request is modified to Host: www.amazon.com:8443 before ALB sends it to targets. This will remain the default behavior for backward compatibility.
• With this enhancement, when enabled using a new attribute, ALB will send the Host header without any modification to the target. For example, the Host: www.amazon.com header in the HTTP Request will not be modified and sent to target as is.

X-Forwarded-For Header Enhancement:

• Currently, ALB appends IP address of the previous hop to the X-Forwarded-For header before forwarding it to targets. This will remain the default behavior for backward compatibility.
• With this enhancement, customers can now specify whether the ALB should preserve or delete the X-Forwarded-For header before sending it to the targets.

Launch Details:

• Both enhancements do not change the default behavior and existing ALBs are not affected.
• The enhancements are available using API and AWS Console.
• The enhancements are available in all commercial, GovCloud, and China regions. These will be deployed in ADC regions at a later date based on demand.

Launch Materials:

• Documentation for Host header enhancement - https://docs.aws.amazon.com/elasticloadbalancing/latest/application/application-load-balancers.html#host-header-preservation
• Documentation for X-Forwarded-For header enhancement - https://docs.aws.amazon.com/elasticloadbalancing/latest/application/x-forwarded-headers.html#x-forwarded-for

Please give these enhancement a try.

Thank you.