I've a REST API application running in two EC2 instance and was using AWS Classic Load Balancer for a long time. The clients of REST API rely on the response headers (e.g. such as Location).
I know that HTTP headers are case-insensitive by definition, however (unfortunately) some clients are ignoring this and checking the headers in a case-sensitive way (e.g. they expect Location to start with upper case).
Recently I've changed to AWS Application Load Balancer and now I see that it transforms all response headers to lower case, as a result clients are failing to handle the response properly.
I've couple of questions here.
- Is it expected behavior of Application Load Balancer?
- Is there a way to configure it to return headers as they have been built by the application?
It is an expected function of the ALB because HTTP/2 lowercases all headers and ALBs support HTTP/2. Unfortunately you can't modify how the headers are manipulated by the ALB.
Update: See the comments below. My statement that the ALB lowercases the request headers due to its support for HTTP/2 may not be accurate.
This was causing our broken clients to fail when we switched from TCP ELB to HTTPS ELB.
While we fix our clients, we temporarily disabled the new ELB HTTP/2 support, which comes enabled by default.
来源：https://stackoverflow.com/questions/39871250/aws-application-load-balancer-transforms-all-headers-to-lower-case