I want to allow underscore( _ ) https header in load balancer

Hi there,

I understand that you want to know if there a way to override the "Drop Invalid header fields" ALB attribute to allow headers containing Underscore in them.

Unfortunately, there is no current ability for the ALB to consider underscore character as valid, and thus no option will be able to override this attribute if routing.http.drop_invalid_header_fields.enabled is set to true.

Although there is a workaround which will allow you to pass the headers with underscores.

You can set routing.http.drop_invalid_header_fields.enabled to false and ensure routing.http.desync_mitigation_mode is in DEFENSIVE mode.

The only limitation here is that, it allows invalid headers to pass, while desync_mitigation_mode ensures desync suspected requests doesn't share connection.

Desync mitigation is invented by ELB and goal is to protect weak target servers and underscore character is one of them that leads to confusion to some target servers that we protect.

Kind Regards,

Ahmad