HAProxy: hdr_dom(host) with redirects - haproxy

Question

We have a couple of haproxy configurations running fine for the most part.
In our scenario, we simply route requests based on domain names.
Here a sample for one domain, drawmessage.com:
frontend http
bind *:80
redirect prefix http://app.drawmessage.com code 301 if { hdr_dom(host) -i www.app.drawmessage.com }
redirect prefix http://drawmessage.com code 301 if { hdr_dom(host) -i www.drawmessage.com }
redirect prefix https://drawmessage.com code 301 if { hdr_dom(host) -i drawmessage.com }
use_backend http:app.drawmessage.com if { hdr_dom(host) -i app.drawmessage.com }
use_backend http:app.drawmessage.com if { hdr_dom(host) -i app-drawmessage-com.d250.hu }
use_backend http:drawmessage.com if { hdr_dom(host) -i drawmessage.com }
use_backend http:drawmessage.com if { hdr_dom(host) -i drawmessage-com.d250.hu }
There are other domains also, this is filtered for this domain only. As you can see, after redirects for www, we apply a special redirect for drawmessage.com, but theoretically not for app.drawmessage.com.
frontend https
bind *:443 ssl crt /var/haproxy
redirect prefix https://app.drawmessage.com code 301 if { hdr_dom(host) -i www.app.drawmessage.com }
redirect prefix https://drawmessage.com code 301 if { hdr_dom(host) -i www.drawmessage.com }
use_backend https:app.drawmessage.com if { hdr_dom(host) -i app.drawmessage.com }
use_backend https:app.drawmessage.com if { hdr_dom(host) -i app-drawmessage-com.d250.hu }
use_backend https:drawmessage.com if { hdr_dom(host) -i drawmessage.com }
use_backend https:drawmessage.com if { hdr_dom(host) -i drawmessage-com.d250.hu }
The problem is that actually, we do not want a redirect to https for the subdomain app.drawmessage.com, but since we have a redirect for the domain the redirect rule applies for both. Reordering the rules in a way, so that the sorting matches the configuration we want to achieve does produce the same result, and we get haproxy warnings:
a 'redirect' rule placed after a 'use_backend' rule will still be processed before.
If the order of configuration lines affects the order of processing a request, thus the ordering is a configuration parameter itself, why are redirect rules processed before use_backend rules? ...
Anyone has a suggestion how to achieve domain-based routing, with the correct preference of redirects? I would prefer a clean and simple way, ..

Answer 1

Don't use hdr_dom(). Just use hdr().
redirect prefix https://drawmessage.com code 301 if { hdr(host) -i drawmessage.com }
The _dom suffix means you want to match the value given later against any number of complete, consecutive domain-name-like tokens found in the specified header, so the pattern you provide must begin either at the beginning of the string or immediately following a . and must end either at the end of the string or be immediately followed by a .. That isn't what you want to do, so hdr_dom() isn't the correct fetch to use.
The notation may imply that you are comparing left value against right value, but the comparison is actually right value against left value.
a 'redirect' rule placed after a 'use_backend' rule will still be processed before because these directives are handled by different parts of the HAProxy code, at different stages of request processing. Within each class of rule, the order is preserved, but redirects are handled near the beginning and backend selection is near the end of request processing.