Apache ProxyPass Based on Request URI Length

Question

I've got a problem with Apache ProxyPass (more specifically ProxyPassMatch) where I'm trying to proxy https://domain.com/ {6 character key} to another server.

I've tried regex's like the following (attempting to take into consideration multiple ways that this might be handled by Apache):

ProxyPassMatch "/^.{22,22}$/g" https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{7,7}$/g"   https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{14,14}$/g" https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{23,23}$/g" https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{21,21}$/g" https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{8,8}$/g"   https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{6,6}$/g"   https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{15,15}$/g" https://domain.com/api/{6 character key}
ProxyPassMatch "/^.{13,13}$/g" https://domain.com/api/{6 character key}

However nothing seems to work. Any help on this matter would be greatly appreciated.

Answer 1

The fix

You need to capture the characters in the pattern and then reference them in the url:

Example from the docs:

ProxyPassMatch "^/(.*\.gif)$" "http://backend.example.com/$1"

https://httpd.apache.org/docs/2.4/mod/mod_proxy.html#proxypassmatch

So in your case I think what you want is:

ProxyPassMatch "/^(.{6})$/"   "https://domain.com/api/$1"

Why/How this works

When using regular expressions, you can capture matched text by using brackets and then reference them using $1 for the first set of brackets, $2 for the second etc.

eg

   ProxyPassMatch "/^(.{6})/(.{6})$/"   "https://domain.com/api/$2/$1"

Would match http://domain.com/123456/ABCDEF and proxy to https://domain.com/api/ABCDEF/123456

One more thing

Also note you don't need {6,6} and can just use {6} to say you need the character to match exactly 6 times, you use this format where you want a variable number of characters eg {4,6} for between 4 and 6 - you can also specify {4,} for 4 or more.