LiteSpeed ADC Advanced Reverse Proxy Usage

In previous basic configuration wiki it explains how to set up a basic reverse proxy, but in that case the request URI needed to be the same in the frontend as the backend, otherwise a 404 Not Found Error would be returned.

In this guide we will give examples for more advanced reverse proxy usage for two scenarios: proxy a frontend URI to different backend URI, or mask the URI.

We will use 3 test servers as example , each of them has domain

adc.litespeed.dev

adc2.litespeed.dev

adc3.litespeed.dev

respectively , and adc.litespeed.dev will be the main server and other two are served for different backend

with each server, we create a php file with code:

<?php
echo "SCRIPT_FILENAME: ".$_SERVER["SCRIPT_FILENAME"]."<br>" ;
echo "SERVER ADDR: ".$_SERVER["SERVER_ADDR"]."<br>";
echo "HTTP_HOST: ".$_SERVER['HTTP_HOST']."<br>";

This allows us to determine which backend and what file we are requesting with.

We have also created 3 cluster backend to match each domain to its real IP, because ADC will redirect/proxy the request to cluster worker to do the proxy.

We have two methods to do this, via RewriteRule or Context

In ADC Virtual host ---> RewriteRule tab , enable rewrite rule and add rule:

RewriteRule ^(.*)$ http://adc2/$1 [P,E=Proxy-Host:adc2.litespeed.dev]

where adc2 is the cluster name , and adc2.litespeed.dev is backend domain , otherwise you may get 404 error if hostname doesn't match in backend.

Now save and restart ADC , check the page again , you will see it is proxied to adc2.litespeed.dev

Now we can use RewriteCond and RewriteRule to further customize it

For example we want to proxy request URI that contains string adc2 to adc2.litespeed.dev and URI contains adc3 to adc3.litespeed.dev

Ruleset:

RewriteCond %{QUERY_STRING} adc2
RewriteRule ^(.*)$ http://adc2/$1 [P,E=Proxy-Host:adc2.litespeed.dev,L]

RewriteCond %{QUERY_STRING} adc3
RewriteRule ^(.*)$ http://adc3/$1 [P,E=Proxy-Host:adc3.litespeed.dev,L]

Result:

We can also rewrite the URL , we create a file new-uri.php with same PHP code , this time we will rewrite adc.litespeed.dev/index.php?rewrite to adc3.litespeed.dev/new-uri.php

Ruleset:

RewriteCond %{QUERY_STRING} rewrite
RewriteRule ^(.*)$ http://adc3/new-uri.php$1 [P,E=Proxy-Host:adc3.litespeed.dev]

Result:

This is pretty much the same as rewrite rule , we take same above 3 examples.

Proxy adc.litespeed.dev/index.php to adc2.litespeed.dev/index.php

We will configure the context like screenshot

URI: /index.php

Cluster: adc2

Enable Rewrite: Yes

Rewrite Rules:

RewriteRule ^(.*) - [E=Proxy-Host:adc2.litespeed.dev]

We will need to RewriteRule to alter the hostname, otherwise you will have 404 error.

Please note that Context has a dedicated cluster and does NOT support query string , so you may not be able to proxy to different backend by query string as above rewrite rule example.

This is another example , proxy `adc.litespeed.dev/adc3` to `adc3.litespeed.dev/new-uri.php`

URI: /adc3

Cluster: adc3

Enable Rewrite: Yes

Rewrite Rules:

RewriteRule ^(.*)$ http://adc3/new-uri.php$1 [P,E=Proxy-Host:adc3.litespeed.dev]

Basically all of these are based on RewriteRuleand RewriteCond.

If you are having trouble with rewrite rule , you can also enable rewrite log to help you to analyze to know what result did it eventually rewrite into

In ADC Virtual host ---> RewriteRule tab , set Log Level to 9

You can check the rewrite log in server log , by default it’s /usr/local/lslb/logs/error.log ,

You will see a log like this

[REWRITE] Rule: Match '/index.php' with pattern '^/index.php', result: 1
[REWRITE] set ENV: 'Proxy-Host:adc3.litespeed.dev'
[REWRITE] Source URI: '/index.php' => Result URI: '/new-uri.php'

The first line , end with result: 1 , any positive value means the condition matches , and negative value means the condition does not match.

Another useful tool is regular expression test tool , this will also help you to tweak and check your rewrite rule

and as LiteSpeed ADC is compatible with Apache mod_rewrite syntax , you can also check Apache doc