When ProxyPass and ProxyPassReverse aren’t enough

July 1, 2013 | By Brian | Filed in: work.

If you’ve ever used ProxyPass and ProxyPassReverse you know how awesomely powerful they are when integrating multiple backends and keeping the things neat and tidy in Apache.

Recently I had to integrate with a backend app using Apache as a reverse proxy. Ideally, and how I’ve done it a million times in the past, you are able to have the backend application respond on a particular host/port/path ( i.e. http://foo.example.com:1234/backend ). This makes setting up Apache via ProxyPass and ProxyPassReverse a snap.

  ProxyPass        /backend/ http://foo.example.com:1234/backend/
 ProxyPassReverse /backend/ http://foo.example.com:1234/backend/

So what happens when you can’t run the backend application on a specific context root? By that I mean it can only run at: http://foo.example.com:1234/.

This is where mod_proxy_html comes in. In a nutshell, mod_proxy_html allows you to rewrite html, javascript & css so that the URLs can cleanly go through your reverse proxy. This means that the backend application responds with

<script src="/script/application.js" type="text/javascript"></script>

mod_proxy_html will converted it to

<script src="/backend/script/application.js" type="text/javascript"></script>

To get this to work, add the following to httpd.conf

Include conf.d/proxy_html.conf

ProxyPass        /backend/ http://foo.example.com:1234/
ProxyPassReverse /backend/ http://foo.example.com:1234/
ProxyHTMLURLMap http://foo.example.com:1234 /backend

<Location /backend/>
  ProxyHTMLEnable On
  ProxyPassReverse http://foo.example.com:1234/
  SetOutputFilter proxy-html
  ProxyHTMLURLMap / /backend/
  ProxyHTMLURLMap /backend /backend

mod_proxy_html is available in Apache 2.4, and as a 3rd party installable module in older Apache 2.x. I needed it in Apache 2.2 on Centos 6 and used the RPM from epel.

This post just scratches the surface with what you can do with mod_proxy_html. There are a ton of options for configuring meta headers, html fixups, and buffer sizes. Go check it out!

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