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502 Proxy Error – Apache reverse proxy

Posted on 08 June 2010

I configured an Apache2 reverse proxy as described here.  I could get the index page of the site to load but the css wasn’t getting applied.  If I clicked any links on the site I get a 502 proxy error.

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /page2.html.

Reason: DNS lookup failure for: internal.domain3.compage2.html

I noticed that URL in the Reason line was missing the / between the domain and page2.html, but since it was present in the GET /page2.html I dismissed that clue.  I launched into troubleshooting mode and checked DNS resolution, mod_proxy config, caching, etc.

Finally I took a shot in the dark and went back to the original error.  I added a terminal / (shown in red below) to the mod_proxy statements in my httpd.conf file and if flipping worked.  I didn’t see this required in any of the documents I read on configuring mod_proxy but who know’s.  Maybe I’m a dumbass.

 ProxyPass / http://internal.domain3.com/
 ProxyPassReverse / http://internal.domain3.com/
 ProxyHTMLURLMap http://internal.domain3.com/ /