November 5, 2011
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We recently had a scenario where an apache reverse proxy needed to be deployed in front of a pair of tomcat servers. Due to security concerns, this reverse proxy was hosting mod_security and acting as a web application firewall (WAF)
However, a critical requirement was that the tomcat applications would be able to see the original IP address of the client. This presented a problem because unlike squid, apache has no configurable option to act as a fully transparent proxy. In other words, once traffic was redirected through the apache reverse proxy, the traffic forwarded to the tomcat server was forwarded with it’s source IP address changed to the proxy, effectively hiding the public IP the client used to connect to the site.
The first solution that sprang to mind was the “X-Forwarded-For” headers, which is an HTTP header inserted into the original HTTP GET request whose value is equal to the client’s public IP. Turns out apache reverse proxy inserts this header by default, and even so the tomcat application could not extract the client’s IP. We somehow needed to instruct the tomcat server itself to provide the application with the correct client IP.
The solution that worked in my case was the RemoteIP tomcat valve. Official documentation lives here:
It’s quite simple to configure in that all that needs to be done is to modify tomcat server.xml to recognise original client IP rather than the proxy IP by adding the following to server.xml:
make sure to change 127.0.0.1 to the address of the apache reverse proxy.
The application could now recognise the original client IP.
PS as per the tomcat documentation, the apache equivalent of the above method is using the mod_remoteip