In Mac OS X Server 10.2 or later, the web performance cache does not prevent a remote client's IP address from being logged in the access_log. The web performance cache process adds an HTTP header named "PC-Remote-Addr" that contains the client's IP address before passing a request to the Apache web server.
So, with the performance cache disabled, the standard log format string on the CustomLog directive in httpd_macosxserver.conf is as it was in version 10.1:
%h %l %u %t "%r" %>s %b
But when the performance cache is enabled, as it is by default, the "%h" item would extract the local computer's IP address. To extract the remote client's IP address, the log format string needs to be modified:
%{PC-Remote-Addr}i %l %u %t "%r" %>s %b
When you use the Server Settings application (in 10.2) or Server Admin (in 10.3) to enable and disable Web performance cache for each site (virtual host), the CustomLog directive in httpd_macosxserver.conf for each site is automatically adjusted to the correct format string, so this is normally transparent, and your access logs should always contain the correct remote client address.