Apache’s URL rewriting facility can be used to shape URLs piped to Tomcat, but it’s not as simple as it seems.
The basic action is straightforward. First incoming URLs are processed by mod_rewrite, then they are matched up against JkMount definitions to find the appropriate Tomcat connector to use.
The problem is, what Tomcat sees isn’t what you’d expect to have come out from the rewrite process.
What actually happens is that before being submitted to mod_rewrite, the incoming URL is converted to server-relative form. After rewriting, the resulting URL is then reassembled, including the parts that Tomcat doesn’t want or need. Including the Apache DocumentBase path.
To prevent this problem, just qualify the last rewrite rule in the process with the “PT” directive to let Apache know to “Pass Through” the URL without reassembly. So, for example:
RewriteRule ^/$ /mywebapp/index.jsp [L,PT] JkMount /mywebapp/* ajp13