Correctly setup Tomcat behind Apache with mod_proxy_ajp - apache

Question

I've been tinkering with Apache + Tomcat so that I can serve multiple tomcat apps (in different machines) through apache (clean & crisp urls rock). I've succesfully configured mod_proxy_ajp & mod_rewrite to the point where I can serve two tomcat apps in different machines with almost no troubles.
The only issue I've found is that one of the apps (which I'm developing in Struts2) has a lot of links and forms, which are generated with <s:a />, <s:url /> and <s:form /> tags. The urls generated by these tags generally are like this:
/WebApp/path/to/some.action
Thanks to the magic of ModRewrite, this is generally not a big issue and hyperlinks poiting to such urls are quickly rewriten & redirected to /app/path/to/some.action (although I do get tons of 302 responses).
The real problem occurs when performing POST requests. As you all might know, I cannot redirect POST requests with mod_rewrite... so in the end... all of my POST requests don't work because mod_rewrite redirects to the correct url but as a GET request.
I have already read a bit about mod_proxy_html and how it can help me rewrite the urls returned by the Tomcat web application... but it feels troublesome.
This is my current apache configuration:
## HACKING BEGINS RIGHT HERE
# cookies
ProxyPassReverseCookiePath /WebApp /app
# this is for CSS, IMGs, JS and redirecting urls with /WebApp*
RewriteRule ^/WebApp(.*)$ /app$1 [R,L]
<Location /app>
ProxyPass ajp://localhost:8009/WebApp
ProxyPassReverse ajp://localhost:8009/WebApp
Order allow,deny
Allow from all
</Location>
# the other app
ProxyPassReverseCookiePath /WebApp2 /other
<Location /other>
ProxyPass ajp://200.9.4.6:8009/WebApp2
ProxyPassReverse ajp://200.9.4.6:8009/WebApp2
Order allow,deny
Allow from all
</Location>
There must be a solution to my POST requests problem... Any ideas? Can I somehow configure something that will allow Struts2 to output correct urls?
Thanks for your help.

Answer 1

There may be a couple ways to go about this.
If you are able to deploy your app to Tomcat under the same name that you are using in the URL, that would be the easiest. So your application app would be /webapps/app[.war] instead of /webapps/WebApp, this would avoid the rewrite altogether.
Otherwise, the following should work, and should go before your current rewrite rule. The [PT] should allow Apache to still proxy the request (this works when using mod_jk, not sure I've used/tested it with mod_proxy_ajp):
RewriteCond %{REQUEST_METHOD} POST
RewriteRule ^/WebApp(.*)$ /app$1 [PT,L]
Once your bean has processed the POST request, you could then send the request to a URL that would be redirected. In the end, the POST URL doesn't matter to the user, so it doesn't have to be a pretty URL.
Edits Below:
I saw on the Apache mod_proxy, that ProxyPassReverse should work with the [PT] flag. And I was able to replicate the issue you're having, and the below config worked for me with a basic JSP page with a form that posted to another JSP page.
<VirtualHost *:80>
ServerName localhost
RewriteEngine On
RewriteCond %{REQUEST_METHOD} !POST
RewriteRule /WebApp/(.*) /app/$1 [R,L]
RewriteCond %{REQUEST_METHOD} POST
RewriteRule /WebApp/(.*) /app/$1 [PT,L]
<Location /app>
ProxyPass ajp://localhost:8109/WebApp
ProxyPassReverse ajp://localhost:8109/WebApp
</Location>
</VirtualHost>

Answer 2

This is a problem with the webapp setup; there may be a way to work around it in httpd config, but it's cleaner to fix the original inconsistency vs. hacking around it.
Also worth mentioning that Struts is trying to help you by giving you context-aware, non-relative URLs; if you just make the paths match, you can rely on that (instead of fighting it...).
So, just deploy the Struts webapp to /app and /other, instead of /WebApp and /WebApp2. (There might be some reason this isn't possible -- like if you don't actually control those other servers -- but it sounds like that doesn't apply).

Answer 3

I would avoid URL rewriting. It just opens cans of worms like this, makes you look into mod_proxy_html, etc, which of course are just yet more worms. Instead just deploy your apps in Tomcat with real URLs you can live with as being visible externally.