Variables and proxy_pass

[Jonathan Dance]

Hello,

I'm now trying to use variables to allow me to re-use configuration
files easily. The basic idea is:

upstream some-mongrel-cluster {
   ...
}

server {
 ...
 set $rails_proxy http://some-mongrel-cluster;
 include macros/rails.conf;
}


Then, rails.conf has the standard rails stuff and this line:
proxy_pass $rails_proxy;

Not surprisingly, this doesn't work. :) I am wondering what I might do
to make it work, but I need to know:
- Whether the problem is that the variable is not available from
mod_http_proxy (since "set" is a mod_rewrite command?) or just that
proxy_pass does not support using variables
- If proxy_pass does not support variables, how do I make it do this?
Where in the source is a good place to see how variables work?

Thanks!

JD