You can place a *.erb file in this directory and the set_roles script will 
format them.  This is helpful if you want to customize your balancer_members
or nginx_upstream_members files.  For example, if you want to define multiple
instances for nginx to hook into, you can put something like this in
nginx_upstream_members.erb:

upstream mongrel{
<% 
roles[:app].each do |address| 
  @web_port_range.each do |port|
%>
  server <%= address %>:<%= port %>;
<%
  end
end
%>
  fair;
}

upstream merb{
<% 
@roles[:app].each do |address| 
%>
  server <%= address %>:4000;
  server <%= address %>:4001;
  server <%= address %>:4002;
  server <%= address %>:4003;
  server <%= address %>:4004;
  server <%= address %>:4005;
<% end %>
  fair;
}
