I'm building a rails app that I'll host on Heroku at domain.com. And I'd like to use WordPress for the blog hosted on phpfog, but I don't want to use a subdomain like blog.domain.com. I'd instead prefer to use a subdirectory like domain.com/blog
Its not about SEO...I'm just not a fan of subdomains. Subdirectories are sexier (yeah...I actually said that).
Any idea on how I can reliably accomplish this? Thanks in advance for the help.
You can use the rack-reverse-proxy gem that neezer found to do this.  First you'll want to add gem "rack-reverse-proxy", :require => "rack/reverse_proxy" to your Gemfile and run bundle install.  Next, you'll modify your config.ru to forward the /blog/ route to your desired blog:
require ::File.expand_path('../config/environment',  __FILE__)  use Rack::ReverseProxy do          reverse_proxy /^\/blog(\/.*)$/, 'http://notch.tumblr.com$1', opts={:preserve_host => true} end  run YourAppName::Application   You probably already have the first require statement and the run YourAppName... statement.  There are a couple important details that make this work.  
First, when you add your desired blog URL, you can't keep the trailing slash on it.  If you do, when someone requests http://yourdomain.com/blog/, the gem will forward them to http://you.yourbloghost.com// with an extra trailing slash.  
Secondly, if the :preserve_host option isn't enabled, your blog hosting server will see the request as being for http://yourdomain.com/blog/ instead of as http://you.yourbloghost.com and will return bad results.  
You still may have an issue with the CSS or images if the blog uses /absolute/paths/to/images/.
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