title: What is the point of Varnish and Rack-Cache for a Rails app?
body: <p>I am a bit confused about the purpose of Varnish and Rack-Cache for a Rails app. In <code>config/environments/production.rb</code> caching can be set with something like</p>
  
  <p><code>config.static_cache_control = "public, max-age=3600"</code></p>
  
  <p>Given that, what exactly is the purpose of Varnish and Rack-Cache if you can set caching in the Rails app itself?</p>
  
  <p>And what causes the default Rails app to use rack-cache?</p>