Rack Cache Example¶ ↑

This is a example app to demonstrate how to use http-caching with Rack:Cache and Memcached on the Heroku Cedar stack

For more information on http-caching, take a look Ryan Bates screencast #321: railscasts.com/episodes/321-http-caching and this blog post from Ryan Tomayko: tomayko.com/writings/things-caches-do

Example app on Heorku: bit.ly/Ab7fsl

Instructions¶ ↑

1. Add the dalli and rack-cache gem to the Gemfile:

   gem 'dalli'
   gem 'rack-cache'
   

2. Tell cache_store in production.rb to use dalli and config midleware from the Heroku env.:

   In production.rb:
   
   # Use a different cache store in production
   # config.cache_store = :mem_cache_store
   config.cache_store = :dalli_store
   config.middleware.use Rack::Cache,
     :verbose => true,
     :metastore => "memcached://#{ENV['MEMCACHE_SERVERS']}",
     :entitystore => "memcached://#{ENV['MEMCACHE_SERVERS']}"

3. Generate etag and set expires_in your controller action. In this static example I generate the etag based on the last modified date on the index page template:

   def index
     last_modified = File.mtime("#{Rails.root}/app/views/pages/index.html.erb")
     fresh_when last_modified: last_modified , public: true, etag: last_modified
     expires_in 10.seconds, public: true
   end
   

4. Add Memcached to your Heroku app.

5. Verify that Rack:Cache gets loaded by running heroku run rake middleware:

   rack-cache-example (master)$ heroku run rake middleware
   Running rake middleware attached to terminal... up, run.1
   use Rack::Cache
   use ActionDispatch::Static
   use Rack::Lock
   use #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x0000000395e0e0>
   use Rack::Runtime
   use Rack::MethodOverride
   use ActionDispatch::RequestId
   use Rails::Rack::Logger
   use ActionDispatch::ShowExceptions
   use ActionDispatch::DebugExceptions
   use ActionDispatch::RemoteIp
   use ActionDispatch::Callbacks
   use ActiveRecord::ConnectionAdapters::ConnectionManagement
   use ActiveRecord::QueryCache
   use ActionDispatch::Cookies
   use ActionDispatch::Session::CookieStore
   use ActionDispatch::Flash
   use ActionDispatch::ParamsParser
   use ActionDispatch::Head
   use Rack::ConditionalGet
   use Rack::ETag
   use ActionDispatch::BestStandardsSupport
   use Rack::Cache
   run RackCacheExample::Application.routes

6. Verify your setup with heroku logs and curl:

   rack-cache-example (master)$ heroku logs
   2012-03-01T17:31:36+00:00 app[web.1]: cache: [HEAD /] fresh
   2012-03-01T17:31:36+00:00 heroku[router]: HEAD rack-cache-example.herokuapp.com/ dyno=web.1 queue=0 wait=0ms service=9ms status=200 bytes=0
   
   rack-cache-example (master)$ curl -I http://rack-cache-example.herokuapp.com/
   HTTP/1.1 200 OK 
   Age: 2
   Cache-Control: max-age=10, public
   Content-length: 1429
   Content-Type: text/html; charset=utf-8
   Date: Thu, 01 Mar 2012 17:32:55 GMT
   Etag: "eb288d4e68e81d141653d5575d682012"
   Last-Modified: Thu, 01 Mar 2012 17:05:12 GMT

7. When passing in the etag as If-None-Match-header you should see a 304 - not modified response:

   rack-cache-example (master)$ curl -I http://rack-cache-example.herokuapp.com/ --header 'If-None-Match: "eb288d4e68e81d141653d5575d682012"'
   HTTP/1.1 304 Not Modified 
   Age: 4
   Cache-Control: max-age=10, public
   Date: Thu, 01 Mar 2012 17:35:23 GMT
   Etag: "eb288d4e68e81d141653d5575d682012"
   Server: WEBrick/1.3.1 (Ruby/1.9.2/2011-07-09)

8. Voila!