environment.rb

Rails::Initializer.run do |config|

  # Read from config/memcached.yml to setup Memcache instance
  # Individual caching mechanisms are enabled in environment specific configs
  require 'memcache'
  mservers = if (File.exist?(mconfig = Rails.root+'config'+'memcached.yml'))
    YAML.load_file(mconfig)[RAILS_ENV].delete('servers')
  end
  MemCacheConnection = MemCache.new(mservers || 'localhost:11211', :namespace => "_myapp")
end

memcached.rb

# `load` this file in your deploy.rb
# add the :memcached role to your server with a private_ip attribute:
#   server 'app01.myapp.com', :app, :memcached, :private_ip => '10.1.1.1'
# or just set(:memcached_servers) { ['10.1.1.1', '10.1.1.2'] }

_cset(:memcached_servers) do
  if roles[:memcached].servers.any?
    unless roles[:memcached].servers.all? {|s| s.options[:private_ip] }
      abort "Set :private_ip for all :memcached servers or "+
            "set :memcached_servers explicitly."
    end
    roles[:memcached].servers.map {|s| s.options[:private_ip] + ":11211" }
  else
    %w[localhost:11211]
  end
end

namespace :deploy do
  namespace :memcached do
    desc "Generate the memcached.yml in the shared directory"
    task :config, :roles => :app do
      config = {
        environment => {
          'servers' => fetch(:memcached_servers)
        }
      }
      put YAML.dump(config), "#{shared_path}/config/memcached.yml"
    end
  end
end

production.rb

config.cache_store = :mem_cache_store, MemCacheConnection # Rails.cache