herokuでセッションの保存先をRedisにする ref: http://qiita.com/Oakbow/items/98599da0fc62863fc1b8

development.rb

Rails.application.configure do
    :
  # for session store.
  config.session_store_servers = 'redis://localhost:6379/0/session'
    :
end

file5.txt

127.0.0.1:6379> keys session*
1) "session:f1412e2bbe5df2091ebdf2e3025e2335"

Gemfile

gem 'redis'
gem 'redis-rails'

production.rb

Rails.application.configure do
    :
  # for session store.
  config.session_store_servers = ENV["REDISCLOUD_URL"]
    :
end

session_store.rb

# Rails.application.config.session_store :cookie_store, key: 'XXXXXX'
Rails.application.config.session_store :redis_store, servers: Rails.application.config.session_store_servers, expire_in: BestTeacher::Application.config.session_expires_in