As with most upgrades / deploy on production, if things go awry, we may have to rollback.

Due to some unexpected behavior, we decided to rollback Rails 4 Upgrade and Boom !! started getting lot of exceptions

NoMethodError: undefined method 'sweep' for Hash

as session cookies blowed up due to different Data Structures in Rails 4 & 3 and not backward-compatible :(

• Created config/initializers/rails4_to_rails3_downgradability.rb
  • Refer gist

Enjoy Rails 4 !!!