Gemfile

gem 'sunspot_rails', :require => 'sunspot/rails'

sunspot.rb

# in config/initializers

Sunspot.session = Sunspot::Rails.build_session
Sunspot::Adapters::InstanceAdapter.register(Sunspot::Rails::Adapters::ActiveRecordInstanceAdapter, ActiveRecord::Base)
Sunspot::Adapters::DataAccessor.register(Sunspot::Rails::Adapters::ActiveRecordDataAccessor, ActiveRecord::Base)
ActiveRecord::Base.module_eval { include(Sunspot::Rails::Searchable) }
ActionController::Base.module_eval { include(Sunspot::Rails::RequestLifecycle) }