Default Sidekiq Redis configuration in Rails app

I'm trying to understand the Redis & Sidekiq configuration in a Passenger+Rails app and have run into some lack of understanding. I start the redis server independently of my rails app, while Sidekiq is a gem in my Rails app. I start it likewise: (no sidekiq.yml file needed for me)

bundle exec sidekiq

Following is my sidekiq.rb initializer:

require 'sidekiq'require 'sidekiq-status'Sidekiq.configure_client do |config|  config.client_middleware do |chain|    chain.add Sidekiq::Status::ClientMiddleware  endendSidekiq.configure_server do |config|  config.server_middleware do |chain|    chain.add Sidekiq::Status::ServerMiddleware, expiration: 30.minutes  end  config.client_middleware do |chain|    chain.add Sidekiq::Status::ClientMiddleware  endend

I went through some library classes, but to no avail.

I want to understand where does Sidekiq configure it's Redis server details. It defaults to localhost:6379, but I am not quite sure how.
Also, if I wish to use Memcached in future, how can I change that?