Puma with auto worker count

puma.rb

pidfile ENV.fetch('PUMA_PID_PATH','/tmp/pid')
# Should not be a solution
worker_timeout Integer(ENV.fetch('PUMA_WORKER_TIMEOUT', 60))
# Default worker ( OS processes ) is set to 4 ( most machines has 4 cores )
# But adjust depending on context ( how much CPU are given to my container ? )
current_cpu_count = begin
                      Integer(`nproc`) - 1
                    rescue
                      4
                    end
workers Integer(ENV.fetch('PUMA_WORKER_COUNT', current_cpu_count))
# I doubt the application is thread safe.
# If it is thread safe then you can increase this number.
threads_count = Integer(ENV.fetch('PUMA_MAX_THREADS', 1))
threads threads_count, threads_count
preload_app!
rackup      DefaultRackup
port        ENV.fetch('PUMA_PORT', 3000)
environment ENV.fetch('RAILS_ENV', 'development')
on_worker_boot do
  # after Rails 4.1 just whole block replace by ActiveRecord::Base.establish_connection
  # and set pool in database.yml
  ActiveSupport.on_load(:active_record) do
    config = ActiveRecord::Base.configurations[Rails.env] ||
             Rails.application.config.database_configuration[Rails.env]
    config['pool'] = threads_count
    ActiveRecord::Base.establish_connection(config)
  end
end