puma_config.rb

workers Integer(ENV['WEB_CONCURRENCY'] || 2) # currently not set, so 2
threads_count = Integer(ENV['MAX_THREADS'] || 5) # currently not set, so 5
threads threads_count, threads_count

preload_app!

rackup      DefaultRackup
port        ENV['PORT']     || 3000
environment ENV['RACK_ENV'] || 'development'

on_worker_boot do
  # Worker specific setup for Rails 4.1+, See:
  # https://devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server#on-worker-boot
  ActiveRecord::Base.establish_connection
  if defined?(Resque)
    Resque.redis = ENV["<redis-uri>"] || "redis://127.0.0.1:6379"
  end
end