puma.rb

threads_count = ENV.fetch('RAILS_MAX_THREADS') { 5 }.to_i
threads threads_count, threads_count
port ENV.fetch('PORT') { 3000 }

env = ENV.fetch('RAILS_ENV') { 'development' }
environment env

plugin :tmp_restart

unless env == 'test' || env == 'development'
  workers ENV.fetch('WEB_CONCURRENCY') { 1 }
  set_remote_address header: 'X-Real-IP'
  queue_requests false
  preload_app!
end

RAILS_MAX_THREADS=1

queue_requests false is a recent addition as we are waiting on puma/puma#1737