What configuration for Rails 3.2.22.2 + Puma + Heroku? - ruby-on-rails-3

Question

I've read Richard Schneeman's article, and a bunch of other ones. ;-)
I'm still struggling with this.
Here's few gems I've added in my Gemfile to benchmark my app:
gem 'airbrake'
gem 'newrelic_rpm'
gem 'stackprof'
gem 'derailed', group: :development
gem 'rack-mini-profiler'
gem 'flamegraph'
gem 'memory_profiler'
gem "skylight"
After a lots of benchmarks in development and in staging env, I know where my app is not fast enough but there's not memory leak (some small mem bloats sometimes maybe).
newapp-staging app is the new version (aka: new frontend, upgraded gems, optimized queries, ...) of oldapp-production app.
Please have a look at the screenshots (oldapp-production use webrick, newapp-staging use puma)
So here comes 2 simple questions:
question #1
newapp-staging app is using ruby '2.2.0' & rails '3.2.22.2' and I can't ensure that it is threadsafe because of my code and the associated gems, so... I must use 1 thread at a time. Is puma an advantage here? Metrics are telling me not.
OR... my configuration is not good. (missing preload_app! maybe, or other things?) Here's my Procfile:
web: bundle exec puma -t 1:1 -p ${PORT:-3000} -e ${RACK_ENV:-development}
worker: bundle exec rake jobs:work
question #2
Unicorn could be used as a replacement?
Thank you for your time and your advices.
Cheers

Answer 1

Using unicorn is the best move here. Here's my configuration if that could help anyone.
Gemfile:
gem 'unicorn'
gem 'unicorn-rails'
group :production, :staging do
gem 'unicorn-worker-killer'
end
Procfile:
web: bundle exec unicorn -p $PORT -c ./config/unicorn.rb
worker: bundle exec rake jobs:work
config/unicorn.rb
worker_processes Integer(ENV["WEB_CONCURRENCY"] || 2)
timeout 15
preload_app true
before_fork do |server, worker|
Signal.trap 'TERM' do
puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
Process.kill 'QUIT', Process.pid
end
defined?(ActiveRecord::Base) and
ActiveRecord::Base.connection.disconnect!
end
after_fork do |server, worker|
Signal.trap 'TERM' do
puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to send QUIT'
end
defined?(ActiveRecord::Base) and
ActiveRecord::Base.establish_connection
end
config.ru
if ENV['RAILS_ENV'] == 'production' || ENV['RAILS_ENV'] == 'staging'
require 'unicorn/worker_killer'
use Unicorn::WorkerKiller::MaxRequests, 768, 1024, true
use Unicorn::WorkerKiller::Oom, (450*(1024**2)), (490*(1024**2)), 16, true
end
require ::File.expand_path('../config/environment', __FILE__)
use Rack::Deflater
run MyApp::Application
On Heroku:
2 x `Standard 2X dynos` for web
1 x `Standard 1X dyno` for worker
Heroku config vars:
SENSIBLE_DEFAULTS: enabled (just in case) & WEB_CONCURRENCY: 2
Cheers