Setting up Puma and Rails on Heroku

puma_rails_heroku.rb

# Gemfile
gem "puma"

# Procfile
web: bundle exec puma -p $PORT -e $RACK_ENV -C config/puma.rb

# add to config block config/environments/production.rb
config.threadsafe!

# get rid of NewRelic after_fork code, if you were doing this:
# http://support.newrelic.com/kb/troubleshooting/unicorn-no-data
# and get rid of config/unicorn.rb if you were using that

# config/puma.rb
require "active_record"
cwd = File.dirname(__FILE__)+"/.."
ActiveRecord::Base.connection.disconnect! rescue ActiveRecord::ConnectionNotEstablished
ActiveRecord::Base.establish_connection(ENV["DATABASE_URL"] || YAML.load_file("#{cwd}/config/database.yml")[ENV["RACK_ENV"]])
ActiveRecord::Base.verify_active_connections!

# if you use NewRelic, set your NEWRELIC_DISPATCHER environment variable on heroku, per
# https://github.com/puma/puma/issues/128 - may not be needed for future releases of Puma

heroku config:add NEWRELIC_DISPATCHER=Puma

heroku config:add NEWRELIC_DISPATCHER=Puma will make New Relic think ALL Heroku processes are Pumas, including workers and one-off heroku run rails c.

I know Puma 2 makes this setting unnecessary, but it's still in beta so I'm on the latest 1x (1.6.3).

Does anybody know how to detect what Heroku PS type was invoked? Or some other way to tell if I'm running on a web dyno or not? I figure I can use that knowledge in an initializer to only set ENV[NEWRELIC_DISPATCHER]=Puma for web dynos.

An alternative approach that helps increase AR's connection pool size on Heroku has been published in the Heroku dev center.

config.threadsafe! is deprecated for rails 4:

"Rails applications behave by default as thread safe in production as long as config.cache_classes and config.eager_load are set to true."

ActiveRecord::Base.verify_active_connections! is also deprecated, and should be removed.

yeah you don't need a puma.rb file. That was vestigial from when I was on unicorn, and I thought had read somewhere that puma needed it to be able to restart cleanly

here's the relevant info for the new cool way to do it https://devcenter.heroku.com/articles/concurrency-and-database-connections#connection-pool