Puma deployment issue with Heroku - ruby-on-rails

Question

I'm trying to deploy my application to Heroku using Puma. This is my first time using Puma, as this is my first attempt at a "production quality" application. I've added puma as described in the dev center but I'm running into a no method error once deployed. Here's my error from the logs: config/puma.rb:5:in _load_from': undefined method preload_app!' for #<Puma::Configuration::DSL:0x007f89e2686140> (NoMethodError)
I used the suggested configuration in my config\puma.rb:
workers Integer(ENV['WEB_CONCURRENCY'] || 2)
threads_count = Integer(ENV['MAX_THREADS'] || 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
end
as shown in the error above, it seems Heroku has a problem with the preload_app! command. I'm stuck and don't know where to go from here - I have a feeling I somehow miscreated the file - i.e. I just made a new file in my editor rather than from the command line.

Answer 1

This is how we set config/puma.rb up on Heroku using Rails 4.1.0
workers Integer(ENV['PUMA_WORKERS'] || 3)
threads Integer(ENV['MIN_THREADS'] || 1), Integer(ENV['MAX_THREADS'] || 16)
preload_app!
rackup DefaultRackup
port ENV['PORT'] || 3000
environment ENV['RACK_ENV'] || 'development'
on_worker_boot do
# worker specific setup
ActiveSupport.on_load(:active_record) do
config = ActiveRecord::Base.configurations[Rails.env] ||
Rails.application.config.database_configuration[Rails.env]
config['pool'] = ENV['MAX_THREADS'] || 16
ActiveRecord::Base.establish_connection(config)
end
end
We keep the workers and threads to a minimum (we are on the free plan).
When I restart our dyno, I get this output in the logs:
2015-03-.. app[web.1]: [3] Puma starting in cluster mode...
2015-03-... app[web.1]: [3] * Version 2.9.1 (ruby 2.1.5-p273), codename: Team High Five
2015-03-... app[web.1]: [3] * Min threads: 1, max threads: 3
2015-03-... app[web.1]: [3] * Environment: production
2015-03-... app[web.1]: [3] * Process workers: 2
2015-03-... app[web.1]: [3] * Preloading application