Puma: Unable to load application: NameError: uninitialized constant

Question

When I am trying to deploy an rails application to Heroku, I am getting this error:

Puma starting in single mode...
2017-02-27T15:08:03.908788+00:00 app[web.1]: * Version 3.7.0 (ruby 2.3.1-p112), codename: Snowy Sagebrush
2017-02-27T15:08:03.908789+00:00 app[web.1]: * Min threads: 5, max threads: 5
2017-02-27T15:08:03.908790+00:00 app[web.1]: * Environment: production
2017-02-27T15:08:05.942041+00:00 app[web.1]: ! Unable to load application: NameError: uninitialized constant Api::V1::AController
2017-02-27T15:08:05.942133+00:00 app[web.1]: bundler: failed to load command: puma (/app/vendor/bundle/ruby/2.3.0/bin/puma)
2017-02-27T15:08:05.942266+00:00 app[web.1]: NameError: uninitialized constant Api::V1::AController

Here is the link to the full log

If I try to run the following code on my dev environment, everything works just fine:

bundle exec puma -C config/puma.rb

I ran rails on my local machine using the -e production flag and it runs ok, no error appears. This happens only when I deploy to Heroku.

puma.rb

workers Integer(ENV['WEB_CONCURRENCY'] || 2)
threads_count = Integer(ENV['RAILS_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
    ActiveRecord::Base.establish_connection
end

What I've tried:

1. Created a new instance on Heroku just to be sure there was not a problem with the current instance
2. Tested multiple versions of Puma
3. Checked development.rb and production.rb to see what was different

What I am doing right now:

1. Going through each commit to find what changed in the app and try to find the cause of the app

I believe I am overcomplicating the problem... Any thoughts on this?

Answer 1

Try to reproduce this problem on your local machine by setting all environmental variables to the same values as on Heroku. Or at least set all variables used by puma:

RAILS_ENV=production RACK_ENV=production WEB_CONCURRENCY=1 RAILS_MAX_THREADS=5 bundle exec puma -C config/puma.rb

Also I've noticed that you are using threads. Is it on purpose? I mean ruby ecosystem is not famous for thread safety. Try changing RAILS_MAX_THREADS to 1 and bump WEB_CONCURRENCY to higher number.

Answer 2

For me, the application was not using ActiveRecord, but there were still references to it. Because require "active_record/railtie" was commented out, it broke on production.