Got empty response from metrics endpoint when starting server via bundle exec puma.

[hanyueitaro]

Overview

Hello.

I use this gem integrating with rails. However,

• When I run rails app via bundle exec puma -C config/puma.rb, I get empty response from metrics endpoint.
• On the other hand, when via bundle exec rails s, I get valid response from metrics endpoint.

This may be caused by the similar problem:

yabeda-rb/yabeda#15

Reproduce

I reproduced this problem in puma single worker mode, and exposing metrics on different port from puma.

• ruby: 3.0.2
• rails: 6.1.4.1
• gems:
  • yabeda-puma-plugin: 0.6.0
  • yabeda-prometheus: 0.7.0
  • yabeda: 0.11.0
  • prometheus-client: 2.1.0
• config/puma.rb:

max_threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }
min_threads_count = ENV.fetch("RAILS_MIN_THREADS") { max_threads_count }
threads min_threads_count, max_threads_count
worker_timeout 3600 if ENV.fetch("RAILS_ENV", "development") == "development"

port ENV.fetch("PORT") { 3000 }

environment ENV.fetch("RAILS_ENV") { "development" }

pidfile ENV.fetch("PIDFILE") { "tmp/pids/server.pid" }

# workers ENV.fetch("WEB_CONCURRENCY") { 2 }

plugin :tmp_restart
activate_control_app
plugin :yabeda
plugin :yabeda_prometheus

[jsimpson]

I also ran into this problem yesterday when setting up Yabeda w/the Puma and Prometheus plugins.

[zabolotnov87]

The issue occurs when you try to start the puma server directly: bundle exec puma -C config/puma.rb

What happens:

1. puma reads config file, finds plugin :yabeda and requires lib/puma/plugin/yabeda.rb
2. then executes require 'yabeda/puma/plugin.rb'
3. then require 'yabeda'
4. then require "yabeda/railtie" if defined?(Rails) https://github.com/yabeda-rb/yabeda/blob/00ebff7036d9adcee9790e7612c3894b26a712cf/lib/yabeda.rb#L11

defined?(Rails) returns nil, so railtie is not loaded and Yabeda.configure! will not be invoked: https://github.com/yabeda-rb/yabeda/blob/7b578d8cb9ff72a2c33f954344e37f9fdeff72d0/lib/yabeda/railtie.rb#L7

As a workaround, you can add require "yabeda/railtie" into your config/initializers/yabeda.rb.

[Envek]

Thanks a lot for your investigation, @zabolotnov87!

I didn't even think about railtie, but now it seems to be pretty obvious 🤦

[chornbec]

Are there updated instructions for this plugin when running puma directly with bundle exec puma ...? I've followed these instructions and I still get a undefined method registry' for module Yabeda::Prometheus::Mmap` error. After reading the mentioned issue here, the plugin only works if I have the following:

# ./config/initializers/yabeda.rb
# I actually found that I don't even need this file for the plugin to work...
require 'yabeda/railtie'

# ./config/puma.rb
# ...
# ...
require 'yabeda/prometheus/mmap'
activate_control_app
plugin :yabeda
plugin :yabeda_prometheus

before_fork do # for puma cluster mode
  Yabeda.configure!
end

# Gemfile
# ... some other gems
gem 'yabeda'
gem 'yabeda-prometheus-mmap'
gem 'yabeda-puma-plugin'
# ... some other gems

Is this setup expected? Doesn't look as straightforward as the docs make it seem.