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:

https://github.com/yabeda-rb/yabeda/issues/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.