Make "puma-heroku" the default config

[nateberkopec]

The gem is a bit misnamed, it's just "good practices in config". I think we could mainline most of the settings in there for 5.0 and sunset the gem.

[olleolleolle]

The items in puma/puma-heroku to be moved into lib/puma/configuration.rb could include:

• Worker Count via ENV variable where supported: query the environment variable WEB_CONCURRENCY (default: 1) for workers count
  • (unless JRuby or Windows, then do not set it)
• if using workers, preload the app
• Set both min and max threads via ENV variables RAILS_MAX_THREADS, MAX_THREADS:
  • Integer(ENV['RAILS_MAX_THREADS'] || ENV['MAX_THREADS'] || default_value)
  • default_value: 16 on non-MRI platforms
  • default_value: 5 on MRI
• Listen to RAILS_ENV for environment: :environment => -> { ENV['RACK_ENV'] || "development" }, to also include ENV['RAILS_ENV'] - Configuration: Get environment from RAILS_ENV, too #2022
• Unsupported, not to be included Rails 5.2 and lower: pre-fork & on_worker_boot database connecting

---

Q: Any these items that have higher priority? A: Not particularly.

The list has been updated.

[nateberkopec]

@olleolleolle Not particularly. I'm think we can omit the 5.2-and-lower database-connecting stuff, as those versions as no longer officially supported.

RAILS_MIN_THREADS - who uses that?

[olleolleolle]

@nateberkopec From memory: I've only used it because the option setting was there, and then used the same values for "max". Merging them into one useful setting: a good thing.

[nateberkopec]

Also re: Set min and max threads via ENV variable(s): min_threads, max_threads set to Integer(ENV['RAILS_MAX_THREADS'] || ENV['MAX_THREADS'] || 5) (perhaps w/ a RAILS_MIN_THREADS, too?)

We should keep the default of 16 on non-MRI platforms - so we should use a new default of 5 on MRI only.

[jalevin]

#2143 might need a hand with this.. having issues repeating failing tests locally.

[ukolovda]

Hello!
Also it will be useful in Docker containers.
I need read default parameters from environment variables, not from command-line arguments.