Use Puma as development & testing server (#9683)

* Use Puma in dev and test environments

* Update Puma default configuration per Rails 7.2

Gemfile

@@ -117,6 +117,8 @@ group :development, :test do
   gem 'faker'
   gem 'capybara-screenshot'
 
+  gem 'puma'
+
   gem 'byebug'
   gem 'i18n-tasks'
   gem 'i18n-spec'

Gemfile.lock

@@ -539,6 +539,8 @@ GEM
     psych (5.1.2)
       stringio
     public_suffix (6.0.0)
+    puma (6.4.2)
+      nio4r (~> 2.0)
     raabro (1.4.0)
     racc (1.8.0)
     rack (2.2.9)
@@ -899,6 +901,7 @@ DEPENDENCIES
   openssl
   overcommit
   premailer-rails
+  puma
   rack (~> 2)
   rack-cors
   rails

config/puma.rb

@@ -1,45 +1,56 @@
 # frozen_string_literal: true
 
-# Puma can serve each request in a thread from an internal thread pool.
-# The `threads` method setting takes two numbers: a minimum and maximum.
-# Any libraries that use thread pools should be configured to match
-# the maximum value specified for Puma. Default is set to 5 threads for minimum
-# and maximum; this matches the default thread size of Active Record.
-#
-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
+# This configuration file will be evaluated by Puma. The top-level methods that
+# are invoked here are part of Puma's configuration DSL. For more information
+# about methods provided by the DSL, see https://puma.io/puma/Puma/DSL.html.
 
-# Specifies the `worker_timeout` threshold that Puma will use to wait before
-# terminating a worker in development environments.
+# Puma starts a configurable number of processes (workers) and each process
+# serves each request in a thread from an internal thread pool.
 #
-worker_timeout 3600 if ENV.fetch("RAILS_ENV", "development") == "development"
-
-# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
+# The ideal number of threads per worker depends both on how much time the
+# application spends waiting for IO operations and on how much you wish to
+# to prioritize throughput over latency.
 #
-port ENV.fetch("PORT", 3000)
-
-# Specifies the `environment` that Puma will run in.
+# As a rule of thumb, increasing the number of threads will increase how much
+# traffic a given process can handle (throughput), but due to CRuby's
+# Global VM Lock (GVL) it has diminishing returns and will degrade the
+# response time (latency) of the application.
 #
-environment ENV.fetch("RAILS_ENV", "development")
-
-# Specifies the `pidfile` that Puma will use.
-pidfile ENV.fetch("PIDFILE", "tmp/pids/server.pid")
-
-# Specifies the number of `workers` to boot in clustered mode.
-# Workers are forked web server processes. If using threads and workers together
-# the concurrency of the application would be max `threads` * `workers`.
-# Workers do not work on JRuby or Windows (both of which do not support
-# processes).
+# The default is set to 3 threads as it's deemed a decent compromise between
+# throughput and latency for the average Rails application.
 #
-# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
+# Any libraries that use a connection pool or another resource pool should
+# be configured to provide at least as many connections as the number of
+# threads. This includes Active Record's `pool` parameter in `database.yml`.
+threads_count = ENV.fetch("RAILS_MAX_THREADS", 3)
+threads threads_count, threads_count
 
-# Use the `preload_app!` method when specifying a `workers` number.
-# This directive tells Puma to first boot the application and load code
-# before forking the application. This takes advantage of Copy On Write
-# process behavior so workers use less memory.
-#
-# preload_app!
+# Specifies the `environment` that Puma will run in.
+rails_env = ENV.fetch("RAILS_ENV", "development")
+environment rails_env
+
+case rails_env
+when "production"
+  # If you are running more than 1 thread per process, the workers count
+  # should be equal to the number of processors (CPU cores) in production.
+  #
+  # Automatically detect the number of available processors in production.
+  require "concurrent-ruby"
+  workers_count = Integer(ENV.fetch("WEB_CONCURRENCY") { Concurrent.available_processor_count })
+  workers workers_count if workers_count > 1
+
+  preload_app!
+when "development"
+  # Specifies a very generous `worker_timeout` so that the worker
+  # isn't killed by Puma when suspended by a debugger.
+  worker_timeout 3600
+end
 
-# Allow puma to be restarted by `rails restart` command.
+# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
+port ENV.fetch("PORT", 3000)
+
+# Allow puma to be restarted by `bin/rails restart` command.
 plugin :tmp_restart
+
+# Only use a pidfile when requested
+pidfile ENV["PIDFILE"] if ENV["PIDFILE"]

spec/rails_helper.rb

@@ -42,7 +42,6 @@
 end
 
 Capybara.javascript_driver = :apparition
-Capybara.server = :webrick
 
 RSpec.configure do |config|
   # enforce consistent locale behaviour across OSes, especially Linux