Update for Rails 7.2: config/puma.rb (with Heroku-specific setttings)

Author: yasulab

config/puma.rb

@@ -1,42 +1,42 @@
-# 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.
+#
+# The default is set to 3 threads as it's deemed a decent compromise between
+# throughput and latency for the average Rails application.
 #
-environment ENV.fetch("RAILS_ENV") { "development" }
+# 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
+
+# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
+port ENV.fetch("PORT", 3000)
 
-# Specifies the `pidfile` that Puma will use.
-pidfile ENV.fetch("PIDFILE") { "tmp/pids/server.pid" }
+# Allow puma to be restarted by `bin/rails restart` command.
+plugin :tmp_restart
 
-# 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).
-#
-workers ENV.fetch("WEB_CONCURRENCY") { 2 }
+# Specify the PID file. Defaults to tmp/pids/server.pid in development.
+# In other environments, only set the PID file if requested.
+pidfile ENV["PIDFILE"] if ENV["PIDFILE"]
 
 # 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!
 
 before_fork do
@@ -47,6 +47,3 @@
 
   PumaWorkerKiller.enable_rolling_restart # Default is every 6 hours
 end
-
-# Allow puma to be restarted by `rails restart` command.
-plugin :tmp_restart