Log puma config if the env variable LOG_CONFIG exists

History.md

@@ -2,6 +2,7 @@
 
 * Features
   * Your feature goes here <Most recent on the top, like GitHub> (#Github Number)
+  * Prints the loaded configuration if the environment variable `LOG_CONFIG` is present ([#2472])
   * Integrate with systemd's watchdog and notification features ([#2438])
   * Adds max_fast_inline as a configuration option for the Server object ([#2406])
   * You can now fork workers from worker 0 using SIGURG w/o fork_worker enabled [#2449]

README.md

@@ -85,6 +85,9 @@ Puma provides numerous options. Consult `puma -h` (or `puma --help`) for a full
 You can also find several configuration examples as part of the
 [test](https://github.com/puma/puma/tree/master/test/config) suite.
 
+For debugging purposes, you can set the environment variable `LOG_CONFIG` with a value
+and the loaded configuration will be printed as part of the boot process.
+
 ### Thread Pool
 
 Puma uses a thread pool. You can set the minimum and maximum number of threads that are available in the pool with the `-t` (or `--threads`) flag:

lib/puma/configuration.rb

@@ -92,6 +92,12 @@ def finalize_values
         end
       end
     end
+
+    def final_options
+      default_options
+        .merge(file_options)
+        .merge(user_options)
+    end
   end
 
   # The main configuration class of Puma.
@@ -290,6 +296,10 @@ def run_hooks(key, arg, events)
       end
     end
 
+    def final_options
+      @options.final_options
+    end
+
     def self.temp_path
       require 'tmpdir'
 

lib/puma/launcher.rb

@@ -87,6 +87,8 @@ def initialize(conf, launcher_args={})
       Puma.stats_object = @runner
 
       @status = :run
+
+      log_config if ENV['LOG_CONFIG']
     end
 
     attr_reader :binder, :events, :config, :options, :restart_dir
@@ -521,5 +523,14 @@ def with_unbundled_env
         Bundler.with_unbundled_env { yield }
       end
     end
+
+    def log_config
+      log "Configuration:"
+
+      @config.final_options
+        .each { |config_key, value| log "- #{config_key}: #{value}" }
+
+      log "\n"
+    end
   end
 end

test/test_config.rb

@@ -265,6 +265,13 @@ def test_config_does_not_load_workers_by_default
     assert_equal 0, Puma::Configuration.new.options.default_options[:workers]
   end
 
+  def test_final_options_returns_merged_options
+    conf = Puma::Configuration.new({ min_threads: 1, max_threads: 2 }, { min_threads: 2 })
+
+    assert_equal 1, conf.final_options[:min_threads]
+    assert_equal 2, conf.final_options[:max_threads]
+  end
+
   private
 
   def assert_run_hooks(hook_name, options = {})

test/test_launcher.rb

@@ -158,6 +158,22 @@ def test_puma_stats_clustered
     launcher.run
   end
 
+  def test_log_config_enabled
+    ENV['LOG_CONFIG'] = "1"
+
+    assert_match(/Configuration:/, launcher.events.stdout.string)
+
+    launcher.config.final_options.each do |config_key, _value|
+      assert_match(/#{config_key}/, launcher.events.stdout.string)
+    end
+
+    ENV.delete('LOG_CONFIG')
+  end
+
+  def test_log_config_disabled
+    refute_match /Configuration:/, launcher.events.stdout.string
+  end
+
   private
 
   def events