Use JSON-format structured logging in production

Author: mwtrew

Gemfile

@@ -43,6 +43,7 @@ gem 'puma', '~> 8.0'
 gem 'rack_content_type_default', '~> 1.1'
 gem 'rack-cors'
 gem 'rails', '~> 8.1.3'
+gem "rails_semantic_logger", "~> 4.20"
 gem 'ruby-progressbar', '~> 1.13', require: false
 gem 'ruby-vips'
 gem 'sentry-rails'

Gemfile.lock

@@ -403,6 +403,10 @@ GEM
     rails-html-sanitizer (1.7.0)
       loofah (~> 2.25)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
+    rails_semantic_logger (4.20.0)
+      rack
+      railties (>= 5.1)
+      semantic_logger (~> 4.16)
     railties (8.1.3)
       actionpack (= 8.1.3)
       activesupport (= 8.1.3)
@@ -513,6 +517,8 @@ GEM
       childprocess (>= 0.5, < 5.0)
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2)
+    semantic_logger (4.18.0)
+      concurrent-ruby (~> 1.0)
     sentry-rails (6.6.0)
       railties (>= 5.2.0)
       sentry-ruby (~> 6.6.0)
@@ -618,6 +624,7 @@ DEPENDENCIES
   rack_content_type_default (~> 1.1)
   rails (~> 8.1.3)
   rails-erd
+  rails_semantic_logger (~> 4.20)
   rspec
   rspec-rails
   rspec_junit_formatter

config/environments/production.rb

@@ -45,10 +45,12 @@
   # Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
   # config.force_ssl = true
 
-  # Log to STDOUT by default
-  config.logger = ActiveSupport::Logger.new($stdout)
-                                       .tap  { |logger| logger.formatter = Logger::Formatter.new }
-                                       .then { |logger| ActiveSupport::TaggedLogging.new(logger) }
+  # Log to STDOUT on Heroku in JSON format, where this variable is set automatically.
+  if ENV["RAILS_LOG_TO_STDOUT"].present?
+    $stdout.sync = true
+    config.rails_semantic_logger.add_file_appender = false
+    config.semantic_logger.add_appender(io: $stdout, formatter: :json)
+  end
 
   # Prepend all log lines with the following tags.
   config.log_tags = [:request_id]