Silence healthcheck requests from the log (rails#52789)

* Add SilenceRequest middleware

* Make config.silence_healthcheck a way to quiet "/up"

Author: dhh

guides/source/configuring.md

@@ -593,6 +593,14 @@ config.session_store :my_custom_store
 
 The default store is a cookie store with the application name as the session key.
 
+#### `config.silence_healthcheck_path`
+
+Specifies the path of the healthcheck that should be silenced in the logs. Uses `Rails::Rack::SilenceRequest` to implement the silencing. All in service of keeping healthchecks from clogging the production logs, especially for early-stage applications.
+
+```
+config.silence_healthcheck_path = "/up"
+```
+
 #### `config.ssl_options`
 
 Configuration options for the [`ActionDispatch::SSL`](https://api.rubyonrails.org/classes/ActionDispatch/SSL.html) middleware.

railties/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Add Rails::Rack::SilenceRequest middleware and use it via `config.silence_healthcheck_path = path`
+    to silence requests to "/up". This prevents the Kamal-required healthchecks from clogging up
+    the production logs.
+
+    *DHH*
+
 *   Introduce `mariadb-mysql` and `mariadb-trilogy` database options for `rails new`
 
     When used with the `--devcontainer` flag, these options will use `mariadb` as the database for the

railties/lib/rails.rb

@@ -12,6 +12,7 @@
 require "rails/deprecator"
 require "rails/application"
 require "rails/backtrace_cleaner"
+require "rails/rack/silence_request"
 
 require "active_support/railtie"
 require "action_dispatch/railtie"

railties/lib/rails/application/configuration.rb

@@ -15,7 +15,7 @@ class Configuration < ::Rails::Engine::Configuration
                     :cache_classes, :cache_store, :consider_all_requests_local, :console,
                     :eager_load, :exceptions_app, :file_watcher, :filter_parameters, :precompile_filter_parameters,
                     :force_ssl, :helpers_paths, :hosts, :host_authorization, :logger, :log_formatter,
-                    :log_tags, :railties_order, :relative_url_root,
+                    :log_tags, :silence_healthcheck_path, :railties_order, :relative_url_root,
                     :ssl_options, :public_file_server,
                     :session_options, :time_zone, :reload_classes_only_on_change,
                     :beginning_of_week, :filter_redirect, :x,
@@ -62,6 +62,7 @@ def initialize(*)
         @exceptions_app                          = nil
         @autoflush_log                           = true
         @log_formatter                           = ActiveSupport::Logger::SimpleFormatter.new
+        @silence_healthcheck_path                = nil
         @eager_load                              = nil
         @secret_key_base                         = nil
         @api_only                                = false

railties/lib/rails/application/default_middleware_stack.rb

@@ -54,6 +54,10 @@ def build_stack
           middleware.use ::ActionDispatch::RequestId, header: config.action_dispatch.request_id_header
           middleware.use ::ActionDispatch::RemoteIp, config.action_dispatch.ip_spoofing_check, config.action_dispatch.trusted_proxies
 
+          if path = config.silence_healthcheck_path
+            middleware.use ::Rails::Rack::SilenceRequest, path: path
+          end
+
           middleware.use ::Rails::Rack::Logger, config.log_tags
           middleware.use ::ActionDispatch::ShowExceptions, show_exceptions_app
           middleware.use ::ActionDispatch::DebugExceptions, app, config.debug_exception_response_format

railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt

@@ -60,6 +60,9 @@ Rails.application.configure do
   # Skip http-to-https redirect for the default health check endpoint.
   # config.ssl_options = { redirect: { exclude: ->(request) { request.path == "/up" } } }
 
+  # Prevent healthchecks from clogging up the logs
+  config.silence_healthcheck_path = "/up"
+
   # Log to STDOUT by default
   config.logger = ActiveSupport::Logger.new(STDOUT)
     .tap  { |logger| logger.formatter = ::Logger::Formatter.new }

railties/lib/rails/rack/silence_request.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+# :markup: markdown
+
+require "active_support/logger_silence"
+
+module Rails
+  module Rack
+    # Allows you to silence requests made to a specific path.
+    # This is useful for preventing recurring requests like healthchecks from clogging the logging.
+    # This middleware is used to do just that against the path /up in production by default.
+    #
+    # Example:
+    #
+    #   config.middleware.insert_before \
+    #     Rails::Rack::Logger, Rails::Rack::SilenceRequest, path: "/up"
+    #
+    # This middleware can also be configured using `config.silence_healthcheck = "/up"` in Rails.
+    class SilenceRequest
+      def initialize(app, path:)
+        @app, @path = app, path
+      end
+
+      def call(env)
+        if env["PATH_INFO"] == @path
+          Rails.logger.silence { @app.call(env) }
+        else
+          @app.call(env)
+        end
+      end
+    end
+  end
+end

railties/test/commands/middleware_test.rb

@@ -196,10 +196,10 @@ def app
     assert_includes middleware, "ActionDispatch::AssumeSSL"
   end
 
-  test "ActionDispatch::SSL is present when force_ssl is set" do
-    add_to_config "config.force_ssl = true"
+  test "silence healthcheck" do
+    add_to_config "config.silence_healthcheck_path = '/up'"
     boot!
-    assert_includes middleware, "ActionDispatch::SSL"
+    assert_includes middleware, "Rails::Rack::SilenceRequest"
   end
 
   test "ActionDispatch::SSL is configured with options when given" do

railties/test/rack_silence_request_test.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "rack/test"
+require "minitest/mock"
+
+class RackSilenceRequestTest < ActiveSupport::TestCase
+  test "silence request only to specific path" do
+    mock_logger = Minitest::Mock.new
+    mock_logger.expect :silence, nil
+
+    app = Rails::Rack::SilenceRequest.new(lambda { |env| [200, env, "app"] }, path: "/up")
+
+    Rails.stub(:logger, mock_logger) do
+      app.call(Rack::MockRequest.env_for("http://example.com/up"))
+      app.call(Rack::MockRequest.env_for("http://example.com/down"))
+    end
+
+    assert mock_logger.verify
+  end
+end