Merge pull request #140 from epimorphics/issue/139-task-prometheus-me…

…trics-update

Task: Prometheus Metrics - Update

CHANGELOG.md

@@ -1,7 +1,19 @@
 # Standard Reports UI: change log
 
-## 1.5.4 - 2024-09
-
+## Unreleased
+
+- (Jon) Updated the application exceptions controller to instrument the
+  `ActiveSupport::Notifications` for internal errors
+  [GH-139](https://github.com/epimorphics/standard-reports-ui/issues/139)
+- (Jon) Updated `config/initializers/prometheus.rb` to include the `Middleware
+  instrumentation` fix for the 0 memory bug by notifying Action Dispatch
+  subscribers on Prometheus initialise
+  [GH-139](https://github.com/epimorphics/standard-reports-ui/issues/139)
+- (Jon) Updated `config/puma.rb` to include metrics plugin and port information
+  for the metrics endpoint as environment variable, with default, to enable
+  running multiple sibling HMLR apps locally if needed without port conflicts
+  [GH-139](https://github.com/epimorphics/standard-reports-ui/issues/139)
+- (Jon) Updated the `lr_common_styles` gem to the latest 1.9.9 patch release.
 - (Jon) Moved all mirrored configuration settings from individual environments
   into the application configuration to reduce the need to manage multiple
   sources of truth

Gemfile.lock

@@ -367,7 +367,7 @@ GEM
       json
       lograge
       railties
-    lr_common_styles (1.9.8)
+    lr_common_styles (1.9.9)
       bootstrap-sass (~> 3.4.0)
       font-awesome-rails (~> 4.7.0.1)
       govuk_elements_rails (~> 2.0.0)

app/controllers/application_controller.rb

@@ -27,6 +27,9 @@ def log_request_result
   # or attempt to render a generic error page if no specific error page exists
   unless Rails.application.config.consider_all_requests_local
     rescue_from StandardError do |e|
+      # Instrument ActiveSupport::Notifications for internal errors:
+      ActiveSupport::Notifications.instrument('internal_error.application', exception: e)
+      # Trigger the appropriate error handling method based on the exception
       case e.class
       when ActionController::RoutingError, ActionView::MissingTemplate
         :render404
@@ -41,10 +44,7 @@ def log_request_result
   end
 
   def handle_internal_error(exception)
-    # Notify subscribers of the internal error event and render the appropriate error page
-    # or attempt to render a generic error page if no specific error page exists
-    # unless the exception is a 404, in which case do nothing
-    instrument_internal_error(exception) unless exception.status == 404
+    # Render the appropriate error page based on the exception
     if exception.instance_of? ArgumentError
       render_error(400)
     else
@@ -118,13 +118,4 @@ def detailed_request_log(duration)
     end
   end
   # rubocop:enable Metrics/AbcSize, Metrics/MethodLength
-
-  # Notify subscriber(s) of an internal error event with the payload of the
-  # exception once done
-  # @param [Exception] exp the exception that caused the error
-  # @return [ActiveSupport::Notifications::Event] provides an object-oriented
-  # interface to the event
-  def instrument_internal_error(exception)
-    ActiveSupport::Notifications.instrument('internal_error.application', exception: exception)
-  end
 end

config/initializers/prometheus.rb

@@ -48,3 +48,7 @@
   docstring: 'Histogram of response times for API requests',
   buckets: Prometheus::Client::Histogram.exponential_buckets(start: 0.005, count: 16)
 )
+
+# Middleware instrumentation
+  # This fixes the 0 memory bug by notifying Action Dispatch subscribers on Prometheus initialise
+  ActiveSupport::Notifications.instrument('process_middleware.action_dispatch')

config/puma.rb

@@ -10,9 +10,13 @@
 min_threads_count = ENV.fetch('RAILS_MIN_THREADS', max_threads_count)
 threads min_threads_count, max_threads_count
 
-# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
-#
-port        ENV.fetch('PORT', 3000)
+# Specifies the `port` that Puma will listen on to receive requests;
+# default is 3000.
+port ENV.fetch('PORT', 3000)
+
+# Specifies the `metrics_port` that Puma will listen on to export metrics;
+# default is 9393.
+metrics_port = ENV.fetch('METRICS_PORT', 9393)
 
 # Specifies the `environment` that Puma will run in.
 #
@@ -36,9 +40,13 @@
 #
 # preload_app!
 
+# Enable the metrics plugin to export Puma's internal statistics as Prometheus metrics
+plugin :metrics
+# Bind the metric server to "url". "tcp://" is the only accepted protocol.
+metrics_url "tcp://0.0.0.0:#{metrics_port}" if Rails.env.development?
+
 # Allow puma to be restarted by `rails restart` command.
 plugin :tmp_restart
-plugin :metrics
 
 # Use a custom log formatter to emit Puma log messages in a JSON format
 log_formatter do |str|