From bc6806aa896177dbf919c03abc19d80b633cfbdc Mon Sep 17 00:00:00 2001
From: Georg Gadinger <nilsding@nilsding.org>
Date: Mon, 13 Feb 2023 20:13:32 +0100
Subject: [PATCH 1/6] initial metrics

---
 Gemfile                                     |  2 ++
 Gemfile.lock                                |  2 ++
 app/controllers/inbox_controller.rb         | 11 +++++++
 app/controllers/metrics_controller.rb       | 17 ++++++++++
 config/routes.rb                            |  3 ++
 lib/retrospring/metrics.rb                  | 36 +++++++++++++++++++++
 lib/use_case/question/create.rb             | 11 +++++++
 lib/use_case/question/create_followers.rb   | 11 +++++++
 spec/controllers/metrics_controller_spec.rb | 16 +++++++++
 9 files changed, 109 insertions(+)
 create mode 100644 app/controllers/metrics_controller.rb
 create mode 100644 lib/retrospring/metrics.rb
 create mode 100644 spec/controllers/metrics_controller_spec.rb

diff --git a/Gemfile b/Gemfile
index 1b14f588..fb0afd81 100644
--- a/Gemfile
+++ b/Gemfile
@@ -117,3 +117,5 @@ gem "openssl", "~> 3.1"
 
 # mail 2.8.0 breaks sendmail usage: https://github.com/mikel/mail/issues/1538
 gem "mail", "~> 2.7.1"
+
+gem "prometheus-client", "~> 4.0"
diff --git a/Gemfile.lock b/Gemfile.lock
index 8fd5df6d..f7d3b596 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -279,6 +279,7 @@ GEM
     pg (1.4.5)
     pghero (3.1.0)
       activerecord (>= 6)
+    prometheus-client (4.0.0)
     public_suffix (4.0.7)
     puma (6.1.0)
       nio4r (~> 2.0)
@@ -522,6 +523,7 @@ DEPENDENCIES
   openssl (~> 3.1)
   pg
   pghero
+  prometheus-client (~> 4.0)
   puma
   pundit (~> 2.3)
   questiongenerator (~> 1.1)
diff --git a/app/controllers/inbox_controller.rb b/app/controllers/inbox_controller.rb
index d849dafc..16c47099 100644
--- a/app/controllers/inbox_controller.rb
+++ b/app/controllers/inbox_controller.rb
@@ -37,6 +37,7 @@ class InboxController < ApplicationController
                                 user:                current_user)
 
     inbox = Inbox.create!(user: current_user, question_id: question.id, new: true)
+    increment_metric
 
     respond_to do |format|
       format.turbo_stream do
@@ -85,4 +86,14 @@ class InboxController < ApplicationController
     # using .dup to not modify @inbox -- useful in tests
     @inbox&.dup&.update_all(new: false) # rubocop:disable Rails/SkipsModelValidations
   end
+
+  def increment_metric
+    Retrospring::Metrics::QUESTIONS_ASKED.increment(
+      labels: {
+        anonymous: true,
+        followers: false,
+        generated: true,
+      }
+    )
+  end
 end
diff --git a/app/controllers/metrics_controller.rb b/app/controllers/metrics_controller.rb
new file mode 100644
index 00000000..dae673a6
--- /dev/null
+++ b/app/controllers/metrics_controller.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require "prometheus/client/formats/text"
+
+class MetricsController < ActionController::API
+  include ActionController::MimeResponds
+
+  def show
+    render plain: metrics
+  end
+
+  private
+
+  def metrics
+    Prometheus::Client::Formats::Text.marshal(Prometheus::Client.registry)
+  end
+end
diff --git a/config/routes.rb b/config/routes.rb
index 744a8d83..fc210a32 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -49,6 +49,9 @@ Rails.application.routes.draw do
   get "/linkfilter", to: "link_filter#index", as: :linkfilter
   get "/manifest.json", to: "manifests#show", as: :webapp_manifest
 
+  # TODO: limit this endpoint
+  get "/metrics", to: "metrics#show"
+
   # Devise routes
   devise_for :users, path: "user", skip: %i[sessions registrations]
   as :user do
diff --git a/lib/retrospring/metrics.rb b/lib/retrospring/metrics.rb
new file mode 100644
index 00000000..0072fd81
--- /dev/null
+++ b/lib/retrospring/metrics.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module Retrospring
+  module Metrics
+    PROMETHEUS = Prometheus::Client.registry
+
+    # avoid re-registering metrics to make autoreloader happy:
+    class << self
+      %i[counter gauge histogram summary].each do |meth|
+        define_method meth do |name, *args, **kwargs|
+          PROMETHEUS.public_send(meth, name, *args, **kwargs)
+        rescue Prometheus::Client::Registry::AlreadyRegisteredError
+          raise unless Rails.env.development?
+
+          PROMETHEUS.unregister name
+          retry
+        end
+      end
+    end
+
+    VERSION_INFO = gauge(
+      :retrospring_version_info,
+      docstring:     "Information about the currently running version",
+      labels:        [:version],
+      preset_labels: {
+        version: Retrospring::Version.to_s,
+      }
+    ).tap { _1.set 1 }
+
+    QUESTIONS_ASKED = counter(
+      :retrospring_questions_asked_total,
+      docstring: "How many questions got asked",
+      labels:    %i[anonymous followers generated]
+    )
+  end
+end
diff --git a/lib/use_case/question/create.rb b/lib/use_case/question/create.rb
index 5cc8f174..a7c1345d 100644
--- a/lib/use_case/question/create.rb
+++ b/lib/use_case/question/create.rb
@@ -18,6 +18,7 @@ module UseCase
         return if filtered?(question)
 
         increment_asked_count
+        increment_metric
 
         inbox = ::Inbox.create!(user: target_user, question:, new: true)
         notify(inbox)
@@ -92,6 +93,16 @@ module UseCase
         source_user.save
       end
 
+      def increment_metric
+        Retrospring::Metrics::QUESTIONS_ASKED.increment(
+          labels: {
+            anonymous:,
+            followers: false,
+            generated: false,
+          }
+        )
+      end
+
       def filtered?(question)
         target_user.mute_rules.any? { |rule| rule.applies_to? question } ||
           (anonymous && AnonymousBlock.where(identifier: question.author_identifier, user_id: [target_user.id, nil]).any?) ||
diff --git a/lib/use_case/question/create_followers.rb b/lib/use_case/question/create_followers.rb
index 21c2e89d..a6bddb0f 100644
--- a/lib/use_case/question/create_followers.rb
+++ b/lib/use_case/question/create_followers.rb
@@ -17,6 +17,7 @@ module UseCase
         )
 
         increment_asked_count
+        increment_metric
 
         QuestionWorker.perform_async(source_user_id, question.id)
 
@@ -33,6 +34,16 @@ module UseCase
         source_user.save
       end
 
+      def increment_metric
+        Retrospring::Metrics::QUESTIONS_ASKED.increment(
+          labels: {
+            anonymous: false,
+            followers: true,
+            generated: false,
+          }
+        )
+      end
+
       def source_user
         @source_user ||= ::User.find(source_user_id)
       end
diff --git a/spec/controllers/metrics_controller_spec.rb b/spec/controllers/metrics_controller_spec.rb
new file mode 100644
index 00000000..c278e308
--- /dev/null
+++ b/spec/controllers/metrics_controller_spec.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe MetricsController, type: :controller do
+  describe "#show" do
+    subject { get :show }
+
+    it "returns the metrics" do
+      # ensure we have at least a metric set
+      Retrospring::Metrics::VERSION_INFO.set 1
+
+      expect(subject.body).to include "retrospring_version_info"
+    end
+  end
+end

From 9fadeea3fe4bf59491950e36aeb3dadeeff7ee11 Mon Sep 17 00:00:00 2001
From: Georg Gadinger <nilsding@nilsding.org>
Date: Mon, 13 Feb 2023 20:14:20 +0100
Subject: [PATCH 2/6] rubodog

---
 app/controllers/inbox_controller.rb       | 2 +-
 lib/use_case/question/create.rb           | 4 ++--
 lib/use_case/question/create_followers.rb | 6 +++---
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/app/controllers/inbox_controller.rb b/app/controllers/inbox_controller.rb
index 16c47099..f6a1aff2 100644
--- a/app/controllers/inbox_controller.rb
+++ b/app/controllers/inbox_controller.rb
@@ -5,7 +5,7 @@ class InboxController < ApplicationController
 
   after_action :mark_inbox_entries_as_read, only: %i[show]
 
-  def show # rubocop:disable Metrics/MethodLength, Metrics/AbcSize
+  def show # rubocop:disable Metrics/MethodLength
     find_author
     find_inbox_entries
 
diff --git a/lib/use_case/question/create.rb b/lib/use_case/question/create.rb
index a7c1345d..17987a1d 100644
--- a/lib/use_case/question/create.rb
+++ b/lib/use_case/question/create.rb
@@ -27,8 +27,8 @@ module UseCase
           status:   201,
           resource: question,
           extra:    {
-            inbox:
-          }
+            inbox:,
+          },
         }
       end
 
diff --git a/lib/use_case/question/create_followers.rb b/lib/use_case/question/create_followers.rb
index a6bddb0f..04fe3844 100644
--- a/lib/use_case/question/create_followers.rb
+++ b/lib/use_case/question/create_followers.rb
@@ -9,9 +9,9 @@ module UseCase
 
       def call
         question = ::Question.create!(
-          content:             content,
+          content:,
           author_is_anonymous: false,
-          author_identifier:   author_identifier,
+          author_identifier:,
           user:                source_user,
           direct:              false
         )
@@ -23,7 +23,7 @@ module UseCase
 
         {
           status:   201,
-          resource: question
+          resource: question,
         }
       end
 

From c338a0c8cc889385dc33656fb730c673e51369c3 Mon Sep 17 00:00:00 2001
From: Georg Gadinger <nilsding@nilsding.org>
Date: Mon, 13 Feb 2023 20:36:15 +0100
Subject: [PATCH 3/6] add prometheus initialiser

this ensures it works great in multi-process setups (like with puma)
---
 config/initializers/prometheus.rb | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 config/initializers/prometheus.rb

diff --git a/config/initializers/prometheus.rb b/config/initializers/prometheus.rb
new file mode 100644
index 00000000..7d86c92f
--- /dev/null
+++ b/config/initializers/prometheus.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+return if Rails.env.test? # no need for the direct file store in testing
+
+require "prometheus/client/data_stores/direct_file_store"
+
+Rails.application.config.before_configuration do
+  dir = Rails.root.join("tmp/prometheus_metrics")
+  FileUtils.mkdir_p dir
+
+  Prometheus::Client.config.data_store = Prometheus::Client::DataStores::DirectFileStore.new(dir:)
+end
+
+Rails.application.config.after_initialize do
+  # ensure the version metric is populated
+  Retrospring::Metrics::VERSION_INFO
+end

From 64adbb5707ddd5a97b06c2d77f5d5ec9f9b438f5 Mon Sep 17 00:00:00 2001
From: Georg Gadinger <nilsding@nilsding.org>
Date: Mon, 13 Feb 2023 21:53:40 +0100
Subject: [PATCH 4/6] allow /metrics to be reached from private subnets only

this commit is not approved by the IPv6 crowd.  patches welcome
---
 config/routes.rb                           |  5 +-
 lib/constraints/local_network.rb           | 22 +++++++++
 spec/lib/constraints/local_network_spec.rb | 53 ++++++++++++++++++++++
 3 files changed, 78 insertions(+), 2 deletions(-)
 create mode 100644 lib/constraints/local_network.rb
 create mode 100644 spec/lib/constraints/local_network_spec.rb

diff --git a/config/routes.rb b/config/routes.rb
index fc210a32..8f485cb7 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -49,8 +49,9 @@ Rails.application.routes.draw do
   get "/linkfilter", to: "link_filter#index", as: :linkfilter
   get "/manifest.json", to: "manifests#show", as: :webapp_manifest
 
-  # TODO: limit this endpoint
-  get "/metrics", to: "metrics#show"
+  constraints(Constraints::LocalNetwork) do
+    get "/metrics", to: "metrics#show"
+  end
 
   # Devise routes
   devise_for :users, path: "user", skip: %i[sessions registrations]
diff --git a/lib/constraints/local_network.rb b/lib/constraints/local_network.rb
new file mode 100644
index 00000000..2db324a5
--- /dev/null
+++ b/lib/constraints/local_network.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module Constraints
+  module LocalNetwork
+    module_function
+
+    SUBNETS = %w[
+      10.0.0.0/8
+      127.0.0.0/8
+      172.16.0.0/12
+      192.168.0.0/16
+    ].map { IPAddr.new(_1) }.freeze
+
+    def matches?(request)
+      SUBNETS.find do |net|
+        net.include? request.remote_ip
+      rescue
+        false
+      end
+    end
+  end
+end
diff --git a/spec/lib/constraints/local_network_spec.rb b/spec/lib/constraints/local_network_spec.rb
new file mode 100644
index 00000000..88326ccb
--- /dev/null
+++ b/spec/lib/constraints/local_network_spec.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Constraints::LocalNetwork do
+  describe ".matches?" do
+    let(:request) { double("Rack::Request", remote_ip:) }
+
+    subject { described_class.matches?(request) }
+
+    context "with a private address from the 10.0.0.0/8 range" do
+      let(:remote_ip) { "10.0.2.100" }
+
+      it { is_expected.to be_truthy }
+    end
+
+    context "with a private address from the 127.0.0.0/8 range" do
+      let(:remote_ip) { "127.0.0.1" }
+
+      it { is_expected.to be_truthy }
+    end
+
+    context "with a private address from the 172.16.0.0/12 range" do
+      let(:remote_ip) { "172.31.33.7" }
+
+      it { is_expected.to be_truthy }
+    end
+
+    context "with a private address from the 192.168.0.0/16 range" do
+      let(:remote_ip) { "192.168.123.45" }
+
+      it { is_expected.to be_truthy }
+    end
+
+    context "with a non-private/loopback address" do
+      let(:remote_ip) { "193.186.6.83" }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context "with some fantasy address" do
+      let(:remote_ip) { "fe80:3::1ff:fe23:4567:890a" }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context "with an actual invalid address" do
+      let(:remote_ip) { "herbert" }
+
+      it { is_expected.to be_falsey }
+    end
+  end
+end

From b937a10096e008e741fa6283f7fab50898cf7b3a Mon Sep 17 00:00:00 2001
From: Georg Gadinger <nilsding@nilsding.org>
Date: Mon, 13 Feb 2023 22:24:52 +0100
Subject: [PATCH 5/6] add some more metrics for answers and comments

---
 app/models/user.rb         |  4 ++++
 lib/retrospring/metrics.rb | 12 +++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/app/models/user.rb b/app/models/user.rb
index 6370ed01..725582ef 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -115,6 +115,8 @@ class User < ApplicationRecord # rubocop:disable Metrics/ClassLength
     raise Errors::AnsweringSelfBlockedOther if self.blocking?(question.user)
     # rubocop:enable Style/RedundantSelf
 
+    Retrospring::Metrics::QUESTIONS_ANSWERED.increment
+
     Answer.create!(content:, user: self, question:)
   end
 
@@ -128,6 +130,8 @@ class User < ApplicationRecord # rubocop:disable Metrics/ClassLength
     raise Errors::CommentingOtherBlockedSelf if answer.user.blocking?(self)
     # rubocop:enable Style/RedundantSelf
 
+    Retrospring::Metrics::COMMENTS_CREATED.increment
+
     Comment.create!(user: self, answer:, content:)
   end
 
diff --git a/lib/retrospring/metrics.rb b/lib/retrospring/metrics.rb
index 0072fd81..7259f33f 100644
--- a/lib/retrospring/metrics.rb
+++ b/lib/retrospring/metrics.rb
@@ -4,7 +4,7 @@ module Retrospring
   module Metrics
     PROMETHEUS = Prometheus::Client.registry
 
-    # avoid re-registering metrics to make autoreloader happy:
+    # avoid re-registering metrics to make autoreloader happy during dev:
     class << self
       %i[counter gauge histogram summary].each do |meth|
         define_method meth do |name, *args, **kwargs|
@@ -32,5 +32,15 @@ module Retrospring
       docstring: "How many questions got asked",
       labels:    %i[anonymous followers generated]
     )
+
+    QUESTIONS_ANSWERED = counter(
+      :retrospring_questions_answered_total,
+      docstring: "How many questions got answered"
+    )
+
+    COMMENTS_CREATED = counter(
+      :retrospring_comments_created_total,
+      docstring: "How many comments got created"
+    )
   end
 end

From 8a055341c8de09214789ec51c4c68f1e2f92ade2 Mon Sep 17 00:00:00 2001
From: Georg Gadinger <nilsding@nilsding.org>
Date: Tue, 14 Feb 2023 05:30:40 +0100
Subject: [PATCH 6/6] add metrics for sidekiq

---
 app/controllers/metrics_controller.rb       | 24 ++++++++++++++-
 lib/retrospring/metrics.rb                  | 33 +++++++++++++++++++++
 spec/controllers/metrics_controller_spec.rb |  3 --
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/app/controllers/metrics_controller.rb b/app/controllers/metrics_controller.rb
index dae673a6..257b8b7e 100644
--- a/app/controllers/metrics_controller.rb
+++ b/app/controllers/metrics_controller.rb
@@ -6,12 +6,34 @@ class MetricsController < ActionController::API
   include ActionController::MimeResponds
 
   def show
+    fetch_sidekiq_metrics
+
     render plain: metrics
   end
 
   private
 
+  SIDEKIQ_STATS_METHODS = %i[
+    processed
+    failed
+    scheduled_size
+    retry_size
+    dead_size
+    processes_size
+  ].freeze
+
+  def fetch_sidekiq_metrics
+    stats = Sidekiq::Stats.new
+    SIDEKIQ_STATS_METHODS.each do |key|
+      Retrospring::Metrics::SIDEKIQ[key].set stats.public_send(key)
+    end
+
+    stats.queues.each do |queue, value|
+      Retrospring::Metrics::SIDEKIQ[:queue_enqueued].set value, labels: { queue: }
+    end
+  end
+
   def metrics
-    Prometheus::Client::Formats::Text.marshal(Prometheus::Client.registry)
+    Prometheus::Client::Formats::Text.marshal(Retrospring::Metrics::PROMETHEUS)
   end
 end
diff --git a/lib/retrospring/metrics.rb b/lib/retrospring/metrics.rb
index 7259f33f..7c52dcb6 100644
--- a/lib/retrospring/metrics.rb
+++ b/lib/retrospring/metrics.rb
@@ -42,5 +42,38 @@ module Retrospring
       :retrospring_comments_created_total,
       docstring: "How many comments got created"
     )
+
+    # metrics from Sidekiq::Stats.new
+    SIDEKIQ = {
+      processed:      gauge(
+        :sidekiq_processed,
+        docstring: "Number of jobs processed by Sidekiq"
+      ),
+      failed:         gauge(
+        :sidekiq_failed,
+        docstring: "Number of jobs that failed"
+      ),
+      scheduled_size: gauge(
+        :sidekiq_scheduled_jobs,
+        docstring: "Number of jobs that are enqueued"
+      ),
+      retry_size:     gauge(
+        :sidekiq_retried_jobs,
+        docstring: "Number of jobs that are being retried"
+      ),
+      dead_size:      gauge(
+        :sidekiq_dead_jobs,
+        docstring: "Number of jobs that are dead"
+      ),
+      processes_size: gauge(
+        :sidekiq_processes,
+        docstring: "Number of active Sidekiq processes"
+      ),
+      queue_enqueued: gauge(
+        :sidekiq_queues_enqueued,
+        docstring: "Number of enqueued jobs per queue",
+        labels:    %i[queue]
+      ),
+    }.freeze
   end
 end
diff --git a/spec/controllers/metrics_controller_spec.rb b/spec/controllers/metrics_controller_spec.rb
index c278e308..89f4316e 100644
--- a/spec/controllers/metrics_controller_spec.rb
+++ b/spec/controllers/metrics_controller_spec.rb
@@ -7,9 +7,6 @@ describe MetricsController, type: :controller do
     subject { get :show }
 
     it "returns the metrics" do
-      # ensure we have at least a metric set
-      Retrospring::Metrics::VERSION_INFO.set 1
-
       expect(subject.body).to include "retrospring_version_info"
     end
   end