Chapter 1: Instrument controller actions

lib/active_monitoring/core_extensions/action_controller.rb

@@ -0,0 +1,19 @@
+module ActiveMonitoring
+  module CoreExtensions
+    module ActionController
+      module Instrumentation
+        def process_action(*)
+          payload = {
+            controller: self.class.name,
+            action: action_name,
+            request_id: request.uuid
+          }
+          ::ActiveMonitoring::Notifications.instrument("start_processing.action_controller", payload)
+          ::ActiveMonitoring::Notifications.instrument("process_action.action_controller", payload) do
+            super
+          end
+        end
+      end
+    end
+  end
+end

lib/active_monitoring/engine.rb

@@ -1,5 +1,10 @@
+require_relative "core_extensions/action_controller"
 module ActiveMonitoring
   class Engine < ::Rails::Engine
     isolate_namespace ActiveMonitoring
+
+    ActiveSupport.on_load(:action_controller) do
+      ActionController::Base.prepend(::ActiveMonitoring::CoreExtensions::ActionController::Instrumentation)
+    end
   end
 end

spec/requests/metrics_spec.rb

@@ -1,9 +1,52 @@
 require "rails_helper"
 
 RSpec.describe "ActionController metrics", type: :request do
-  it "works" do
+  scenario "is succesful" do
     post books_path
 
-    expect(response.status).to be 200
+    expect(response).to be_successful
+    expect(response.body).to eq("ok")
+  end
+
+  scenario "Instruments start_processing.action_controller" do
+    travel_to(Time.zone.local(2020, 1, 1))
+    events = []
+    ActiveMonitoring::Notifications.subscribe("start_processing.action_controller") do |name, start, finish, id, payload|
+      events << { name: name, start: start, finish: finish, id: id, payload: payload }
+    end
+
+    post books_path
+
+    expect(events).to include(
+      a_hash_including(
+        name: "start_processing.action_controller",
+        start: Time.zone.local(2020, 1, 1),
+        finish: Time.zone.local(2020, 1, 1),
+        payload: a_hash_including(
+          request_id: response.headers["X-Request-Id"]
+        )
+      )
+    )
+  end
+
+  scenario "Instruments process_action.action_controller" do
+    travel_to(Time.zone.local(2020, 1, 1))
+    events = []
+    ActiveMonitoring::Notifications.subscribe("process_action.action_controller") do |name, start, finish, id, payload|
+      events << { name: name, start: start, finish: finish, id: id, payload: payload }
+    end
+
+    post books_path
+
+    expect(events).to include(
+      a_hash_including(
+        name: "process_action.action_controller",
+        start: Time.zone.local(2020, 1, 1),
+        finish: Time.zone.local(2020, 1, 1),
+        payload: a_hash_including(
+          request_id: response.headers["X-Request-Id"]
+        )
+      )
+    )
   end
 end