aedara/APPEALS-26087 Setup monitoring for deprecation warnings

config/initializers/deprecation_warning_subscriber.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+# @note For use in conjuction with setting `Rails.application.config.active_support.deprecation = :notify`.
+#   Whenever a “deprecation.rails” notification is published, it will dispatch the event
+#   (ActiveSupport::Notifications::Event) to method #deprecation.
+class DeprecationWarningSubscriber < ActiveSupport::Subscriber
+  APP_NAME = "caseflow"
+  SLACK_ALERT_CHANNEL = "#appeals-deprecation-alerts"
+
+  attach_to :rails
+
+  def deprecation(event)
+    emit_warning_to_application_logs(event)
+    emit_warning_to_sentry(event)
+    emit_warning_to_slack_alerts_channel(event)
+  end
+
+  private
+
+  def emit_warning_to_application_logs(event)
+    Rails.logger.warn(event.payload[:message])
+  end
+
+  def emit_warning_to_sentry(event)
+    Raven.capture_message(
+      event.payload[:message],
+      level: "warning",
+      extra: {
+        message: event.payload[:message],
+        callstack: event.payload[:callstack],
+        environment: Rails.env
+      }
+    )
+  end
+
+  def emit_warning_to_slack_alerts_channel(event)
+    slack_alert_title = "Deprecation Warning - #{APP_NAME} (#{ENV['DEPLOY_ENV']})"
+
+    SlackService
+      .new(url: ENV["SLACK_DISPATCH_ALERT_URL"])
+      .send_notification(event.payload[:message], slack_alert_title, SLACK_ALERT_CHANNEL)
+  end
+end

spec/initializers/deprecation_warning_subscriber_spec.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+describe "DeprecationWarningSubscriber" do
+  let(:rails_logger) { Rails.logger }
+  let(:slack_service) { SlackService.new(url: "dummy-url") }
+
+  before do
+    allow(Rails).to receive(:logger).and_return(rails_logger)
+    allow(rails_logger).to receive(:warn)
+
+    allow(Raven).to receive(:capture_message)
+
+    allow(SlackService).to receive(:new).with(url: anything).and_return(slack_service)
+    allow(slack_service).to receive(:send_notification)
+  end
+
+  context "when a 'deprecation.rails' event is instrumented" do
+    let(:app_name) { "caseflow" }
+    let(:deploy_env) { "test" }
+    let(:payload) { { message: "test message", callstack: "test callstack" } }
+
+    before { ActiveSupport::Notifications.instrument("deprecation.rails", payload) }
+
+    it "emits a warning to the application logs" do
+      expect(rails_logger).to have_received(:warn).with(payload[:message])
+    end
+
+    it "emits a warning to Sentry" do
+      expect(Raven).to have_received(:capture_message).with(
+        payload[:message],
+        level: "warning",
+        extra: {
+          message: payload[:message],
+          callstack: payload[:callstack],
+          environment: Rails.env
+        }
+      )
+    end
+
+    it "emits a warning to Slack channel" do
+      slack_alert_title = "Deprecation Warning - #{app_name} (#{deploy_env})"
+      expect(slack_service).to have_received(:send_notification).with(
+        payload[:message],
+        slack_alert_title,
+        "#appeals-deprecation-alerts"
+      )
+    end
+  end
+end