Record submission counts with OpenTelemetry counter

Replace the periodic database aggregation rake task with an
incrementing counter at submission creation time, and export metrics
via PeriodicMetricReader.

Author: theseanything

app/services/form_submission_service.rb

@@ -104,6 +104,8 @@ def create_submission_record
 
     submission.deliveries.create!(delivery_schedule: :immediate)
 
+    Metrics::SubmissionCounter.record(form_id: form.id, form_name: form.name, mode:)
+
     submission
   end
 

app/services/metrics/submission_count_service.rb

@@ -0,0 +1,44 @@
+module Metrics
+  class SubmissionCounter
+    METRIC_NAME = "SubmissionCount".freeze
+    METER_NAME = "forms-runner".freeze
+    METER_VERSION = "1.0".freeze
+
+    class << self
+      def record(form_id:, form_name:, mode:, meter_provider: OpenTelemetry.meter_provider)
+        return if mode.preview?
+
+        counter(meter_provider).add(
+          1,
+          attributes: metric_attributes(form_id:, form_name:),
+        )
+      end
+
+    private
+
+      def counter(meter_provider)
+        counters[meter_provider] ||= meter(meter_provider).create_counter(
+          METRIC_NAME,
+          unit: "1",
+          description: "Number of form submissions",
+        )
+      end
+
+      def counters
+        @counters ||= {}
+      end
+
+      def meter(meter_provider)
+        meter_provider.meter(METER_NAME, version: METER_VERSION)
+      end
+
+      def metric_attributes(form_id:, form_name:)
+        {
+          "Environment" => Settings.forms_env.downcase,
+          "FormId" => form_id.to_s,
+          "FormName" => form_name.to_s,
+        }
+      end
+    end
+  end
+end

app/services/metrics/submission_counter.rb

@@ -5,8 +5,6 @@
 
 return unless ENV["ENABLE_OTEL"] == "true"
 
-ENV["OTEL_METRICS_EXPORTER"] ||= "otlp"
-
 OpenTelemetry::SDK.configure do |c|
   instrumentation_config = { "OpenTelemetry::Instrumentation::Rack" => { untraced_endpoints: ["/up"] } }
   c.use_all(instrumentation_config)
@@ -16,6 +14,14 @@
     c.id_generator = OpenTelemetry::Propagator::XRay::IDGenerator
   end
 
+  unless ENV.fetch("OTEL_METRICS_EXPORTER", "otlp") == "none"
+    c.add_metric_reader(
+      OpenTelemetry::SDK::Metrics::Export::PeriodicMetricReader.new(
+        exporter: OpenTelemetry::Exporter::OTLP::Metrics::MetricsExporter.new,
+      ),
+    )
+  end
+
   # Disable logging for Rake tasks to avoid cluttering output
   c.logger = Logger.new(File::NULL) if Rails.const_defined?(:Rake) && Rake.application.top_level_tasks.any?
 end

config/initializers/opentelemetry.rb

@@ -102,6 +102,16 @@
       expect(log_line["submission_reference"]).to eq(reference)
     end
 
+    it "records a submission count metric" do
+      expect(Metrics::SubmissionCounter).to receive(:record).with(
+        form_id: form.id,
+        form_name: form.name,
+        mode:,
+      )
+
+      service.submit
+    end
+
     shared_examples "logging" do
       it "logs submission" do
         allow(LogEventService).to receive(:log_submit).once