feat: Metrics instrumentation prototype

instrumentation/base/lib/opentelemetry/instrumentation/base.rb

@@ -189,7 +189,7 @@ def infer_version
         end
       end
 
-      attr_reader :name, :version, :config, :installed, :tracer
+      attr_reader :name, :version, :config, :installed, :tracer, :meter
 
       alias installed? installed
 
@@ -205,9 +205,20 @@ def initialize(name, version, install_blk, present_blk,
         @installed = false
         @options = options
         @tracer = OpenTelemetry::Trace::Tracer.new
+        # Do we want to conditionally create a meter overall?
+        # @meter = OpenTelemetry::Metrics::Meter.new if metrics_enabled?
       end
       # rubocop:enable Metrics/ParameterLists
 
+      def metrics_enabled?
+        # We need the API as a dependency to call metrics-y things in instrumentation
+        # However, the user needs to install it separately from base, because we
+        # do not want base to rely on experimental code
+        return @metrics_enabled if defined?(@metrics_enabled)
+
+        @metrics_enabled ||= defined?(OpenTelemetry::Metrics) && @config[:send_metrics]
+      end
+
       # Install instrumentation with the given config. The present? and compatible?
       # will be run first, and install will return false if either fail. Will
       # return true if install was completed successfully.
@@ -221,6 +232,7 @@ def install(config = {})
 
         instance_exec(@config, &@install_blk)
         @tracer = OpenTelemetry.tracer_provider.tracer(name, version)
+        @meter = OpenTelemetry.meter_provider.meter(name, version: version) if metrics_enabled?
         @installed = true
       end
 

instrumentation/rack/lib/opentelemetry/instrumentation/rack/instrumentation.rb

@@ -29,8 +29,8 @@ class Instrumentation < OpenTelemetry::Instrumentation::Base
         option :untraced_requests,        default: nil,   validate: :callable
         option :response_propagators,     default: [],    validate: :array
         # This option is only valid for applications using Rack 2.0 or greater
-        option :use_rack_events,          default: true, validate: :boolean
-
+        option :use_rack_events,          default: true,  validate: :boolean
+        option :send_metrics,             default: false, validate: :boolean
         # Temporary Helper for Sinatra and ActionPack middleware to use during installation
         #
         # @example Default usage

instrumentation/rack/lib/opentelemetry/instrumentation/rack/middlewares/event_handler.rb

@@ -158,6 +158,46 @@ def untraced_request?(env)
             false
           end
 
+          # TODO: This one is long because I wanted to keep the stable semantic
+          # conventions, and (for now) emit attributes that matched the span
+          def record_http_server_request_duration_metric(span)
+            return unless metrics_enabled? && http_server_duration_histogram
+
+            # find span duration
+            # end - start / a billion to convert nanoseconds to seconds
+            duration = (span.end_timestamp - span.start_timestamp) / Float(10**9)
+            # Create attributes
+            #
+            attrs = {}
+            # pattern below goes
+            # stable convention
+            # attribute that matches rack spans (old convention)
+
+            # attrs['http.request.method']
+            attrs['http.method'] = span.attributes['http.method']
+
+            # attrs['url.scheme']
+            attrs['http.scheme'] = span.attributes['http.scheme']
+
+            # same in stable semconv
+            attrs['http.route'] = span.attributes['http.route']
+
+            # attrs['http.response.status.code']
+            attrs['http.status_code'] = span.attributes['http.status_code']
+
+            # attrs['server.address'] ???
+            # attrs['server.port'] ???
+            # span includes host and port
+            attrs['http.host'] = span.attributes['http.host']
+
+            # attrs not currently in span payload
+            # attrs['network.protocol.version']
+            # attrs['network.protocol.name']
+            attrs['error.type'] = span.status.description if span.status.code == OpenTelemetry::Trace::Status::ERROR
+
+            http_server_duration_histogram.record(duration, attributes: attrs)
+          end
+
           # https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/data-http.md#name
           #
           # recommendation: span.name(s) should be low-cardinality (e.g.,
@@ -203,6 +243,7 @@ def detach_context(request)
             token, span = request.env[OTEL_TOKEN_AND_SPAN]
             span.finish
             OpenTelemetry::Context.detach(token)
+            record_http_server_request_duration_metric(span)
           rescue StandardError => e
             OpenTelemetry.handle_error(exception: e)
           end
@@ -247,6 +288,26 @@ def tracer
             OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.tracer
           end
 
+          def metrics_enabled?
+            OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.metrics_enabled?
+          end
+
+          def meter
+            # warn if no meter?
+            return @meter if defined?(@meter)
+
+            @meter = metrics_enabled? ? OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.meter : nil
+          end
+
+          def http_server_duration_histogram
+            # Only want to make the histogram once
+            # Need to implement advice so we can update the buckets to match seconds instead of ms
+            return @http_server_duration_histogram if defined?(@http_server_duration_histogram)
+
+            @http_server_duration_histogram = nil unless meter
+            @http_server_duration_histogram = meter.create_histogram('http.server.request.duration', unit: 's', description: 'Duration of HTTP server requests.')
+          end
+
           def config
             OpenTelemetry::Instrumentation::Rack::Instrumentation.instance.config
           end