Add hostname RPS metric collector

Signed-off-by: Lucas Thiesen <lucas.thiesen@zalando.de>

pkg/server/start.go

@@ -65,6 +65,7 @@ func NewCommandStartAdapterServer(stopCh <-chan struct{}) *cobra.Command {
 		MetricsAddress:                    ":7979",
 		ZMONTokenName:                     "zmon",
 		CredentialsDir:                    "/meta/credentials",
+		HostnameRPSMetricName:             "skipper_serve_host_duration_seconds_count",
 	}
 
 	cmd := &cobra.Command{
@@ -132,6 +133,10 @@ func NewCommandStartAdapterServer(stopCh <-chan struct{}) *cobra.Command {
 	flags.DurationVar(&o.DefaultScheduledScalingWindow, "scaling-schedule-default-scaling-window", 10*time.Minute, "Default rampup and rampdown window duration for ScalingSchedules")
 	flags.IntVar(&o.RampSteps, "scaling-schedule-ramp-steps", 10, "Number of steps used to rampup and rampdown ScalingSchedules. It's used to guarantee won't avoid reaching the max scaling due to the 10% minimum change rule.")
 	flags.StringVar(&o.DefaultTimeZone, "scaling-schedule-default-time-zone", "Europe/Berlin", "Default time zone to use for ScalingSchedules.")
+	flags.StringVar(&o.HostnameRPSMetricName, "hostname-rps-metric-name", o.HostnameRPSMetricName, ""+
+		"The name of the metric that should be used to query prometheus for RPS per hostname.")
+	flags.BoolVar(&o.HostnameRPSMetrics, "hostname-rps-metrics", o.HostnameRPSMetrics, ""+
+		"whether to enable hostname RPS metric collector or not")
 	return cmd
 }
 
@@ -218,6 +223,18 @@ func (o AdapterServerOptions) RunCustomMetricsAdapterServer(stopCh <-chan struct
 				}
 			}
 		}
+
+		// Hostname collector, like skipper's, depends on prometheus being enabled.
+		// Also, to enable hostname metric its necessary to pass the metric name that
+		// will be used. This was built this way so we can support hostname metrics to
+		// any ingress provider, e.g. Skipper, Nginx, envoy etc, in a simple way.
+		if o.HostnameRPSMetrics && o.HostnameRPSMetricName != "" {
+			hostnamePlugin, err := collector.NewHostnameCollectorPlugin(promPlugin, o.HostnameRPSMetricName)
+			collectorFactory.RegisterExternalCollector([]string{collector.HostnameMetricType}, hostnamePlugin)
+			if err != nil {
+				return fmt.Errorf("failed to register hostname collector plugin: %v", err)
+			}
+		}
 	}
 
 	if o.InfluxDBAddress != "" {
@@ -445,4 +462,8 @@ type AdapterServerOptions struct {
 	RampSteps int
 	// Default time zone to use for ScalingSchedules.
 	DefaultTimeZone string
+	// Feature flag to enable hostname rps metric collector
+	HostnameRPSMetrics bool
+	// Name of the Prometheus metric that stores RPS by hostname for Hostname RPS metrics.
+	HostnameRPSMetricName string
 }