Expose ACK rate for Semtech UDP backend per Gateway ID.

If the ChirpStack Gateway Bridge is installed on the server and
especially using Docker, there can be cases where the uplink path (GW >
CGB) works, but the downlink path (CGB > GW) fails (UDP packets never
reach the GW). By exposing the ACK rate per Gateway ID, it is possible
to add per gateway monitoring.

As the exposed ack-rate represents the last reported ack-rate by the GW,
it is also important to monitor the ack-rate count. If this value does
not increment, it could mean that the GW is no longer reporting the
ack-rate and thus the exposed ack-rate is stale.

Author: brocaar

internal/backend/semtechudp/backend.go

@@ -462,6 +462,8 @@ func (b *Backend) handlePushData(up udpPacket) error {
 		return errors.Wrap(err, "get stats error")
 	}
 	if stats != nil {
+		ackRateCounter(p.GatewayMAC).Inc()
+		ackRate(p.GatewayMAC).Set(p.Payload.Stat.ACKR)
 		b.handleStats(p.GatewayMAC, stats)
 	}
 

internal/backend/semtechudp/metrics.go

@@ -1,6 +1,7 @@
 package semtechudp
 
 import (
+	"github.com/brocaar/lorawan"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 )
@@ -25,6 +26,16 @@ var (
 		Name: "backend_semtechudp_gateway_diconnect_count",
 		Help: "The number of gateways that disconnected from the backend.",
 	})
+
+	ackr = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Name: "backend_semtechdup_gateway_ack_rate",
+		Help: "The percentage of upstream datagrams that were acknowledged.",
+	}, []string{"gateway_id"})
+
+	ackrc = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "backend_semtechudp_gateway_ack_rate_count",
+		Help: "The number of ack-rates reported.",
+	}, []string{"gateway_id"})
 )
 
 func udpWriteCounter(pt string) prometheus.Counter {
@@ -42,3 +53,11 @@ func connectCounter() prometheus.Counter {
 func disconnectCounter() prometheus.Counter {
 	return gwd
 }
+
+func ackRate(gatewayID lorawan.EUI64) prometheus.Gauge {
+	return ackr.With(prometheus.Labels{"gateway_id": gatewayID.String()})
+}
+
+func ackRateCounter(gatewayID lorawan.EUI64) prometheus.Counter {
+	return ackrc.With(prometheus.Labels{"gateway_id": gatewayID.String()})
+}