Add device filter flags to arp collector

Allow filtering APR entries based on device. Useful for ignoring
entries for network namespaces (containers).

Signed-off-by: Ben Kochie <superq@gmail.com>

CHANGELOG.md

@@ -6,6 +6,7 @@
 * [BUGFIX]
 
 * [ENHANCEMENT] Add node_softirqs_total metric #2221
+* [ENHANCEMENT] Add device filter flags to arp collector #2254
 
 ## 1.3.1 / 2021-12-01
 

collector/arp_linux.go

@@ -25,9 +25,16 @@ import (
 
 	"github.com/go-kit/log"
 	"github.com/prometheus/client_golang/prometheus"
+	"gopkg.in/alecthomas/kingpin.v2"
+)
+
+var (
+	arpDeviceInclude = kingpin.Flag("collector.arp.device-include", "Regexp of arp devices to include (mutually exclusive to device-exclude).").String()
+	arpDeviceExclude = kingpin.Flag("collector.arp.device-exclude", "Regexp of arp devices to exclude (mutually exclusive to device-include).").String()
 )
 
 type arpCollector struct {
+	deviceFilter netDevFilter
 	entries      *prometheus.Desc
 	logger       log.Logger
 }
@@ -39,6 +46,7 @@ func init() {
 // NewARPCollector returns a new Collector exposing ARP stats.
 func NewARPCollector(logger log.Logger) (Collector, error) {
 	return &arpCollector{
+		deviceFilter: newNetDevFilter(*arpDeviceExclude, *arpDeviceInclude),
 		entries: prometheus.NewDesc(
 			prometheus.BuildFQName(namespace, "arp", "entries"),
 			"ARP entries by device",
@@ -98,6 +106,9 @@ func (c *arpCollector) Update(ch chan<- prometheus.Metric) error {
 	}
 
 	for device, entryCount := range entries {
+		if c.deviceFilter.ignored(device) {
+			continue
+		}
 		ch <- prometheus.MustNewConstMetric(
 			c.entries, prometheus.GaugeValue, float64(entryCount), device)
 	}

collector/fixtures/proc/net/arp

@@ -5,3 +5,4 @@ IP address       HW type     Flags       HW address            Mask     Device
 192.168.1.4    0x1         0x2         dd:ee:ff:aa:bb:cc     *        eth1
 192.168.1.5    0x1         0x2         ee:ff:aa:bb:cc:dd     *        eth1
 192.168.1.6    0x1         0x2         ff:aa:bb:cc:dd:ee     *        eth1
+10.0.0.1       0x1         0x2         de:ad:be:ef:00:00     *        nope

end-to-end-test.sh

@@ -109,6 +109,7 @@ fi
   --collector.textfile.directory="collector/fixtures/textfile/two_metric_files/" \
   --collector.wifi.fixtures="collector/fixtures/wifi" \
   --collector.qdisc.fixtures="collector/fixtures/qdisc/" \
+  --collector.arp.device-exclude="nope" \
   --collector.netclass.ignored-devices="(dmz|int)" \
   --collector.netclass.ignore-invalid-speed \
   --collector.bcache.priorityStats \