feat: add option to enable granular lease metrics (#24)
Introduce a new flag that can be used to expose each DHCP lease as a specific metric. Given the high cardinality of these metrics, exposition of lease information is disabled by default. This feature takes cues from node_exporter collectors which are disabled by default, like the `processes` or `systemd` collectors for instance. Typically, high-cardinality metrics are against prometheus best-practices but for smaller networks (like home networks) these features can be quite powerful.
This commit is contained in:
Brandon Richardson
GitHub
parent
08fab8ede7
commit
e3caa1dcf7
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@ -1,6 +1,6 @@
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# dnsmasq exporter
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[](https://travis-ci.org/google/dnsmasq_exporter)
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[](https://github.com/google/dnsmasq_exporter/actions)
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dnsmasq_exporter is an exporter for [Prometheus](https://prometheus.io/),
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allowing you to monitor/alert on the number of DHCP leases and various DNS
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@ -32,6 +32,7 @@ systemctl enable --now dnsmasq_exporter
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```
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### Alternative usage
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```shell
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docker build -t dnsmasq_exporter .
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docker run --restart=unless-stopped --net=host dnsmasq_exporter
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130
dnsmasq.go
130
dnsmasq.go
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@ -38,6 +38,9 @@ var (
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"localhost:9153",
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"listen address")
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exposeLeases = flag.Bool("expose_leases",
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false,
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"expose dnsmasq leases as metrics (high cardinality)")
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leasesPath = flag.String("leases_path",
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"/var/lib/misc/dnsmasq.leases",
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"path to the dnsmasq leases file")
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@ -102,6 +105,16 @@ var (
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),
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}
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// individual lease metrics have high cardinality and are thus disabled by
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// default, unless enabled with the -expose_leases flag
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leaseMetrics = prometheus.NewGaugeVec(
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prometheus.GaugeOpts{
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Name: "dnsmasq_lease_expiry",
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Help: "Expiry time for active DHCP leases",
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},
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[]string{"mac_addr", "ip_addr", "computer_name", "client_id"},
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)
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leases = prometheus.NewGauge(prometheus.GaugeOpts{
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Name: "dnsmasq_leases",
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Help: "Number of DHCP leases handed out",
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@ -116,6 +129,7 @@ func init() {
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prometheus.MustRegister(g)
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}
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prometheus.MustRegister(leases)
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prometheus.MustRegister(leaseMetrics)
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prometheus.MustRegister(version.NewCollector("dnsmasq_exporter"))
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}
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@ -128,10 +142,19 @@ func init() {
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// dig +short chaos txt cachesize.bind
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type server struct {
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promHandler http.Handler
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dnsClient *dns.Client
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dnsmasqAddr string
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leasesPath string
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promHandler http.Handler
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dnsClient *dns.Client
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dnsmasqAddr string
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leasesPath string
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exposeLeases bool
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}
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type lease struct {
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expiry uint64
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macAddress string
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ipAddress string
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computerName string
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clientId string
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}
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func question(name string) dns.Question {
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@ -142,6 +165,68 @@ func question(name string) dns.Question {
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}
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}
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func parseLease(line string) (*lease, error) {
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arr := strings.Fields(line)
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if got, want := len(arr), 5; got != want {
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return nil, fmt.Errorf("illegal lease: expected %d fields, got %d", want, got)
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}
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expires, err := strconv.ParseUint(arr[0], 10, 64)
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if err != nil {
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return nil, err
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}
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return &lease{
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expiry: expires,
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macAddress: arr[1],
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ipAddress: arr[2],
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computerName: arr[3],
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clientId: arr[4],
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}, nil
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}
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// Read the DHCP lease file with the given path and return a list of leases.
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//
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// The format of the DHCP lease file written by dnsmasq is not formally
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// documented in the dnsmasq manual but the format has been described in the
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// mailing list:
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//
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// - https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2006q2/000733.html
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// - https://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2016q2/010595.html
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//
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// The DHCP lease file is written to by lease_update_file() in
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// src/lease.c, and is read by lease_init().
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func readLeaseFile(path string) ([]lease, error) {
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f, err := os.Open(path)
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if err != nil {
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if os.IsNotExist(err) {
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// ignore
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return []lease{}, nil
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}
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return nil, err
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}
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defer f.Close()
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scanner := bufio.NewScanner(f)
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activeLeases := []lease{}
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for scanner.Scan() {
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activeLease, err := parseLease(scanner.Text())
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if err != nil {
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return nil, err
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}
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activeLeases = append(activeLeases, *activeLease)
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}
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if err := scanner.Err(); err != nil {
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return nil, err
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}
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return activeLeases, nil
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}
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func (s *server) metrics(w http.ResponseWriter, r *http.Request) {
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var eg errgroup.Group
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@ -207,26 +292,24 @@ func (s *server) metrics(w http.ResponseWriter, r *http.Request) {
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})
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eg.Go(func() error {
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f, err := os.Open(s.leasesPath)
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activeLeases, err := readLeaseFile(s.leasesPath)
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if err != nil {
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if os.IsNotExist(err) {
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// ignore
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leases.Set(0)
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return nil
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return err
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}
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leases.Set(float64(len(activeLeases)))
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if s.exposeLeases {
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for _, activeLease := range activeLeases {
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leaseMetrics.With(prometheus.Labels{
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"mac_addr": activeLease.macAddress,
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"ip_addr": activeLease.ipAddress,
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"computer_name": activeLease.computerName,
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"client_id": activeLease.clientId,
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}).Set(float64(activeLease.expiry))
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}
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log.Println("warn: could not open leases file:", err)
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return err
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}
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defer f.Close()
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scanner := bufio.NewScanner(f)
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var lines float64
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for scanner.Scan() {
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lines++
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}
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if err := scanner.Err(); err != nil {
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return err
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}
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leases.Set(lines)
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return nil
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})
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@ -245,8 +328,9 @@ func main() {
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dnsClient: &dns.Client{
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SingleInflight: true,
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},
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dnsmasqAddr: *dnsmasqAddr,
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leasesPath: *leasesPath,
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dnsmasqAddr: *dnsmasqAddr,
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leasesPath: *leasesPath,
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exposeLeases: *exposeLeases,
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}
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http.HandleFunc(*metricsPath, s.metrics)
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http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
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@ -65,8 +65,9 @@ func TestDnsmasqExporter(t *testing.T) {
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dnsClient: &dns.Client{
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SingleInflight: true,
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},
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dnsmasqAddr: "localhost:" + port,
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leasesPath: "testdata/dnsmasq.leases",
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dnsmasqAddr: "localhost:" + port,
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leasesPath: "testdata/dnsmasq.leases",
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exposeLeases: false,
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}
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t.Run("first", func(t *testing.T) {
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@ -121,6 +122,34 @@ func TestDnsmasqExporter(t *testing.T) {
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}
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})
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t.Run("should not expose lease information when disabled", func(t *testing.T) {
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metrics := fetchMetrics(t, s)
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for key, _ := range metrics {
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if strings.Contains(key, "dnsmasq_lease_expiry") {
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t.Errorf("lease information should not be exposed when disabled: %v", key)
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}
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}
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})
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s.exposeLeases = true
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t.Run("with high-cardinality lease metrics enabled", func(t *testing.T) {
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metrics := fetchMetrics(t, s)
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want := map[string]string{
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"dnsmasq_leases": "2",
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"dnsmasq_cachesize": "666",
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"dnsmasq_hits": "5",
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"dnsmasq_misses": "1",
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"dnsmasq_lease_expiry{client_id=\"00:00:00:00:00:00\",computer_name=\"host-1\",ip_addr=\"10.10.10.10\",mac_addr=\"00:00:00:00:00:00\"}": "1.625595932e+09",
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"dnsmasq_lease_expiry{client_id=\"00:00:00:00:00:01\",computer_name=\"host-2\",ip_addr=\"10.10.10.11\",mac_addr=\"00:00:00:00:00:01\"}": "0",
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}
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for key, val := range want {
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if got, want := metrics[key], val; got != want {
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t.Errorf("metric %q: got %q, want %q", key, got, want)
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}
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}
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})
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s.leasesPath = "testdata/dnsmasq.leases.does.not.exists"
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t.Run("without leases file", func(t *testing.T) {
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@ -128,7 +157,7 @@ func TestDnsmasqExporter(t *testing.T) {
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want := map[string]string{
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"dnsmasq_leases": "0",
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"dnsmasq_cachesize": "666",
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"dnsmasq_hits": "4",
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"dnsmasq_hits": "6",
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"dnsmasq_misses": "1",
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}
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for key, val := range want {
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4
testdata/dnsmasq.leases
vendored
4
testdata/dnsmasq.leases
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lease1
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lease2
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1625595932 00:00:00:00:00:00 10.10.10.10 host-1 00:00:00:00:00:00
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0 00:00:00:00:00:01 10.10.10.11 host-2 00:00:00:00:00:01
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