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Use preferred protocol first when resolving hostname #728

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merged 5 commits into from
Jan 5, 2021
Merged

Use preferred protocol first when resolving hostname #728

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5487581
Use preferred protocol first when resolving hostname
yegle Jan 3, 2021
923274a
Use example.com hostname in test.
yegle Jan 4, 2021
d08e1b0
Inline LookupIP function call.
yegle Jan 5, 2021
5b10683
Remove unused struct.
yegle Jan 5, 2021
f44254d
Make full use of named return variables and simplify the logic.
yegle Jan 5, 2021
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81 changes: 35 additions & 46 deletions prober/utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,8 +26,13 @@ import (
"github.com/prometheus/client_golang/prometheus"
)

var protocolToGauge = map[string]float64{
"ip4": 4,
"ip6": 6,
}

// Returns the IP for the IPProtocol and lookup time.
func chooseProtocol(ctx context.Context, IPProtocol string, fallbackIPProtocol bool, target string, registry *prometheus.Registry, logger log.Logger) (ip *net.IPAddr, lookupTime float64, err error) {
func chooseProtocol(ctx context.Context, IPProtocol string, fallbackIPProtocol bool, target string, registry *prometheus.Registry, logger log.Logger) (ip *net.IPAddr, lookupTime float64, returnerr error) {
var fallbackProtocol string
probeDNSLookupTimeSeconds := prometheus.NewGauge(prometheus.GaugeOpts{
Name: "probe_dns_lookup_time_seconds",
Expand All @@ -54,64 +59,48 @@ func chooseProtocol(ctx context.Context, IPProtocol string, fallbackIPProtocol b
IPProtocol = "ip4"
fallbackProtocol = "ip6"
}
var usedProtocol string

level.Info(logger).Log("msg", "Resolving target address", "ip_protocol", IPProtocol)
resolveStart := time.Now()

defer func() {
lookupTime = time.Since(resolveStart).Seconds()
probeDNSLookupTimeSeconds.Add(lookupTime)
if usedProtocol != "" {
probeIPProtocolGauge.Set(protocolToGauge[usedProtocol])
}
if ip != nil {
probeIPAddrHash.Set(ipHash(ip.IP))
}
}()

resolver := &net.Resolver{}
ips, err := resolver.LookupIPAddr(ctx, target)
if err != nil {
level.Error(logger).Log("msg", "Resolution with IP protocol failed", "err", err)
return nil, 0.0, err
}

// Return the IP in the requested protocol.
var fallback *net.IPAddr
for _, ip := range ips {
switch IPProtocol {
case "ip4":
if ip.IP.To4() != nil {
level.Info(logger).Log("msg", "Resolved target address", "ip", ip.String())
probeIPProtocolGauge.Set(4)
probeIPAddrHash.Set(ipHash(ip.IP))
return &ip, lookupTime, nil
}

// ip4 as fallback
fallback = &ip

case "ip6":
if ip.IP.To4() == nil {
level.Info(logger).Log("msg", "Resolved target address", "ip", ip.String())
probeIPProtocolGauge.Set(6)
probeIPAddrHash.Set(ipHash(ip.IP))
return &ip, lookupTime, nil
}

// ip6 as fallback
fallback = &ip
}
}

// Unable to find ip and no fallback set.
if fallback == nil || !fallbackIPProtocol {
return nil, 0.0, fmt.Errorf("unable to find ip; no fallback")
level.Info(logger).Log("msg", "Resolving target address", "ip_protocol", IPProtocol)
if ips, err := resolver.LookupIP(ctx, IPProtocol, target); err == nil {
level.Info(logger).Log("msg", "Resolved target address", "ip", ips[0].String())
usedProtocol = IPProtocol
ip = &net.IPAddr{IP: ips[0]}
return
} else if !fallbackIPProtocol {
level.Error(logger).Log("msg", "Resolution with IP protocol failed", "err", err)
returnerr = fmt.Errorf("unable to find ip; no fallback: %s", err)
return
}

// Use fallback ip protocol.
if fallbackProtocol == "ip4" {
probeIPProtocolGauge.Set(4)
} else {
probeIPProtocolGauge.Set(6)
level.Info(logger).Log("msg", "Resolving target address", "ip_protocol", fallbackProtocol)
ips, err := resolver.LookupIP(ctx, fallbackProtocol, target)
if err != nil {
// This could happen when the domain don't have A and AAAA record (e.g.
// only have MX record).
level.Error(logger).Log("msg", "Resolution with IP protocol failed", "err", err)
returnerr = fmt.Errorf("unable to find ip; exhausted fallback: %s", err)
return
}
probeIPAddrHash.Set(ipHash(fallback.IP))
level.Info(logger).Log("msg", "Resolved target address", "ip", fallback.String())
return fallback, lookupTime, nil
level.Info(logger).Log("msg", "Resolved target address", "ip", ips[0].String())
usedProtocol = fallbackProtocol
ip = &net.IPAddr{IP: ips[0]}
return
}

func ipHash(ip net.IP) float64 {
Expand Down
14 changes: 13 additions & 1 deletion prober/utils_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ import (
"math/big"
"net"
"os"
"strings"
"testing"
"time"

Expand Down Expand Up @@ -162,14 +163,25 @@ func TestChooseProtocol(t *testing.T) {
registry = prometheus.NewPedanticRegistry()

ip, _, err = chooseProtocol(ctx, "ip4", false, "ipv6.google.com", registry, logger)
if err != nil && err.Error() != "unable to find ip; no fallback" {
if err != nil && !strings.HasPrefix(err.Error(), "unable to find ip; no fallback") {
t.Error(err)
} else if err == nil {
t.Error("should set error")
}
if ip != nil {
t.Error("without fallback it should not answer")
}

registry = prometheus.NewPedanticRegistry()
ip, _, err = chooseProtocol(ctx, "ip4", true, "does-not-exist.example.com", registry, logger)
if err != nil && !strings.HasPrefix(err.Error(), "unable to find ip; exhausted fallback") {
t.Error(err)
} else if err == nil {
t.Error("should set error")
}
if ip != nil {
t.Error("with exhausted fallback it should not answer")
}
}

func checkMetrics(expected map[string]map[string]map[string]struct{}, mfs []*dto.MetricFamily, t *testing.T) {
Expand Down