Revert "Use preferred protocol first when resolving hostname (prometh…

…eus#728)" This reverts commit 847b668. Signed-off-by: Julien Pivotto <[email protected]>
roidelapluie · May 28, 2021 · 54cba1b · 54cba1b
1 parent bf70c7d
commit 54cba1b
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Showing 2 changed files with 47 additions and 48 deletions.
diff --git a/prober/utils.go b/prober/utils.go
@@ -26,13 +26,8 @@ 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, returnerr error) {
+func chooseProtocol(ctx context.Context, IPProtocol string, fallbackIPProtocol bool, target string, registry *prometheus.Registry, logger log.Logger) (ip *net.IPAddr, lookupTime float64, err error) {
 	var fallbackProtocol string
 	probeDNSLookupTimeSeconds := prometheus.NewGauge(prometheus.GaugeOpts{
 		Name: "probe_dns_lookup_time_seconds",
@@ -59,48 +54,64 @@ 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{}
-
-	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 {
+	ips, err := resolver.LookupIPAddr(ctx, target)
+	if err != nil {
 		level.Error(logger).Log("msg", "Resolution with IP protocol failed", "err", err)
-		returnerr = fmt.Errorf("unable to find ip; no fallback: %s", err)
-		return
+		return nil, 0.0, err
 	}
 
-	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
+	// 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")
+	}
+
+	// Use fallback ip protocol.
+	if fallbackProtocol == "ip4" {
+		probeIPProtocolGauge.Set(4)
+	} else {
+		probeIPProtocolGauge.Set(6)
 	}
-	level.Info(logger).Log("msg", "Resolved target address", "ip", ips[0].String())
-	usedProtocol = fallbackProtocol
-	ip = &net.IPAddr{IP: ips[0]}
-	return
+	probeIPAddrHash.Set(ipHash(fallback.IP))
+	level.Info(logger).Log("msg", "Resolved target address", "ip", fallback.String())
+	return fallback, lookupTime, nil
 }
 
 func ipHash(ip net.IP) float64 {

diff --git a/prober/utils_test.go b/prober/utils_test.go
@@ -24,7 +24,6 @@ import (
 	"math/big"
 	"net"
 	"os"
-	"strings"
 	"testing"
 	"time"
 
@@ -163,25 +162,14 @@ func TestChooseProtocol(t *testing.T) {
 	registry = prometheus.NewPedanticRegistry()
 
 	ip, _, err = chooseProtocol(ctx, "ip4", false, "ipv6.google.com", registry, logger)
-	if err != nil && !strings.HasPrefix(err.Error(), "unable to find ip; no fallback") {
+	if err != nil && 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) {