Add probe_dns_query_succeeded metric

Currently, one may not be able to differentiate between a query refusal
by the target and the target not responding to a query. These two cases
can have very different ramifications.

This patch adds the probe_dns_query_succeeded gauge which is 1 if and
only if the DNS query was executed correctly, i.e., that the target
host has sent a response, and 0 otherwise.

Resolves #474

Signed-off-by: Daniel Teunis <daniel@teunis.cc>

prober/dns.go

@@ -142,6 +142,10 @@ func ProbeDNS(ctx context.Context, target string, module config.Module, registry
 		Name: "probe_dns_additional_rrs",
 		Help: "Returns number of entries in the additional resource record list",
 	})
+	probeDNSQuerySucceeded := prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "probe_dns_query_succeeded",
+		Help: "Displays whether or not the query was executed successfully",
+	})
 
 	for _, lv := range []string{"resolve", "connect", "request"} {
 		probeDNSDurationGaugeVec.WithLabelValues(lv)
@@ -151,6 +155,7 @@ func ProbeDNS(ctx context.Context, target string, module config.Module, registry
 	registry.MustRegister(probeDNSAnswerRRSGauge)
 	registry.MustRegister(probeDNSAuthorityRRSGauge)
 	registry.MustRegister(probeDNSAdditionalRRSGauge)
+	registry.MustRegister(probeDNSQuerySucceeded)
 
 	qc := uint16(dns.ClassINET)
 	if module.DNS.QueryClass != "" {
@@ -274,6 +279,7 @@ func ProbeDNS(ctx context.Context, target string, module config.Module, registry
 	probeDNSAnswerRRSGauge.Set(float64(len(response.Answer)))
 	probeDNSAuthorityRRSGauge.Set(float64(len(response.Ns)))
 	probeDNSAdditionalRRSGauge.Set(float64(len(response.Extra)))
+	probeDNSQuerySucceeded.Set(1)
 
 	if qt == dns.TypeSOA {
 		probeDNSSOAGauge = prometheus.NewGauge(prometheus.GaugeOpts{

prober/dns_test.go

@@ -179,9 +179,10 @@ func TestRecursiveDNSResponse(t *testing.T) {
 				t.Fatal(err)
 			}
 			expectedResults := map[string]float64{
-				"probe_dns_answer_rrs":     2,
-				"probe_dns_authority_rrs":  0,
-				"probe_dns_additional_rrs": 0,
+				"probe_dns_answer_rrs":      2,
+				"probe_dns_authority_rrs":   0,
+				"probe_dns_additional_rrs":  0,
+				"probe_dns_query_succeeded": 1,
 			}
 			if !test.Probe.Recursion {
 				expectedResults["probe_dns_answer_rrs"] = 0
@@ -382,9 +383,10 @@ func TestAuthoritativeDNSResponse(t *testing.T) {
 				t.Fatal(err)
 			}
 			expectedResults := map[string]float64{
-				"probe_dns_answer_rrs":     1,
-				"probe_dns_authority_rrs":  2,
-				"probe_dns_additional_rrs": 3,
+				"probe_dns_answer_rrs":      1,
+				"probe_dns_authority_rrs":   2,
+				"probe_dns_additional_rrs":  3,
+				"probe_dns_query_succeeded": 1,
 			}
 			if test.Probe.QueryType == "SOA" {
 				expectedResults["probe_dns_serial"] = 1000
@@ -456,10 +458,17 @@ func TestServfailDNSResponse(t *testing.T) {
 				t.Fatal(err)
 			}
 			expectedResults := map[string]float64{
-				"probe_dns_answer_rrs":     0,
-				"probe_dns_authority_rrs":  0,
-				"probe_dns_additional_rrs": 0,
+				"probe_dns_answer_rrs":      0,
+				"probe_dns_authority_rrs":   0,
+				"probe_dns_additional_rrs":  0,
+				"probe_dns_query_succeeded": 1,
 			}
+
+			// Handle case where ProbeDNS fails before executing the query because of an invalid query type
+			if test.Probe.QueryType == "NOT_A_VALID_QUERY_TYPE" {
+				expectedResults["probe_dns_query_succeeded"] = 0
+			}
+
 			checkRegistryResults(expectedResults, mfs, t)
 		}
 	}
@@ -638,9 +647,10 @@ func TestDNSMetrics(t *testing.T) {
 				"request": {},
 			},
 		},
-		"probe_dns_answer_rrs":     nil,
-		"probe_dns_authority_rrs":  nil,
-		"probe_dns_additional_rrs": nil,
+		"probe_dns_answer_rrs":      nil,
+		"probe_dns_authority_rrs":   nil,
+		"probe_dns_additional_rrs":  nil,
+		"probe_dns_query_succeeded": nil,
 	}
 
 	checkMetrics(expectedMetrics, mfs, t)