Add probe_dns_target_reachable 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_target_reachable gauge which is 1 if and only if the DNS query was executed correctly, i.e., that the target host is reachable and has sent a response, and 0 otherwise. Resolves #474 Signed-off-by: Daniel Teunis <[email protected]>
prometheus · Nov 25, 2022 · 409239b · 409239b
1 parent 7554eef
commit 409239b
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Showing 2 changed files with 28 additions and 12 deletions.
diff --git a/prober/dns.go b/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",
 	})
+	probeDNSTargetReachable := prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "probe_dns_target_reachable",
+		Help: "Displays whether or not the connection to the target was established",
+	})
 
 	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(probeDNSTargetReachable)
 
 	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)))
+	probeDNSTargetReachable.Set(1)
 
 	if qt == dns.TypeSOA {
 		probeDNSSOAGauge = prometheus.NewGauge(prometheus.GaugeOpts{

diff --git a/prober/dns_test.go b/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_target_reachable": 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_target_reachable": 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_target_reachable": 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_target_reachable"] = 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_target_reachable": nil,
 	}
 
 	checkMetrics(expectedMetrics, mfs, t)