DNS SD: add srv record target and port meta labels (#7678)

* DNS SD: add srv record target and port meta labels
Signed-off-by: NJulien Pivotto <roidelapluie@inuits.eu>

discovery/dns/dns.go

@@ -35,7 +35,10 @@ import (
 const (
 	resolvConf = "/etc/resolv.conf"
 
-	dnsNameLabel = model.MetaLabelPrefix + "dns_name"
+	dnsNameLabel            = model.MetaLabelPrefix + "dns_name"
+	dnsSrvRecordPrefix      = model.MetaLabelPrefix + "dns_srv_record_"
+	dnsSrvRecordTargetLabel = dnsSrvRecordPrefix + "target"
+	dnsSrvRecordPortLabel   = dnsSrvRecordPrefix + "port"
 
 	// Constants for instrumentation.
 	namespace = "prometheus"
@@ -183,9 +186,13 @@ func (d *Discovery) refreshOne(ctx context.Context, name string, ch chan<- *targ
 	}
 
 	for _, record := range response.Answer {
-		var target model.LabelValue
+		var target, dnsSrvRecordTarget, dnsSrvRecordPort model.LabelValue
+
 		switch addr := record.(type) {
 		case *dns.SRV:
+			dnsSrvRecordTarget = model.LabelValue(addr.Target)
+			dnsSrvRecordPort = model.LabelValue(fmt.Sprintf("%d", addr.Port))
+
 			// Remove the final dot from rooted DNS names to make them look more usual.
 			addr.Target = strings.TrimRight(addr.Target, ".")
 
@@ -199,8 +206,10 @@ func (d *Discovery) refreshOne(ctx context.Context, name string, ch chan<- *targ
 			continue
 		}
 		tg.Targets = append(tg.Targets, model.LabelSet{
-			model.AddressLabel: target,
-			dnsNameLabel:       model.LabelValue(name),
+			model.AddressLabel:      target,
+			dnsNameLabel:            model.LabelValue(name),
+			dnsSrvRecordTargetLabel: dnsSrvRecordTarget,
+			dnsSrvRecordPortLabel:   dnsSrvRecordPort,
 		})
 	}
 

discovery/dns/dns_test.go

@@ -75,7 +75,12 @@ func TestDNS(t *testing.T) {
 				{
 					Source: "web.example.com.",
 					Targets: []model.LabelSet{
-						{"__address__": "192.0.2.2:80", "__meta_dns_name": "web.example.com."},
+						{
+							"__address__":                  "192.0.2.2:80",
+							"__meta_dns_name":              "web.example.com.",
+							"__meta_dns_srv_record_target": "",
+							"__meta_dns_srv_record_port":   "",
+						},
 					},
 				},
 			},
@@ -100,7 +105,12 @@ func TestDNS(t *testing.T) {
 				{
 					Source: "web.example.com.",
 					Targets: []model.LabelSet{
-						{"__address__": "[::1]:80", "__meta_dns_name": "web.example.com."},
+						{
+							"__address__":                  "[::1]:80",
+							"__meta_dns_name":              "web.example.com.",
+							"__meta_dns_srv_record_target": "",
+							"__meta_dns_srv_record_port":   "",
+						},
 					},
 				},
 			},
@@ -125,8 +135,18 @@ func TestDNS(t *testing.T) {
 				{
 					Source: "_mysql._tcp.db.example.com.",
 					Targets: []model.LabelSet{
-						{"__address__": "db1.example.com:3306", "__meta_dns_name": "_mysql._tcp.db.example.com."},
-						{"__address__": "db2.example.com:3306", "__meta_dns_name": "_mysql._tcp.db.example.com."},
+						{
+							"__address__":                  "db1.example.com:3306",
+							"__meta_dns_name":              "_mysql._tcp.db.example.com.",
+							"__meta_dns_srv_record_target": "db1.example.com.",
+							"__meta_dns_srv_record_port":   "3306",
+						},
+						{
+							"__address__":                  "db2.example.com:3306",
+							"__meta_dns_name":              "_mysql._tcp.db.example.com.",
+							"__meta_dns_srv_record_target": "db2.example.com.",
+							"__meta_dns_srv_record_port":   "3306",
+						},
 					},
 				},
 			},
@@ -150,7 +170,12 @@ func TestDNS(t *testing.T) {
 				{
 					Source: "_mysql._tcp.db.example.com.",
 					Targets: []model.LabelSet{
-						{"__address__": "db1.example.com:3306", "__meta_dns_name": "_mysql._tcp.db.example.com."},
+						{
+							"__address__":                  "db1.example.com:3306",
+							"__meta_dns_name":              "_mysql._tcp.db.example.com.",
+							"__meta_dns_srv_record_target": "db1.example.com.",
+							"__meta_dns_srv_record_port":   "3306",
+						},
 					},
 				},
 			},

docs/configuration/configuration.md

@@ -589,9 +589,11 @@ This service discovery method only supports basic DNS A, AAAA and SRV record
 queries, but not the advanced DNS-SD approach specified in
 [RFC6763](https://tools.ietf.org/html/rfc6763).
 
-During the [relabeling phase](#relabel_config), the meta label
-`__meta_dns_name` is available on each target and is set to the
-record name that produced the discovered target.
+The following meta labels are available on targets during [relabeling](#relabel_config):
+
+* `__meta_dns_name`: the record name that produced the discovered target.
+* `__meta_dns_srv_record_target`: the target field of the SRV record
+* `__meta_dns_srv_record_port`: the port field of the SRV record
 
 ```yaml
 # A list of DNS domain names to be queried.