add dnsname as separate label, use domain label consistently

The domain coming from the config is already used to indicate fetch success, which is confusing in cases where dnsname (what's in the certificate) might differ from what's in the config.

This is a breaking change, since the content of the domain label is now different.

main.go

@@ -21,9 +21,9 @@ type Config struct {
 
 var config Config
 
-func loadCertificates() ([]*x509.Certificate, string) {
+func loadCertificates() (map[string]*x509.Certificate, string) {
 	startTime := time.Now().UnixNano()
-	var certs []*x509.Certificate
+	var certs = make(map[string]*x509.Certificate)
 	var fetchMetrics = ""
 
 	for _, d := range config.Domains {
@@ -43,7 +43,7 @@ func loadCertificates() ([]*x509.Certificate, string) {
 			if resp.TLS != nil {
 				certificates := resp.TLS.PeerCertificates
 				if len(certificates) > 0 {
-					certs = append(certs, certificates[0])
+					certs[d] = certificates[0]
 					fetchMetrics += "cert_fetch_success{domain=\"" + d + "\"} 1\n"
 				} else {
 					log.Println("No certificates given for '" + d + "'!")
@@ -76,10 +76,10 @@ func renderMetricsResponse() (string, error) {
 		"# TYPE cert_fetch_duration gauge\n" +
 		"# HELP cert_fetch_success Success of the http call as a 0/1 boolean.\n" +
 		"# TYPE cert_fetch_success gauge\n" + metrics
-	for _, crt := range certs {
+	for domain, crt := range certs {
 		for _, dnsName := range crt.DNSNames {
-			res += `cert_not_before{domain="` + dnsName + `"} ` + strconv.FormatInt(crt.NotBefore.Unix(), 10) + "\n"
-			res += `cert_not_after{domain="` + dnsName + `"} ` + strconv.FormatInt(crt.NotAfter.Unix(), 10) + "\n"
+			res += `cert_not_before{domain="` + domain + `",dnsname="` + dnsName + `"} ` + strconv.FormatInt(crt.NotBefore.Unix(), 10) + "\n"
+			res += `cert_not_after{domain="` + domain + `",dnsname="` + dnsName + `"} ` + strconv.FormatInt(crt.NotAfter.Unix(), 10) + "\n"
 		}
 	}