telemetry: try guess hostname or external IP addr for metrics (#2412)

internal/registry/hostname.go

@@ -0,0 +1,67 @@
+package registry
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"os"
+	"strings"
+)
+
+func isFQDN(host string) bool {
+	return strings.Count(host, ".") > 1
+}
+
+func chooseIP(ips []net.IP) net.IP {
+	for _, ip := range ips {
+		if !ip.IsLoopback() && !ip.IsInterfaceLocalMulticast() && !ip.IsLinkLocalUnicast() && !ip.IsLinkLocalMulticast() {
+			return ip
+		}
+	}
+	return nil
+}
+
+// getViaLookup tries to lookup whether short hostname may be resolved into IP and back into a longer one
+func getViaLookup(host string) (string, error) {
+	addrs, err := net.LookupIP(host)
+	if err != nil {
+		return "", err
+	}
+	if len(addrs) == 0 {
+		return "", errors.New("address lookup failed")
+	}
+	for _, addr := range addrs {
+		hosts, err := net.LookupAddr(addr.String())
+		if err != nil {
+			continue
+		}
+		for _, h := range hosts {
+			h = strings.TrimSuffix(h, ".")
+			if isFQDN(h) {
+				return h, nil
+			}
+		}
+	}
+
+	if ip := chooseIP(addrs); ip != nil {
+		return ip.String(), nil
+	}
+	return "", errors.New("lookup failed")
+}
+
+// getHostOrIP tries to fetch a publicly accessible IP address for the current host/container
+func getHostOrIP() (string, error) {
+	host, err := os.Hostname()
+	if err != nil {
+		return "", fmt.Errorf("hostname: %w", err)
+	}
+	if isFQDN(host) {
+		return host, nil
+	}
+
+	if h, err := getViaLookup(host); err == nil {
+		return h, nil
+	}
+
+	return host, nil
+}

internal/registry/reporter.go

@@ -81,9 +81,22 @@ func getReportedServices(cfg *config.Config) ([]*pb.Service, error) {
 }
 
 func metricsURL(o config.Options) (*url.URL, error) {
+	host, port, err := net.SplitHostPort(o.MetricsAddr)
+	if err != nil {
+		return nil, fmt.Errorf("invalid metrics address %q: %w", o.MetricsAddr, err)
+	}
+	if port == "" {
+		return nil, fmt.Errorf("invalid metrics value %q: port is required", o.MetricsAddr)
+	}
+	if host == "" {
+		if host, err = getHostOrIP(); err != nil {
+			return nil, fmt.Errorf("could not guess hostname: %w", err)
+		}
+	}
+
 	u := url.URL{
 		Scheme: "http",
-		Host:   o.MetricsAddr,
+		Host:   net.JoinHostPort(host, port),
 		Path:   defaultMetricsPath,
 	}
 
@@ -107,19 +120,6 @@ func metricsURL(o config.Options) (*url.URL, error) {
 		return nil, fmt.Errorf("no metrics address provided")
 	}
 
-	host, port, err := net.SplitHostPort(o.MetricsAddr)
-	if err != nil {
-		return nil, fmt.Errorf("invalid metrics address %q: %w", o.MetricsAddr, err)
-	}
-
-	if port == "" {
-		return nil, fmt.Errorf("invalid metrics value %q: port is required", o.MetricsAddr)
-	}
-
-	if host == "" {
-		return nil, fmt.Errorf("invalid metrics value %q: either host or IP address is required", o.MetricsAddr)
-	}
-
 	return &u, nil
 }
 

internal/registry/reporter_test.go

@@ -24,7 +24,6 @@ func TestMetricsURL(t *testing.T) {
 	for _, opt := range []config.Options{
 		{MetricsAddr: "my.host:"},
 		{MetricsAddr: "my.host:9090", MetricsBasicAuth: "SMTH"},
-		{MetricsAddr: ":9090"},
 		{MetricsAddr: "my.host"},
 	} {
 		_, err := metricsURL(opt)