Add support for hostnames in addresses

Signed-off-by: Knut Ahlers <knut@ahlers.me>

pkg/iptables/iptables.go

@@ -4,6 +4,7 @@ package iptables
 
 import (
 	"fmt"
+	"net"
 	"regexp"
 	"strconv"
 	"strings"
@@ -11,6 +12,7 @@ import (
 
 	coreosIptables "github.com/coreos/go-iptables/iptables"
 	"github.com/mitchellh/hashstructure/v2"
+	"github.com/sirupsen/logrus"
 )
 
 const (
@@ -175,6 +177,26 @@ func (c *Client) buildServiceTable(service string, cType chainType) (rules [][]s
 	}
 
 	for _, nt := range c.services[service] {
+		var (
+			bindAddr, localAddr, targetAddr string
+			err                             error
+		)
+
+		if bindAddr, err = c.translateToIP(nt.BindAddr); err != nil {
+			logrus.WithError(err).WithField("bind_addr", nt.BindAddr).Error("invalid address")
+			continue
+		}
+
+		if targetAddr, err = c.translateToIP(nt.Addr); err != nil {
+			logrus.WithError(err).WithField("target_addr", nt.Addr).Error("invalid address")
+			continue
+		}
+
+		if localAddr, err = c.translateToIP(nt.LocalAddr); err != nil {
+			logrus.WithError(err).WithField("local_addr", nt.LocalAddr).Error("invalid address")
+			continue
+		}
+
 		switch cType {
 		case chainTypeDNAT:
 			rules = append(rules, []string{
@@ -183,21 +205,21 @@ func (c *Client) buildServiceTable(service string, cType chainType) (rules [][]s
 				"--probability", strconv.FormatFloat(nt.Weight/weightLeft, 'f', probPrecision, probBitsize),
 
 				"-p", nt.Proto,
-				"-d", nt.BindAddr,
+				"-d", bindAddr,
 				"--dport", strconv.Itoa(nt.BindPort),
 
 				"-j", "DNAT",
-				"--to-destination", fmt.Sprintf("%s:%d", nt.Addr, nt.Port),
+				"--to-destination", fmt.Sprintf("%s:%d", targetAddr, nt.Port),
 			})
 
 		case chainTypeSNAT:
 			rules = append(rules, []string{
 				"-p", nt.Proto,
-				"-d", nt.Addr,
+				"-d", targetAddr,
 				"--dport", strconv.Itoa(nt.Port),
 
 				"-j", "SNAT",
-				"--to-source", nt.LocalAddr,
+				"--to-source", localAddr,
 			})
 		}
 
@@ -243,6 +265,29 @@ func (*Client) tableName(components ...string) string {
 	return strings.Join(parts, "_")
 }
 
+func (*Client) translateToIP(addr string) (string, error) {
+	ip := net.ParseIP(addr)
+	if ip != nil {
+		// We got either valid IPv4 or IPv6: Just return that.
+		return ip.String(), nil
+	}
+
+	// Was no IP, might be a hostname: Look it up
+	ips, err := net.LookupIP(addr)
+	if err != nil {
+		// Definitely was none.
+		return "", fmt.Errorf("resolving %q to ip: %w", addr, err)
+	}
+
+	if len(ips) == 0 {
+		// Maybe was one but had no addresses.
+		return "", fmt.Errorf("resolving %q did not yield IPs", addr)
+	}
+
+	// Had one or more addresses, we take the first one
+	return ips[0].String(), nil
+}
+
 func (n NATTarget) equals(c NATTarget) bool {
 	nh, _ := hashstructure.Hash(n, hashstructure.FormatV2, nil)
 	ch, _ := hashstructure.Hash(c, hashstructure.FormatV2, nil)