fix: automatically detect dns lookup family for cp cluster

pkg/xds/bootstrap/template_v3.go

@@ -1,6 +1,7 @@
 package bootstrap
 
 import (
+	"net"
 	"strconv"
 
 	"github.com/asaskevich/govalidator"
@@ -171,6 +172,7 @@ func genConfig(parameters configParameters) (*envoy_bootstrap_v3.Bootstrap, erro
 						},
 					},
 					ClusterDiscoveryType: &envoy_cluster_v3.Cluster_Type{Type: clusterTypeFromHost(parameters.XdsHost)},
+					DnsLookupFamily:      dnsLookupFamilyFromXdsHost(parameters.XdsHost, net.LookupIP),
 					LoadAssignment: &envoy_config_endpoint_v3.ClusterLoadAssignment{
 						ClusterName: "ads_cluster",
 						Endpoints: []*envoy_config_endpoint_v3.LocalityLbEndpoints{
@@ -295,6 +297,29 @@ func genConfig(parameters configParameters) (*envoy_bootstrap_v3.Bootstrap, erro
 	return res, nil
 }
 
+func dnsLookupFamilyFromXdsHost(host string, lookupFn func(host string) ([]net.IP, error)) envoy_cluster_v3.Cluster_DnsLookupFamily {
+	if govalidator.IsDNSName(host) && host != "localhost" {
+		ips, err := lookupFn(host)
+		if err != nil {
+			log.Info("[WARNING] error looking up XDS host to determine DnsLookupFamily, falling back to AUTO", "hostname", host)
+			return envoy_cluster_v3.Cluster_AUTO
+		}
+		hasIPv6 := false
+
+		for _, ip := range ips {
+			if ip.To4() == nil {
+				hasIPv6 = true
+			}
+		}
+
+		if !hasIPv6 && len(ips) > 0 {
+			return envoy_cluster_v3.Cluster_V4_ONLY
+		}
+	}
+
+	return envoy_cluster_v3.Cluster_AUTO // default
+}
+
 func clusterTypeFromHost(host string) envoy_cluster_v3.Cluster_DiscoveryType {
 	if govalidator.IsIP(host) {
 		return envoy_cluster_v3.Cluster_STATIC

pkg/xds/bootstrap/template_v3_test.go

@@ -0,0 +1,90 @@
+package bootstrap
+
+import (
+	"errors"
+	"net"
+
+	envoy_cluster_v3 "github.com/envoyproxy/go-control-plane/envoy/config/cluster/v3"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("dnsLookupFamilyFromXdsHost", func() {
+	It("should return AUTO when IPv6 found", func() {
+		// given
+		lookupFn := func(host string) ([]net.IP, error) {
+			return []net.IP{net.IPv6loopback}, nil
+		}
+
+		// when
+		result := dnsLookupFamilyFromXdsHost("example.com", lookupFn)
+
+		// then
+		Expect(result).To(Equal(envoy_cluster_v3.Cluster_AUTO))
+	})
+
+	It("should return AUTO for localhost", func() {
+		// given
+		lookupFn := func(host string) ([]net.IP, error) {
+			return []net.IP{net.IPv4(127, 0, 0, 1)}, nil
+		}
+
+		// when
+		result := dnsLookupFamilyFromXdsHost("localhost", lookupFn)
+
+		// then
+		Expect(result).To(Equal(envoy_cluster_v3.Cluster_AUTO))
+	})
+
+	It("should return AUTO when both IPv6 and IPv4 found", func() {
+		// given
+		lookupFn := func(host string) ([]net.IP, error) {
+			return []net.IP{net.IPv6loopback, net.IPv4(127, 0, 0, 1)}, nil
+		}
+
+		// when
+		result := dnsLookupFamilyFromXdsHost("example.com", lookupFn)
+
+		// then
+		Expect(result).To(Equal(envoy_cluster_v3.Cluster_AUTO))
+	})
+
+	It("should return IPV4 when only IPv4 found", func() {
+		// given
+		lookupFn := func(host string) ([]net.IP, error) {
+			return []net.IP{net.IPv4(127, 0, 0, 1)}, nil
+		}
+
+		// when
+		result := dnsLookupFamilyFromXdsHost("example.com", lookupFn)
+
+		// then
+		Expect(result).To(Equal(envoy_cluster_v3.Cluster_V4_ONLY))
+	})
+
+	It("should return AUTO (default) when no ips returned", func() {
+		// given
+		lookupFn := func(host string) ([]net.IP, error) {
+			return []net.IP{}, nil
+		}
+
+		// when
+		result := dnsLookupFamilyFromXdsHost("example.com", lookupFn)
+
+		// then
+		Expect(result).To(Equal(envoy_cluster_v3.Cluster_AUTO))
+	})
+
+	It("should return AUTO when error occurs", func() {
+		// given
+		lookupFn := func(host string) ([]net.IP, error) {
+			return nil, errors.New("could not resolve hostname")
+		}
+
+		// when
+		result := dnsLookupFamilyFromXdsHost("example.com", lookupFn)
+
+		// then
+		Expect(result).To(Equal(envoy_cluster_v3.Cluster_AUTO))
+	})
+})