fix: pass IPv6 DNS resolvers correctly

internal/controller/nginx/config/base_http_config.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"fmt"
+	"net"
 	gotemplate "text/template"
 
 	"github.com/nginx/nginx-gateway-fabric/v2/internal/controller/nginx/config/shared"
@@ -34,7 +36,7 @@ func executeBaseHTTPConfig(conf dataplane.Configuration) []executeResult {
 		Includes:                includes,
 		NginxReadinessProbePort: conf.BaseHTTPConfig.NginxReadinessProbePort,
 		IPFamily:                getIPFamily(conf.BaseHTTPConfig),
-		DNSResolver:             conf.BaseHTTPConfig.DNSResolver,
+		DNSResolver:             buildDNSResolver(conf.BaseHTTPConfig.DNSResolver),
 		AccessLog:               buildAccessLog(conf.Logging.AccessLog),
 		GatewaySecretID:         conf.BaseHTTPConfig.GatewaySecretID,
 	}
@@ -49,6 +51,34 @@ func executeBaseHTTPConfig(conf dataplane.Configuration) []executeResult {
 	return results
 }
 
+func buildDNSResolver(dnsResolver *dataplane.DNSResolverConfig) *dataplane.DNSResolverConfig {
+	if dnsResolver == nil {
+		return nil
+	}
+
+	fixed := &dataplane.DNSResolverConfig{
+		Timeout:     dnsResolver.Timeout,
+		Valid:       dnsResolver.Valid,
+		DisableIPv6: dnsResolver.DisableIPv6,
+	}
+
+	for _, address := range dnsResolver.Addresses {
+		ip := net.ParseIP(address)
+		if ip == nil {
+			continue
+		}
+
+		if ip.To4() == nil {
+			// nginx expects IPv6 DNS resolvers to be passed with brackets
+			fixed.Addresses = append(fixed.Addresses, fmt.Sprintf("[%s]", address))
+		} else {
+			fixed.Addresses = append(fixed.Addresses, address)
+		}
+	}
+
+	return fixed
+}
+
 func buildAccessLog(accessLogConfig *dataplane.AccessLog) *AccessLog {
 	if accessLogConfig != nil {
 		accessLog := &AccessLog{

internal/controller/nginx/config/base_http_config_test.go

@@ -317,6 +317,28 @@ func TestExecuteBaseHttp_DNSResolver(t *testing.T) {
 			},
 			expectedConfig: "resolver 8.8.8.8;",
 		},
+		{
+			name: "DNS resolver with single IPv6 address",
+			conf: dataplane.Configuration{
+				BaseHTTPConfig: dataplane.BaseHTTPConfig{
+					DNSResolver: &dataplane.DNSResolverConfig{
+						Addresses: []string{"2606:4700:4700::64"},
+					},
+				},
+			},
+			expectedConfig: "resolver [2606:4700:4700::64];",
+		},
+		{
+			name: "DNS resolver with one IPv6 address and one IPv4 address",
+			conf: dataplane.Configuration{
+				BaseHTTPConfig: dataplane.BaseHTTPConfig{
+					DNSResolver: &dataplane.DNSResolverConfig{
+						Addresses: []string{"2606:4700:4700::64", "8.8.8.8"},
+					},
+				},
+			},
+			expectedConfig: "resolver [2606:4700:4700::64] 8.8.8.8;",
+		},
 		{
 			name: "no DNS resolver",
 			conf: dataplane.Configuration{

internal/controller/nginx/config/stream_servers.go

@@ -19,7 +19,7 @@ func (g GeneratorImpl) executeStreamServers(conf dataplane.Configuration) []exec
 		Servers:     streamServers,
 		IPFamily:    getIPFamily(conf.BaseHTTPConfig),
 		Plus:        g.plus,
-		DNSResolver: conf.BaseStreamConfig.DNSResolver,
+		DNSResolver: buildDNSResolver(conf.BaseStreamConfig.DNSResolver),
 	}
 
 	streamServerResult := executeResult{

internal/controller/nginx/config/stream_servers_test.go

@@ -471,7 +471,7 @@ server {
 			},
 			expectedConfig: `
 # DNS resolver configuration for ExternalName services
-resolver 2001:4860:4860::8888 valid=30s;
+resolver [2001:4860:4860::8888] valid=30s;
 resolver_timeout 5s;
 
 server {