Enhance DNS failover reliability (netbirdio#1637)

* Fix using wrong array index in log to avoid potential panic

* Increase gRPC connection timeout and add the timeout resolv.conf option

This makes sure the dns client is able to failover to a second
configured nameserver, if present. That is the case then when using the
dns `file` manager and a resolv.conf file generated for netbird.

* On file backup restore, remove the first NS if it's the netbird NS

* Bump dns mangager discovery message from debug to info to ease debugging

client/internal/dns/file_linux.go

@@ -8,6 +8,7 @@ import (
 	"net/netip"
 	"os"
 	"strings"
+	"time"
 
 	log "github.com/sirupsen/logrus"
 )
@@ -23,10 +24,16 @@ const (
 	fileMaxNumberOfSearchDomains = 6
 )
 
+const (
+	dnsFailoverTimeout  = 4 * time.Second
+	dnsFailoverAttempts = 1
+)
+
 type fileConfigurator struct {
 	repair *repair
 
-	originalPerms os.FileMode
+	originalPerms  os.FileMode
+	nbNameserverIP string
 }
 
 func newFileConfigurator() (hostManager, error) {
@@ -64,7 +71,7 @@ func (f *fileConfigurator) applyDNSConfig(config HostDNSConfig) error {
 	}
 
 	nbSearchDomains := searchDomains(config)
-	nbNameserverIP := config.ServerIP
+	f.nbNameserverIP = config.ServerIP
 
 	resolvConf, err := parseBackupResolvConf()
 	if err != nil {
@@ -73,22 +80,23 @@ func (f *fileConfigurator) applyDNSConfig(config HostDNSConfig) error {
 
 	f.repair.stopWatchFileChanges()
 
-	err = f.updateConfig(nbSearchDomains, nbNameserverIP, resolvConf)
+	err = f.updateConfig(nbSearchDomains, f.nbNameserverIP, resolvConf)
 	if err != nil {
 		return err
 	}
-	f.repair.watchFileChanges(nbSearchDomains, nbNameserverIP)
+	f.repair.watchFileChanges(nbSearchDomains, f.nbNameserverIP)
 	return nil
 }
 
 func (f *fileConfigurator) updateConfig(nbSearchDomains []string, nbNameserverIP string, cfg *resolvConf) error {
 	searchDomainList := mergeSearchDomains(nbSearchDomains, cfg.searchDomains)
 	nameServers := generateNsList(nbNameserverIP, cfg)
 
+	options := prepareOptionsWithTimeout(cfg.others, int(dnsFailoverTimeout.Seconds()), dnsFailoverAttempts)
 	buf := prepareResolvConfContent(
 		searchDomainList,
 		nameServers,
-		cfg.others)
+		options)
 
 	log.Debugf("creating managed file %s", defaultResolvConfPath)
 	err := os.WriteFile(defaultResolvConfPath, buf.Bytes(), f.originalPerms)
@@ -131,7 +139,12 @@ func (f *fileConfigurator) backup() error {
 }
 
 func (f *fileConfigurator) restore() error {
-	err := copyFile(fileDefaultResolvConfBackupLocation, defaultResolvConfPath)
+	err := removeFirstNbNameserver(fileDefaultResolvConfBackupLocation, f.nbNameserverIP)
+	if err != nil {
+		log.Errorf("Failed to remove netbird nameserver from %s on backup restore: %s", fileDefaultResolvConfBackupLocation, err)
+	}
+
+	err = copyFile(fileDefaultResolvConfBackupLocation, defaultResolvConfPath)
 	if err != nil {
 		return fmt.Errorf("restoring %s from %s: %w", defaultResolvConfPath, fileDefaultResolvConfBackupLocation, err)
 	}
@@ -157,7 +170,7 @@ func (f *fileConfigurator) restoreUncleanShutdownDNS(storedDNSAddress *netip.Add
 	currentDNSAddress, err := netip.ParseAddr(resolvConf.nameServers[0])
 	// not a valid first nameserver -> restore
 	if err != nil {
-		log.Errorf("restoring unclean shutdown: parse dns address %s failed: %s", resolvConf.nameServers[1], err)
+		log.Errorf("restoring unclean shutdown: parse dns address %s failed: %s", resolvConf.nameServers[0], err)
 		return restoreResolvConfFile()
 	}
 

client/internal/dns/file_parser_linux.go

@@ -5,6 +5,7 @@ package dns
 import (
 	"fmt"
 	"os"
+	"regexp"
 	"strings"
 
 	log "github.com/sirupsen/logrus"
@@ -14,6 +15,9 @@ const (
 	defaultResolvConfPath = "/etc/resolv.conf"
 )
 
+var timeoutRegex = regexp.MustCompile(`timeout:\d+`)
+var attemptsRegex = regexp.MustCompile(`attempts:\d+`)
+
 type resolvConf struct {
 	nameServers   []string
 	searchDomains []string
@@ -103,3 +107,62 @@ func parseResolvConfFile(resolvConfFile string) (*resolvConf, error) {
 	}
 	return rconf, nil
 }
+
+// prepareOptionsWithTimeout appends timeout to existing options if it doesn't exist,
+// otherwise it adds a new option with timeout and attempts.
+func prepareOptionsWithTimeout(input []string, timeout int, attempts int) []string {
+	configs := make([]string, len(input))
+	copy(configs, input)
+
+	for i, config := range configs {
+		if strings.HasPrefix(config, "options") {
+			config = strings.ReplaceAll(config, "rotate", "")
+			config = strings.Join(strings.Fields(config), " ")
+
+			if strings.Contains(config, "timeout:") {
+				config = timeoutRegex.ReplaceAllString(config, fmt.Sprintf("timeout:%d", timeout))
+			} else {
+				config = strings.Replace(config, "options ", fmt.Sprintf("options timeout:%d ", timeout), 1)
+			}
+
+			if strings.Contains(config, "attempts:") {
+				config = attemptsRegex.ReplaceAllString(config, fmt.Sprintf("attempts:%d", attempts))
+			} else {
+				config = strings.Replace(config, "options ", fmt.Sprintf("options attempts:%d ", attempts), 1)
+			}
+
+			configs[i] = config
+			return configs
+		}
+	}
+
+	return append(configs, fmt.Sprintf("options timeout:%d attempts:%d", timeout, attempts))
+}
+
+// removeFirstNbNameserver removes the given nameserver from the given file if it is in the first position
+// and writes the file back to the original location
+func removeFirstNbNameserver(filename, nameserverIP string) error {
+	resolvConf, err := parseResolvConfFile(filename)
+	if err != nil {
+		return fmt.Errorf("parse backup resolv.conf: %w", err)
+	}
+	content, err := os.ReadFile(filename)
+	if err != nil {
+		return fmt.Errorf("read %s: %w", filename, err)
+	}
+
+	if len(resolvConf.nameServers) > 1 && resolvConf.nameServers[0] == nameserverIP {
+		newContent := strings.Replace(string(content), fmt.Sprintf("nameserver %s\n", nameserverIP), "", 1)
+
+		stat, err := os.Stat(filename)
+		if err != nil {
+			return fmt.Errorf("stat %s: %w", filename, err)
+		}
+		if err := os.WriteFile(filename, []byte(newContent), stat.Mode()); err != nil {
+			return fmt.Errorf("write %s: %w", filename, err)
+		}
+
+	}
+
+	return nil
+}

client/internal/dns/file_parser_linux_test.go

@@ -6,6 +6,8 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func Test_parseResolvConf(t *testing.T) {
@@ -172,3 +174,131 @@ nameserver 192.168.0.1
 		t.Errorf("unexpected resolv.conf content: %v", cfg)
 	}
 }
+
+func TestPrepareOptionsWithTimeout(t *testing.T) {
+	tests := []struct {
+		name     string
+		others   []string
+		timeout  int
+		attempts int
+		expected []string
+	}{
+		{
+			name:     "Append new options with timeout and attempts",
+			others:   []string{"some config"},
+			timeout:  2,
+			attempts: 2,
+			expected: []string{"some config", "options timeout:2 attempts:2"},
+		},
+		{
+			name:     "Modify existing options to exclude rotate and include timeout and attempts",
+			others:   []string{"some config", "options rotate someother"},
+			timeout:  3,
+			attempts: 2,
+			expected: []string{"some config", "options attempts:2 timeout:3 someother"},
+		},
+		{
+			name:     "Existing options with timeout and attempts are updated",
+			others:   []string{"some config", "options timeout:4 attempts:3"},
+			timeout:  5,
+			attempts: 4,
+			expected: []string{"some config", "options timeout:5 attempts:4"},
+		},
+		{
+			name:     "Modify existing options, add missing attempts before timeout",
+			others:   []string{"some config", "options timeout:4"},
+			timeout:  4,
+			attempts: 3,
+			expected: []string{"some config", "options attempts:3 timeout:4"},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := prepareOptionsWithTimeout(tc.others, tc.timeout, tc.attempts)
+			assert.Equal(t, tc.expected, result)
+		})
+	}
+}
+
+func TestRemoveFirstNbNameserver(t *testing.T) {
+	testCases := []struct {
+		name       string
+		content    string
+		ipToRemove string
+		expected   string
+	}{
+		{
+			name: "Unrelated nameservers with comments and options",
+			content: `# This is a comment
+options rotate
+nameserver 1.1.1.1
+# Another comment
+nameserver 8.8.4.4
+search example.com`,
+			ipToRemove: "9.9.9.9",
+			expected: `# This is a comment
+options rotate
+nameserver 1.1.1.1
+# Another comment
+nameserver 8.8.4.4
+search example.com`,
+		},
+		{
+			name: "First nameserver matches",
+			content: `search example.com
+nameserver 9.9.9.9
+# oof, a comment
+nameserver 8.8.4.4
+options attempts:5`,
+			ipToRemove: "9.9.9.9",
+			expected: `search example.com
+# oof, a comment
+nameserver 8.8.4.4
+options attempts:5`,
+		},
+		{
+			name: "Target IP not the first nameserver",
+			// nolint:dupword
+			content: `# Comment about the first nameserver
+nameserver 8.8.4.4
+# Comment before our target
+nameserver 9.9.9.9
+options timeout:2`,
+			ipToRemove: "9.9.9.9",
+			// nolint:dupword
+			expected: `# Comment about the first nameserver
+nameserver 8.8.4.4
+# Comment before our target
+nameserver 9.9.9.9
+options timeout:2`,
+		},
+		{
+			name: "Only nameserver matches",
+			content: `options debug
+nameserver 9.9.9.9
+search localdomain`,
+			ipToRemove: "9.9.9.9",
+			expected: `options debug
+nameserver 9.9.9.9
+search localdomain`,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			tempDir := t.TempDir()
+			tempFile := filepath.Join(tempDir, "resolv.conf")
+			err := os.WriteFile(tempFile, []byte(tc.content), 0644)
+			assert.NoError(t, err)
+
+			err = removeFirstNbNameserver(tempFile, tc.ipToRemove)
+			assert.NoError(t, err)
+
+			content, err := os.ReadFile(tempFile)
+			assert.NoError(t, err)
+
+			assert.Equal(t, tc.expected, string(content), "The resulting content should match the expected output.")
+		})
+	}
+}

client/internal/dns/host_linux.go

@@ -65,7 +65,7 @@ func newHostManager(wgInterface string) (hostManager, error) {
 		return nil, err
 	}
 
-	log.Debugf("discovered mode is: %s", osManager)
+	log.Infof("System DNS manager discovered: %s", osManager)
 	return newHostManagerFromType(wgInterface, osManager)
 }
 

client/internal/dns/resolvconf_linux.go

@@ -53,10 +53,12 @@ func (r *resolvconf) applyDNSConfig(config HostDNSConfig) error {
 	searchDomainList := searchDomains(config)
 	searchDomainList = mergeSearchDomains(searchDomainList, r.originalSearchDomains)
 
+	options := prepareOptionsWithTimeout(r.othersConfigs, int(dnsFailoverTimeout.Seconds()), dnsFailoverAttempts)
+
 	buf := prepareResolvConfContent(
 		searchDomainList,
 		append([]string{config.ServerIP}, r.originalNameServers...),
-		r.othersConfigs)
+		options)
 
 	// create a backup for unclean shutdown detection before the resolv.conf is changed
 	if err := createUncleanShutdownIndicator(defaultResolvConfPath, resolvConfManager, config.ServerIP); err != nil {

management/client/grpc.go

@@ -26,6 +26,8 @@ import (
 	"github.com/netbirdio/netbird/management/proto"
 )
 
+const ConnectTimeout = 10 * time.Second
+
 // ConnStateNotifier is a wrapper interface of the status recorders
 type ConnStateNotifier interface {
 	MarkManagementDisconnected(error)
@@ -49,7 +51,7 @@ func NewClient(ctx context.Context, addr string, ourPrivateKey wgtypes.Key, tlsE
 		transportOption = grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{}))
 	}
 
-	mgmCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	mgmCtx, cancel := context.WithTimeout(ctx, ConnectTimeout)
 	defer cancel()
 	conn, err := grpc.DialContext(
 		mgmCtx,
@@ -318,7 +320,7 @@ func (c *GrpcClient) login(serverKey wgtypes.Key, req *proto.LoginRequest) (*pro
 		log.Errorf("failed to encrypt message: %s", err)
 		return nil, err
 	}
-	mgmCtx, cancel := context.WithTimeout(c.ctx, 5*time.Second)
+	mgmCtx, cancel := context.WithTimeout(c.ctx, ConnectTimeout)
 	defer cancel()
 	resp, err := c.realClient.Login(mgmCtx, &proto.EncryptedMessage{
 		WgPubKey: c.key.PublicKey().String(),

signal/client/grpc.go

@@ -21,11 +21,10 @@ import (
 	"google.golang.org/grpc/status"
 
 	"github.com/netbirdio/netbird/encryption"
+	"github.com/netbirdio/netbird/management/client"
 	"github.com/netbirdio/netbird/signal/proto"
 )
 
-const defaultSendTimeout = 5 * time.Second
-
 // ConnStateNotifier is a wrapper interface of the status recorder
 type ConnStateNotifier interface {
 	MarkSignalDisconnected(error)
@@ -71,7 +70,7 @@ func NewClient(ctx context.Context, addr string, key wgtypes.Key, tlsEnabled boo
 		transportOption = grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{}))
 	}
 
-	sigCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	sigCtx, cancel := context.WithTimeout(ctx, client.ConnectTimeout)
 	defer cancel()
 	conn, err := grpc.DialContext(
 		sigCtx,
@@ -353,7 +352,7 @@ func (c *GrpcClient) Send(msg *proto.Message) error {
 		return err
 	}
 
-	attemptTimeout := defaultSendTimeout
+	attemptTimeout := client.ConnectTimeout
 
 	for attempt := 0; attempt < 4; attempt++ {
 		if attempt > 1 {