feat(localdns): auto-detect local DNS resolvers

- Local DNS resolvers default to system DNS servers if not set
- Local DNS middleware enabled by default
- Add environment variable `MIDDLEWARE_LOCALDNS_ENABLED=on`

Dockerfile

@@ -81,6 +81,7 @@ ENV \
     MIDDLEWARE_LOG_DIRECTORY=/var/log/dns/ \
     MIDDLEWARE_LOG_REQUESTS=on \
     MIDDLEWARE_LOG_RESPONSES=off \
+    MIDDLEWARE_LOCALDNS_ENABLED=on \
     MIDDLEWARE_LOCALDNS_RESOLVERS= \
     CACHE_TYPE=lru \
     CACHE_LRU_MAX_ENTRIES=10000 \

README.md

@@ -141,7 +141,8 @@ If you're running Kubernetes, there is a separate article on [how to set up K8s]
 | `METRICS_TYPE` | `noop` | `noop` or `prometheus` |
 | `METRICS_PROMETHEUS_ADDRESS` | `:9090` | HTTP Prometheus server listening address |
 | `METRICS_PROMETHEUS_SUBSYSTEM` | `dns` | Prometheus metrics prefix/subsystem |
-| `MIDDLEWARE_LOCALDNS_RESOLVERS` | | Comma separated list of local DNS resolvers to use for local names DNS requests |
+| `MIDDLEWARE_LOCALDNS_ENABLED` | `on` | Enable or disable the local DNS middleware |
+| `MIDDLEWARE_LOCALDNS_RESOLVERS` | Local DNS servers | Comma separated list of local DNS resolvers to use for local names DNS requests |
 | `CHECK_DNS` | `on` | `on` or `off`. Check resolving github.com using `127.0.0.1:53` at start |
 | `UPDATE_PERIOD` | `24h` | Period to update block lists and restart Unbound. Set to `0` to disable. |
 

internal/config/localdns.go

@@ -5,11 +5,14 @@ import (
 	"fmt"
 	"net/netip"
 
+	"github.com/qdm12/dns/v2/pkg/nameserver"
+	"github.com/qdm12/gosettings"
 	"github.com/qdm12/gosettings/reader"
 	"github.com/qdm12/gotree"
 )
 
 type LocalDNS struct {
+	Enabled   *bool
 	Resolvers []netip.AddrPort
 }
 
@@ -18,6 +21,12 @@ var (
 	ErrLocalResolverPortIsZero      = errors.New("local resolver port is zero")
 )
 
+func (l *LocalDNS) setDefault() {
+	l.Enabled = gosettings.DefaultPointer(l.Enabled, true)
+	l.Resolvers = gosettings.DefaultSlice(l.Resolvers,
+		nameserver.GetDNSServers())
+}
+
 func (l *LocalDNS) validate() (err error) {
 	for _, resolver := range l.Resolvers {
 		switch {
@@ -38,7 +47,7 @@ func (l *LocalDNS) String() string {
 }
 
 func (l *LocalDNS) ToLinesNode() (node *gotree.Node) {
-	if len(l.Resolvers) == 0 {
+	if !*l.Enabled {
 		return gotree.New("Local DNS middleware: disabled")
 	}
 
@@ -52,6 +61,11 @@ func (l *LocalDNS) ToLinesNode() (node *gotree.Node) {
 }
 
 func (l *LocalDNS) read(reader *reader.Reader) (err error) {
+	l.Enabled, err = reader.BoolPtr("MIDDLEWARE_LOCALDNS_ENABLED")
+	if err != nil {
+		return err
+	}
+
 	l.Resolvers, err = reader.CSVNetipAddrPorts("MIDDLEWARE_LOCALDNS_RESOLVERS")
 	if err != nil {
 		return err

internal/config/settings.go

@@ -46,6 +46,7 @@ func (s *Settings) SetDefaults() {
 	s.Log.setDefaults()
 	s.MiddlewareLog.setDefaults()
 	s.Metrics.setDefaults()
+	s.LocalDNS.setDefault()
 	s.CheckDNS = gosettings.DefaultPointer(s.CheckDNS, true)
 	const defaultUpdaterPeriod = 24 * time.Hour
 	s.UpdatePeriod = gosettings.DefaultPointer(s.UpdatePeriod, defaultUpdaterPeriod)

internal/setup/dns.go

@@ -61,9 +61,9 @@ func setupMiddlewares(userSettings config.Settings, cache Cache,
 	}
 	middlewares = append(middlewares, cacheMiddleware)
 
-	if len(userSettings.LocalDNS.Resolvers) > 0 {
+	if *userSettings.LocalDNS.Enabled {
 		localDNSMiddleware, err := localdns.New(localdns.Settings{
-			Resolvers: userSettings.LocalDNS.Resolvers,
+			Resolvers: userSettings.LocalDNS.Resolvers, // possibly auto-detected
 			Logger:    logger,
 		})
 		if err != nil {

pkg/middlewares/localdns/settings.go

@@ -6,6 +6,7 @@ import (
 	"net/netip"
 
 	"github.com/qdm12/dns/v2/pkg/log/noop"
+	"github.com/qdm12/dns/v2/pkg/nameserver"
 	"github.com/qdm12/gosettings"
 	"github.com/qdm12/gotree"
 )
@@ -14,14 +15,15 @@ type Settings struct {
 	// Resolvers is the list of resolvers to use to resolve the
 	// local domain names. They are each tried after the other
 	// in order, until one returns an answer for the question.
-	// This field must be set and non empty.
+	// If left empty, the local nameservers found are used.
 	Resolvers []netip.AddrPort
 	// Logger is the logger to use.
 	// It defaults to a No-op implementation.
 	Logger Logger
 }
 
 func (s *Settings) SetDefaults() {
+	s.Resolvers = gosettings.DefaultSlice(s.Resolvers, nameserver.GetDNSServers())
 	s.Logger = gosettings.DefaultComparable[Logger](s.Logger, noop.New())
 }