Add support for NextDNS resolver

CHANGELOG.md

@@ -27,6 +27,7 @@
 - Fix some DNS config issues [#660](https://github.com/juanfont/headscale/issues/660)
 - Make it possible to disable TS2019 with build flag [#928](https://github.com/juanfont/headscale/pull/928)
 - Fix OIDC registration issues [#960](https://github.com/juanfont/headscale/pull/960) and [#971](https://github.com/juanfont/headscale/pull/971)
+- Add support for specifying NextDNS DNS-over-HTTPS resolver [#940](https://github.com/juanfont/headscale/pull/940)
 
 ## 0.16.4 (2022-08-21)
 

config-example.yaml

@@ -214,6 +214,18 @@ dns_config:
   nameservers:
     - 1.1.1.1
 
+  # NextDNS (see https://tailscale.com/kb/1218/nextdns/).
+  # "abc123" is example NextDNS ID, replace with yours.
+  #
+  # With metadata sharing:
+  # nameservers:
+  #   - https://dns.nextdns.io/abc123
+  #
+  # Without metadata sharing:
+  # nameservers:
+  #   - 2a07:a8c0::ab:c123
+  #   - 2a07:a8c1::ab:c123
+
   # Split DNS (see https://tailscale.com/kb/1054/dns/),
   # list of search domains and the DNS to query for each one.
   #

config.go

@@ -383,10 +383,21 @@ func GetDNSConfig() (*tailcfg.DNSConfig, string) {
 		if viper.IsSet("dns_config.nameservers") {
 			nameserversStr := viper.GetStringSlice("dns_config.nameservers")
 
-			nameservers := make([]netip.Addr, len(nameserversStr))
-			resolvers := make([]*dnstype.Resolver, len(nameserversStr))
+			nameservers := []netip.Addr{}
+			resolvers := []*dnstype.Resolver{}
 
-			for index, nameserverStr := range nameserversStr {
+			for _, nameserverStr := range nameserversStr {
+				// Search for explicit DNS-over-HTTPS resolvers
+				if strings.HasPrefix(nameserverStr, "https://") {
+					resolvers = append(resolvers, &dnstype.Resolver{
+						Addr: nameserverStr,
+					})
+
+					// This nameserver can not be parsed as an IP address
+					continue
+				}
+
+				// Parse nameserver as a regular IP
 				nameserver, err := netip.ParseAddr(nameserverStr)
 				if err != nil {
 					log.Error().
@@ -395,10 +406,10 @@ func GetDNSConfig() (*tailcfg.DNSConfig, string) {
 						Msgf("Could not parse nameserver IP: %s", nameserverStr)
 				}
 
-				nameservers[index] = nameserver
-				resolvers[index] = &dnstype.Resolver{
+				nameservers = append(nameservers, nameserver)
+				resolvers = append(resolvers, &dnstype.Resolver{
 					Addr: nameserver.String(),
-				}
+				})
 			}
 
 			dnsConfig.Nameservers = nameservers

dns.go

@@ -3,11 +3,13 @@ package headscale
 import (
 	"fmt"
 	"net/netip"
+	"net/url"
 	"strings"
 
 	mapset "github.com/deckarep/golang-set/v2"
 	"go4.org/netipx"
 	"tailscale.com/tailcfg"
+	"tailscale.com/types/dnstype"
 	"tailscale.com/util/dnsname"
 )
 
@@ -20,6 +22,10 @@ const (
 	ipv6AddressLength = 128
 )
 
+const (
+	nextDNSDoHPrefix = "https://dns.nextdns.io"
+)
+
 // generateMagicDNSRootDomains generates a list of DNS entries to be included in `Routes` in `MapResponse`.
 // This list of reverse DNS entries instructs the OS on what subnets and domains the Tailscale embedded DNS
 // server (listening in 100.100.100.100 udp/53) should be used for.
@@ -152,16 +158,39 @@ func generateIPv6DNSRootDomain(ipPrefix netip.Prefix) []dnsname.FQDN {
 	return fqdns
 }
 
+// If any nextdns DoH resolvers are present in the list of resolvers it will
+// take metadata from the machine metadata and instruct tailscale to add it
+// to the requests. This makes it possible to identify from which device the
+// requests come in the NextDNS dashboard.
+//
+// This will produce a resolver like:
+// `https://dns.nextdns.io/<nextdns-id>?device_name=node-name&device_model=linux&device_ip=100.64.0.1`
+func addNextDNSMetadata(resolvers []*dnstype.Resolver, machine Machine) {
+	for _, resolver := range resolvers {
+		if strings.HasPrefix(resolver.Addr, nextDNSDoHPrefix) {
+			attrs := url.Values{
+				"device_name":  []string{machine.Hostname},
+				"device_model": []string{machine.HostInfo.OS},
+			}
+
+			if len(machine.IPAddresses) > 0 {
+				attrs.Add("device_ip", machine.IPAddresses[0].String())
+			}
+
+			resolver.Addr = fmt.Sprintf("%s?%s", resolver.Addr, attrs.Encode())
+		}
+	}
+}
+
 func getMapResponseDNSConfig(
 	dnsConfigOrig *tailcfg.DNSConfig,
 	baseDomain string,
 	machine Machine,
 	peers Machines,
 ) *tailcfg.DNSConfig {
-	var dnsConfig *tailcfg.DNSConfig
+	var dnsConfig *tailcfg.DNSConfig = dnsConfigOrig.Clone()
 	if dnsConfigOrig != nil && dnsConfigOrig.Proxied { // if MagicDNS is enabled
 		// Only inject the Search Domain of the current namespace - shared nodes should use their full FQDN
-		dnsConfig = dnsConfigOrig.Clone()
 		dnsConfig.Domains = append(
 			dnsConfig.Domains,
 			fmt.Sprintf(
@@ -184,5 +213,7 @@ func getMapResponseDNSConfig(
 		dnsConfig = dnsConfigOrig
 	}
 
+	addNextDNSMetadata(dnsConfig.Resolvers, machine)
+
 	return dnsConfig
 }