config.cfg

@@ -18,6 +18,12 @@ records = [
     # specify that auth.example.org will resolve any *.auth.example.org records
     "auth.example.org. NS auth.example.org.",
 ]
+# path to cache SOA serial
+serialpath = "soa-serial.save"
+# slaves to notify on update and allowed to request AXFR
+slaves = [
+    # "10.5.1.1"
+]
 # debug messages from CORS etc
 debug = false
 

pkg/acmedns/interfaces.go

@@ -21,4 +21,6 @@ type AcmednsNS interface {
 	SetOwnAuthKey(key string)
 	SetNotifyStartedFunc(func())
 	ParseRecords()
+	BumpSerial() error
+}
 }

pkg/acmedns/types.go

@@ -25,6 +25,8 @@ type general struct {
 	Nsadmin       string
 	Debug         bool
 	StaticRecords []string `toml:"records"`
+	Serialpath    string
+	SlaveHosts    []string `toml:"slaves"`
 }
 
 type dbsettings struct {

pkg/api/api.go

@@ -15,10 +15,11 @@ import (
 )
 
 type AcmednsAPI struct {
-	Config  *acmedns.AcmeDnsConfig
-	DB      acmedns.AcmednsDB
-	Logger  *zap.SugaredLogger
-	errChan chan error
+	Config     *acmedns.AcmeDnsConfig
+	DB         acmedns.AcmednsDB
+	Logger     *zap.SugaredLogger
+	errChan    chan error
+	dnsServers []acmedns.AcmednsNS
 }
 
 func Init(config *acmedns.AcmeDnsConfig, db acmedns.AcmednsDB, logger *zap.SugaredLogger, errChan chan error) AcmednsAPI {
@@ -27,6 +28,8 @@ func Init(config *acmedns.AcmeDnsConfig, db acmedns.AcmednsDB, logger *zap.Sugar
 }
 
 func (a *AcmednsAPI) Start(dnsservers []acmedns.AcmednsNS) {
+	//we need the dnsservers later to bump serial
+	a.dnsServers = dnsservers
 	var err error
 	//TODO: do we want to debug log the HTTP server?
 	stderrorlog, err := zap.NewStdLogAt(a.Logger.Desugar(), zap.ErrorLevel)

pkg/api/update.go

@@ -49,6 +49,10 @@ func (a *AcmednsAPI) webUpdatePost(w http.ResponseWriter, r *http.Request, _ htt
 			upd = []byte("{\"txt\": \"" + atxt.Value + "\"}")
 		}
 	}
+	for _, s := range a.dnsServers {
+		//bump SOA serial on update (and notify slaves if configured)
+		s.BumpSerial()
+	}
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(updStatus)
 	_, _ = w.Write(upd)

pkg/nameserver/handler.go

@@ -71,6 +71,9 @@ func (n *Nameserver) answer(q dns.Question) ([]dns.RR, int, bool, error) {
 			r = append(r, txtRRs...)
 		}
 	}
+	if q.Qtype == dns.TypeSOA {
+		r = append(r, n.SOA)
+	}
 	if len(r) > 0 {
 		// Make sure that we return NOERROR if there were dynamic records for the domain
 		rcode = dns.RcodeSuccess

pkg/nameserver/initialize.go

@@ -14,6 +14,7 @@ import (
 // Records is a slice of ResourceRecords
 type Records struct {
 	Records []dns.RR
+	NS      []dns.RR
 }
 
 type Nameserver struct {
@@ -23,7 +24,7 @@ type Nameserver struct {
 	Server            *dns.Server
 	OwnDomain         string
 	NotifyStartedFunc func()
-	SOA               dns.RR
+	SOA               *dns.SOA
 	mu                sync.RWMutex
 	personalAuthKey   string
 	Domains           map[string]Records

pkg/nameserver/parseconfig.go

@@ -2,12 +2,64 @@ package nameserver
 
 import (
 	"fmt"
+	"os"
+	"strconv"
 	"strings"
 	"time"
 
 	"github.com/miekg/dns"
 )
 
+func loadSerial(path string) (uint32, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return 0, nil // first start
+		}
+		return 0, err
+	}
+
+	s := strings.TrimSpace(string(data))
+	val, err := strconv.ParseUint(s, 10, 32)
+	if err != nil {
+		return 0, err
+	}
+
+	return uint32(val), nil
+}
+
+func saveSerial(path string, serial uint32) error {
+	tmp := path + ".tmp"
+
+	data := []byte(fmt.Sprintf("%d\n", serial))
+
+	// write temp file
+	if err := os.WriteFile(tmp, data, 0644); err != nil {
+		return err
+	}
+
+	// atomic replace
+	return os.Rename(tmp, path)
+}
+
+func nextSerial(old uint32) uint32 {
+	today := time.Now().Format("20060102")
+
+	oldStr := fmt.Sprintf("%d", old)
+
+	if strings.HasPrefix(oldStr, today) {
+		return old + 1
+	}
+
+	newSerial, _ := strconv.Atoi(today + "00")
+
+	if uint32(newSerial) <= old {
+		return old + 1
+	}
+
+	return uint32(newSerial)
+}
+
 // ParseRecords parses a slice of DNS record string
 func (n *Nameserver) ParseRecords() {
 	for _, v := range n.Config.General.StaticRecords {
@@ -22,25 +74,72 @@ func (n *Nameserver) ParseRecords() {
 		n.appendRR(rr)
 	}
 	// Create serial
-	serial := time.Now().Format("2006010215")
-	// Add SOA
-	SOAstring := fmt.Sprintf("%s. SOA %s. %s. %s 28800 7200 604800 86400", strings.ToLower(n.Config.General.Domain), strings.ToLower(n.Config.General.Nsname), strings.ToLower(n.Config.General.Nsadmin), serial)
-	soarr, err := dns.NewRR(SOAstring)
+	serial, err := loadSerial(n.Config.General.Serialpath)
+
 	if err != nil {
-		n.Logger.Errorw("Error while adding SOA record",
-			"error", err.Error(),
-			"soa", SOAstring)
-	} else {
-		n.appendRR(soarr)
-		n.SOA = soarr
+		n.Logger.Errorw("Could not load temp serial",
+			"error", err.Error())
 	}
+	if serial == 0 {
+		serial = uint32(time.Now().Unix())
+	}
+	// Add SOA
+	//Refresh = 30s → Slaves fragen alle 30s nach Änderungen
+	//Retry = 10s → Wenn Master nicht erreichbar, probiert der Slave alle 10s erneut
+	//Expire = 604800s (1w) → Wie lange der Slave die Zone noch behält, falls Master ausfällt
+	//Minimum TTL = 20s → Resolver cachen die TXT-Einträge nur kurz
+	//SOAstring := fmt.Sprintf("%s. SOA %s. %s. %s 5 10 604800 20", strings.ToLower(n.Config.General.Domain), strings.ToLower(n.Config.General.Nsname), strings.ToLower(n.Config.General.Nsadmin), serial)
+	n.SOA = &dns.SOA{
+		Hdr: dns.RR_Header{
+			Name:   dns.Fqdn(n.Config.General.Domain),
+			Rrtype: dns.TypeSOA,
+			Class:  dns.ClassINET,
+			Ttl:    5,
+		},
+		Ns:      dns.Fqdn(n.Config.General.Nsname),
+		Mbox:    dns.Fqdn(n.Config.General.Nsadmin),
+		Serial:  serial,
+		Refresh: 5,
+		Retry:   10,
+		Expire:  604800,
+		Minttl:  1,
+	}
+}
+
+func sendNotify(zone string, slaveAddr string) error {
+	m := new(dns.Msg)
+	m.SetNotify(dns.Fqdn(zone)) // Set opcode to NOTIFY
+	m.Authoritative = true      // Must be authoritative
+
+	c := new(dns.Client)
+	_, _, err := c.Exchange(m, slaveAddr)
+	return err
+}
+
+func (n *Nameserver) BumpSerial() error {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	n.SOA.Serial = nextSerial(n.SOA.Serial)
+
+	for _, slave := range n.Config.General.SlaveHosts {
+		slave := slave + ":53"
+		if err := sendNotify(n.SOA.Hdr.Name, slave); err != nil {
+			n.Logger.Errorw("Failed to notify slave", "slave", slave, "err", err)
+		} else {
+			n.Logger.Debugw("Notify send to slave", "slave", slave)
+		}
+	}
+	return saveSerial(n.Config.General.Serialpath, n.SOA.Serial)
 }
 
 func (n *Nameserver) appendRR(rr dns.RR) {
 	addDomain := rr.Header().Name
 	_, ok := n.Domains[addDomain]
 	if !ok {
-		n.Domains[addDomain] = Records{[]dns.RR{rr}}
+		n.Domains[addDomain] = Records{
+			Records: []dns.RR{rr}, // initialisiere Records
+			NS:      []dns.RR{},   // leeres NS-Slice, sonst Fehler
+		}
 	} else {
 		drecs := n.Domains[addDomain]
 		drecs.Records = append(drecs.Records, rr)