Merge pull request 'dns: introduce jpictl dns sync to update public DNS records' (#25)

A and AAAA only

Reviewed-on: #25

.vscode/settings.json

@@ -6,6 +6,9 @@
         "darvaza",
         "gofrs",
         "jpictl",
+        "libdns",
+        "Lookuper",
+        "publicsuffix",
         "Wrapf",
         "zerolog"
     ]

cmd/jpictl/dns.go

@@ -0,0 +1,132 @@
+package main
+
+import (
+	"context"
+	"os"
+	"time"
+
+	"github.com/spf13/cobra"
+
+	"git.jpi.io/amery/jpictl/pkg/cluster"
+	"git.jpi.io/amery/jpictl/pkg/dns"
+)
+
+const (
+	// DNSSyncTimeout specifies how long are we willing to wait for a DNS
+	// synchronization
+	DNSSyncTimeout = 10 * time.Second
+)
+
+func newDNSManager(m *cluster.Cluster, provider dns.Provider) (*dns.Manager, error) {
+	domain := m.Domain
+	if m.Name != "" {
+		domain = m.Name + "." + domain
+	}
+
+	mgr, err := dns.NewManager(dns.WithDomain(domain), dns.WithLogger(log))
+	if err != nil {
+		return nil, err
+	}
+
+	if provider != nil {
+		// set provider only  if specified
+		err = dns.WithProvider(provider)(mgr)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	if err := populateDNSManager(mgr, m); err != nil {
+		return nil, err
+	}
+
+	return mgr, nil
+}
+
+func populateDNSManager(mgr *dns.Manager, m *cluster.Cluster) error {
+	var err error
+
+	ctx := context.TODO()
+
+	m.ForEachZone(func(z *cluster.Zone) bool {
+		z.ForEachMachine(func(p *cluster.Machine) bool {
+			err = mgr.AddHost(ctx, z.Name, p.ID, true, p.PublicAddresses...)
+			return err != nil
+		})
+
+		return err != nil
+	})
+	if err != nil {
+		return err
+	}
+
+	m.ForEachRegion(func(r *cluster.Region) bool {
+		r.ForEachZone(func(z *cluster.Zone) bool {
+			err = mgr.AddRegion(ctx, r.Name, z.Name)
+			return err != nil
+		})
+
+		return err != nil
+	})
+
+	return err
+}
+
+// Command
+var dnsCmd = &cobra.Command{
+	Use: "dns",
+}
+
+var dnsWriteCmd = &cobra.Command{
+	Use:    "write",
+	Short:  "dns write generates public DNS records",
+	PreRun: setVerbosity,
+	RunE: func(_ *cobra.Command, _ []string) error {
+		m, err := cfg.LoadZones(true)
+		if err != nil {
+			return err
+		}
+
+		mgr, err := newDNSManager(m, nil)
+		if err != nil {
+			return err
+		}
+
+		_, err = mgr.WriteTo(os.Stdout)
+		return err
+	},
+}
+
+var dnsSyncCmd = &cobra.Command{
+	Use:    "sync",
+	Short:  "dns sync updates public DNS records",
+	PreRun: setVerbosity,
+	RunE: func(_ *cobra.Command, _ []string) error {
+		cred, err := dns.DefaultDNSProvider()
+		if err != nil {
+			return err
+		}
+
+		m, err := cfg.LoadZones(true)
+		if err != nil {
+			return err
+		}
+
+		mgr, err := newDNSManager(m, cred)
+		if err != nil {
+			return err
+		}
+
+		ctx, cancel := context.WithTimeout(context.Background(), DNSSyncTimeout)
+		defer cancel()
+
+		return mgr.Sync(ctx)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(dnsCmd)
+
+	dnsCmd.AddCommand(dnsWriteCmd)
+	dnsCmd.AddCommand(dnsSyncCmd)
+}

go.mod

@@ -11,9 +11,12 @@ require (
 	darvaza.org/slog/handlers/discard v0.4.5
 	github.com/gofrs/uuid/v5 v5.0.0
 	github.com/hack-pad/hackpadfs v0.2.1
+	github.com/libdns/cloudflare v0.1.0
+	github.com/libdns/libdns v0.2.1
 	github.com/mgechev/revive v1.3.3
 	github.com/spf13/cobra v1.7.0
 	golang.org/x/crypto v0.12.0
+	golang.org/x/net v0.14.0
 	gopkg.in/gcfg.v1 v1.2.3
 	gopkg.in/yaml.v3 v3.0.1
 )
@@ -39,7 +42,6 @@ require (
 	github.com/rs/zerolog v1.30.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	golang.org/x/mod v0.12.0 // indirect
-	golang.org/x/net v0.14.0 // indirect
 	golang.org/x/sys v0.12.0 // indirect
 	golang.org/x/text v0.13.0 // indirect
 	golang.org/x/tools v0.12.0 // indirect

go.sum

@@ -36,6 +36,11 @@ github.com/hack-pad/hackpadfs v0.2.1 h1:FelFhIhv26gyjujoA/yeFO+6YGlqzmc9la/6iKMI
 github.com/hack-pad/hackpadfs v0.2.1/go.mod h1:khQBuCEwGXWakkmq8ZiFUvUZz84ZkJ2KNwKvChs4OrU=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
 github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/libdns/cloudflare v0.1.0 h1:93WkJaGaiXCe353LHEP36kAWCUw0YjFqwhkBkU2/iic=
+github.com/libdns/cloudflare v0.1.0/go.mod h1:a44IP6J1YH6nvcNl1PverfJviADgXUnsozR3a7vBKN8=
+github.com/libdns/libdns v0.2.0/go.mod h1:yQCXzk1lEZmmCPa857bnk4TsOiqYasqpyOEeSObbb40=
+github.com/libdns/libdns v0.2.1 h1:Wu59T7wSHRgtA0cfxC+n1c/e+O3upJGWytknkmFEDis=
+github.com/libdns/libdns v0.2.1/go.mod h1:yQCXzk1lEZmmCPa857bnk4TsOiqYasqpyOEeSObbb40=
 github.com/mattn/go-colorable v0.1.12/go.mod h1:u5H1YNBxpqRaxsYJYSkiCWKzEfiAb1Gb520KVy5xxl4=
 github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
 github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=

pkg/cluster/regions.go

@@ -1,5 +1,10 @@
 package cluster
 
+var (
+	_ MachineIterator = (*Region)(nil)
+	_ ZoneIterator    = (*Region)(nil)
+)
+
 // Region represents a group of zones geographically related
 type Region struct {
 	m     *Cluster
@@ -9,6 +14,43 @@ type Region struct {
 	Regions []string `json:",omitempty" yaml:",omitempty"`
 }
 
+// ForEachRegion calls a function for each Region of the cluster
+// until instructed to terminate the loop
+func (m *Cluster) ForEachRegion(fn func(r *Region) bool) {
+	for i := range m.Regions {
+		r := &m.Regions[i]
+		if fn(r) {
+			return
+		}
+	}
+}
+
+// ForEachMachine calls a function for each Machine in the region
+// until instructed to terminate the loop
+func (r *Region) ForEachMachine(fn func(*Machine) bool) {
+	r.ForEachZone(func(z *Zone) bool {
+		var term bool
+
+		z.ForEachMachine(func(p *Machine) bool {
+			term = fn(p)
+			return term
+		})
+
+		return term
+	})
+}
+
+// ForEachZone calls a function for each Zone in the region
+// until instructed to terminate the loop
+func (r *Region) ForEachZone(fn func(*Zone) bool) {
+	for _, p := range r.zones {
+		if fn(p) {
+			// terminate
+			return
+		}
+	}
+}
+
 func (m *Cluster) initRegions(_ *ScanOptions) error {
 	regions := make(map[string][]*Zone)
 

pkg/dns/dns.go

@@ -0,0 +1,38 @@
+// Package dns manages DNS entries for the cluster
+package dns
+
+import (
+	"fmt"
+	"net/netip"
+)
+
+// Zone represents a set of hosts with high affinity
+type Zone struct {
+	Name string
+
+	Hosts map[int]*Host
+}
+
+func (z *Zone) String() string {
+	if z == nil {
+		return "undetermined"
+	}
+	return z.Name
+}
+
+// Host represents a member of the cluster
+type Host struct {
+	zone *Zone
+
+	ID     int
+	Active bool
+	Addrs  []netip.Addr
+}
+
+func (p *Host) String() string {
+	if p == nil {
+		return "undetermined"
+	}
+
+	return fmt.Sprintf("%s-%v", p.zone, p.ID)
+}

pkg/dns/manager.go

@@ -0,0 +1,173 @@
+package dns
+
+import (
+	"context"
+	"errors"
+	"io/fs"
+	"net/netip"
+	"strings"
+
+	"darvaza.org/core"
+	"darvaza.org/slog"
+	"git.jpi.io/amery/jpictl/pkg/cluster"
+	"golang.org/x/net/publicsuffix"
+)
+
+// Manager is a DNS Manager instance
+type Manager struct {
+	domain  string
+	suffix  string
+	zones   map[string]*Zone
+	regions map[string][]string
+
+	p Provider
+	l slog.Logger
+}
+
+// ManagerOption configures a Manager
+type ManagerOption func(*Manager) error
+
+func newErrorManagerOption(err error, hint string) ManagerOption {
+	return func(*Manager) error {
+		return core.Wrap(err, hint)
+	}
+}
+
+// WithProvider attaches a libdns Provider to the Manager
+func WithProvider(p Provider) ManagerOption {
+	var err error
+
+	if p == nil {
+		p, err = DefaultDNSProvider()
+	}
+
+	if err != nil {
+		return newErrorManagerOption(err, "WithProvider")
+	}
+
+	return func(mgr *Manager) error {
+		mgr.p = p
+		return nil
+	}
+}
+
+// WithLogger attaches a logger to the Manager
+func WithLogger(log slog.Logger) ManagerOption {
+	if log == nil {
+		log = cluster.DefaultLogger()
+	}
+
+	return func(mgr *Manager) error {
+		mgr.l = log
+		return nil
+	}
+}
+
+func (mgr *Manager) setDefaults() error {
+	var opts []ManagerOption
+
+	if mgr.l == nil {
+		opts = append(opts, WithLogger(nil))
+	}
+
+	if mgr.domain == "" || mgr.suffix == "" {
+		return errors.New("domain not specified")
+	}
+
+	for _, opt := range opts {
+		if err := opt(mgr); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// WithDomain specifies where the manager operates
+func WithDomain(domain string) ManagerOption {
+	base, err := publicsuffix.EffectiveTLDPlusOne(domain)
+	if err != nil {
+		return newErrorManagerOption(err, "publicsuffix")
+	}
+
+	suffix := strings.TrimSuffix(domain, base)
+	if suffix != "" {
+		suffix = "." + suffix[:len(suffix)-1]
+	}
+
+	return func(mgr *Manager) error {
+		mgr.domain = base
+		mgr.suffix = suffix
+		return nil
+	}
+}
+
+// NewManager creates a DNS manager with the
+func NewManager(opts ...ManagerOption) (*Manager, error) {
+	mgr := &Manager{
+		zones:   make(map[string]*Zone),
+		regions: make(map[string][]string),
+	}
+
+	for _, opt := range opts {
+		if err := opt(mgr); err != nil {
+			return nil, err
+		}
+	}
+
+	if err := mgr.setDefaults(); err != nil {
+		return nil, err
+	}
+	return mgr, nil
+}
+
+// AddHost registers a host
+func (mgr *Manager) AddHost(_ context.Context, zone string, id int,
+	active bool, addrs ...netip.Addr) error {
+	//
+	if zone == "" || id <= 0 {
+		return fs.ErrInvalid
+	}
+
+	z, ok := mgr.zones[zone]
+	if !ok {
+		z = &Zone{
+			Name:  zone,
+			Hosts: make(map[int]*Host),
+		}
+
+		mgr.zones[zone] = z
+	}
+
+	p := &Host{
+		zone:   z,
+		ID:     id,
+		Active: active,
+		Addrs:  SortAddrSlice(addrs),
+	}
+	z.Hosts[id] = p
+
+	if log, ok := mgr.l.Debug().WithEnabled(); ok {
+		log.WithField("subsystem", "dns").
+			WithField("zone", zone).
+			WithField("host", p.String()).
+			WithField("active", active).
+			Print()
+	}
+
+	return nil
+}
+
+// AddRegion specifies a new region and the zones it contains
+func (mgr *Manager) AddRegion(_ context.Context, region string, zones ...string) error {
+	mgr.regions[region] = append(mgr.regions[region], zones...)
+
+	if log, ok := mgr.l.Debug().WithEnabled(); ok {
+		for _, zoneName := range zones {
+			log.WithField("subsystem", "dns").
+				WithField("region", region).
+				WithField("zone", zoneName).Print()
+		}
+	}
+
+	return nil
+}

pkg/dns/provider.go

@@ -0,0 +1,38 @@
+package dns
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/libdns/cloudflare"
+	"github.com/libdns/libdns"
+)
+
+const (
+	// CloudflareAPIToken is the environment variable
+	// containing the API Token
+	CloudflareAPIToken = "CLOUDFLARE_DNS_API_TOKEN"
+)
+
+// Provider manages DNS entries
+type Provider interface {
+	libdns.RecordGetter
+	libdns.RecordDeleter
+	libdns.RecordSetter
+	libdns.RecordAppender
+}
+
+// DefaultDNSProvider returns a cloudflare DNS provider
+// using an API Token from env [CloudflareAPIToken]
+func DefaultDNSProvider() (*cloudflare.Provider, error) {
+	s := os.Getenv(CloudflareAPIToken)
+	if s == "" {
+		return nil, fmt.Errorf("%q: %s", CloudflareAPIToken, "not found")
+	}
+
+	p := &cloudflare.Provider{
+		APIToken: s,
+	}
+
+	return p, nil
+}

pkg/dns/record.go

@@ -0,0 +1,213 @@
+package dns
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/netip"
+	"sort"
+	"time"
+
+	"darvaza.org/core"
+	"github.com/libdns/libdns"
+)
+
+func (mgr *Manager) fqdn(name string) string {
+	return fmt.Sprintf("%s.%s.", name, mgr.domain)
+}
+
+// SortAddrSlice sorts a slice of [netip.Addr]
+func SortAddrSlice(s []netip.Addr) []netip.Addr {
+	sort.Slice(s, func(i, j int) bool {
+		return s[i].Less(s[j])
+	})
+	return s
+}
+
+// SortAddrRecords sorts a slice of [AddrRecord]
+// by Name and Address
+func SortAddrRecords(s []AddrRecord) []AddrRecord {
+	sort.Slice(s, func(i, j int) bool {
+		return s[i].Name < s[j].Name
+	})
+
+	for _, p := range s {
+		SortAddrSlice(p.Addr)
+	}
+
+	return s
+}
+
+// SortRegions sorts regions. first by length those 3-character
+// or shorter, and then by length. It's mostly aimed at
+// supporting ISO-3166 order
+func SortRegions(regions []string) []string {
+	sort.Slice(regions, func(i, j int) bool {
+		r1, r2 := regions[i], regions[j]
+
+		switch {
+		case len(r1) < 4:
+			switch {
+			case len(r1) < len(r2):
+				return true
+			case len(r1) > len(r2):
+				return false
+			default:
+				return r1 < r2
+			}
+		case len(r2) < 4:
+			return false
+		default:
+			return r1 < r2
+		}
+	})
+	return regions
+}
+
+// AddrRecord represents an A or AAAA record
+type AddrRecord struct {
+	Name string
+	Addr []netip.Addr
+}
+
+// Sort sorts the addresses of the record
+func (rr *AddrRecord) Sort() {
+	SortAddrSlice(rr.Addr)
+}
+
+// Export converts the record into libdns.Record
+func (rr *AddrRecord) Export() []libdns.Record {
+	out := make([]libdns.Record, len(rr.Addr))
+	for i, addr := range rr.Addr {
+		out[i] = libdns.Record{
+			Name:  rr.Name,
+			TTL:   time.Second * 1,
+			Type:  core.IIf(addr.Is6(), "AAAA", "A"),
+			Value: addr.String(),
+		}
+	}
+
+	return out
+}
+
+// WriteTo writes the record in BIND notation
+func (rr *AddrRecord) WriteTo(w io.Writer) (int64, error) {
+	var total int
+	for _, addr := range rr.Addr {
+		n, err := fmt.Fprint(w,
+			rr.Name, "\t",
+			1, "\t",
+			core.IIf(addr.Is6(), "AAAA", "A"), "\t",
+			addr.String(), "\n")
+
+		switch {
+		case err != nil:
+			return 0, err
+		case n > 0:
+			total += n
+		}
+	}
+
+	return int64(total), nil
+}
+
+// String converts the record into BIND entries
+func (rr *AddrRecord) String() string {
+	var buf bytes.Buffer
+	_, _ = rr.WriteTo(&buf)
+	return buf.String()
+}
+
+func (mgr *Manager) genRegionsSorted() []string {
+	regions := make([]string, 0, len(mgr.regions))
+	for name := range mgr.regions {
+		regions = append(regions, name)
+	}
+
+	return SortRegions(regions)
+}
+
+func (mgr *Manager) genAllAddrRecords() []AddrRecord {
+	var out []AddrRecord
+
+	cache := make(map[string][]netip.Addr)
+
+	// zones
+	for _, z := range mgr.zones {
+		// hosts
+		s := mgr.genZoneHostRecords(z)
+		out = append(out, s...)
+
+		// zone alias
+		addrs := mgr.genZoneAddresses(z)
+		name := z.Name
+
+		out = append(out, AddrRecord{
+			Name: name + mgr.suffix,
+			Addr: addrs,
+		})
+
+		// and cache for regions
+		cache[name] = addrs
+	}
+
+	for _, name := range mgr.genRegionsSorted() {
+		var addrs []netip.Addr
+
+		for _, z := range mgr.regions[name] {
+			addrs = append(addrs, cache[z]...)
+		}
+
+		rec := AddrRecord{
+			Name: name + mgr.suffix,
+			Addr: addrs,
+		}
+		rec.Sort()
+
+		out = append(out, rec)
+	}
+
+	SortAddrRecords(out)
+	return out
+}
+
+func (*Manager) genZoneAddresses(z *Zone) []netip.Addr {
+	var out []netip.Addr
+
+	for _, p := range z.Hosts {
+		if p.Active {
+			out = append(out, p.Addrs...)
+		}
+	}
+
+	SortAddrSlice(out)
+	return out
+}
+
+func (mgr *Manager) genZoneHostRecords(z *Zone) []AddrRecord {
+	out := make([]AddrRecord, 0, len(z.Hosts))
+
+	for _, p := range z.Hosts {
+		rec := AddrRecord{
+			Name: p.String() + mgr.suffix,
+			Addr: p.Addrs,
+		}
+		out = append(out, rec)
+	}
+
+	SortAddrRecords(out)
+	return out
+}
+
+func (mgr *Manager) genRegionAddressesCached(name string,
+	zones map[string][]netip.Addr) []netip.Addr {
+	//
+	var addrs []netip.Addr
+
+	for _, zoneName := range mgr.regions[name] {
+		addrs = append(addrs, zones[zoneName]...)
+	}
+
+	SortAddrSlice(addrs)
+	return addrs
+}

pkg/dns/sync.go

@@ -0,0 +1,347 @@
+package dns
+
+import (
+	"context"
+	"errors"
+	"net/netip"
+	"sort"
+	"strings"
+	"time"
+
+	"darvaza.org/core"
+	"darvaza.org/slog"
+	"github.com/libdns/libdns"
+)
+
+// SyncAddrRecord is similar to AddrRecord but include libdns.Record details
+// fetched from the Provider
+type SyncAddrRecord struct {
+	Name  string
+	Addrs []SyncAddr
+}
+
+// SyncAddr extends netip.Addr with ID and TTL fetched from the Provider
+type SyncAddr struct {
+	ID   string
+	Addr netip.Addr
+	TTL  time.Duration
+}
+
+// Export assembles a libdns.Record
+func (rec *SyncAddr) Export(name string) libdns.Record {
+	return libdns.Record{
+		ID:    rec.ID,
+		Name:  name,
+		Type:  core.IIf(rec.Addr.Is6(), "AAAA", "A"),
+		TTL:   time.Second,
+		Value: rec.Addr.String(),
+	}
+}
+
+// SortSyncAddrSlice sorts a slice of [SyncAddr] by its address
+func SortSyncAddrSlice(s []SyncAddr) []SyncAddr {
+	sort.Slice(s, func(i, j int) bool {
+		a1 := s[i].Addr
+		a2 := s[j].Addr
+		return a1.Less(a2)
+	})
+	return s
+}
+
+// GetRecords pulls all the address records on DNS for our domain
+func (mgr *Manager) GetRecords(ctx context.Context) ([]SyncAddrRecord, error) {
+	if mgr.p == nil {
+		return nil, errors.New("dns provider not specified")
+	}
+
+	recs, err := mgr.p.GetRecords(ctx, mgr.domain)
+	if err != nil {
+		return nil, err
+	}
+
+	return mgr.filteredRecords(recs)
+}
+
+// AsSyncAddr converts a A or AAAA [libdns.Record] into a [SyncAddr]
+func (mgr *Manager) AsSyncAddr(rr libdns.Record) (SyncAddr, bool, error) {
+	var out SyncAddr
+	var addr netip.Addr
+
+	// skip non-address types
+	if rr.Type != "A" && rr.Type != "AAAA" {
+		return out, false, nil
+	}
+
+	// skip entries not containing our suffix
+	if mgr.suffix != "" {
+		if !strings.HasSuffix(rr.Name, mgr.suffix) {
+			return out, false, nil
+		}
+	}
+
+	err := addr.UnmarshalText([]byte(rr.Value))
+	if err != nil {
+		// invalid address on A or AAAA record
+		return out, false, err
+	}
+
+	out = SyncAddr{
+		ID:   rr.ID,
+		TTL:  rr.TTL,
+		Addr: addr,
+	}
+
+	return out, true, nil
+}
+
+func (mgr *Manager) filteredRecords(recs []libdns.Record) ([]SyncAddrRecord, error) {
+	// filter and convert
+	cache := make(map[string][]SyncAddr)
+	for _, rr := range recs {
+		addr, ok, err := mgr.AsSyncAddr(rr)
+		switch {
+		case err != nil:
+			// skip invalid addresses
+			mgr.l.Error().
+				WithField("subsystem", "dns").
+				WithField(slog.ErrorFieldName, err).
+				WithField("name", rr.Name).
+				WithField("type", rr.Type).
+				WithField("addr", rr.Value).
+				Print()
+		case ok:
+			// store
+			cache[rr.Name] = append(cache[rr.Name], addr)
+		}
+	}
+
+	// prepare records
+	out := make([]SyncAddrRecord, len(cache))
+	names := make([]string, 0, len(cache))
+	for name := range cache {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+
+	for i, name := range names {
+		addrs := cache[name]
+
+		out[i] = SyncAddrRecord{
+			Name:  name,
+			Addrs: SortSyncAddrSlice(addrs),
+		}
+	}
+
+	return out, nil
+}
+
+// Sync updates all the address records on DNS for our domain
+func (mgr *Manager) Sync(ctx context.Context) error {
+	current, err := mgr.GetRecords(ctx)
+	if err != nil {
+		return core.Wrap(err, "GetRecords")
+	}
+
+	goal := mgr.genAllAddrRecords()
+	for _, p := range makeSyncMap(current, goal) {
+		err := mgr.doSync(ctx, p.Name, p.Before, p.After)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (mgr *Manager) doSync(ctx context.Context, name string,
+	before []SyncAddr, after []netip.Addr) error {
+	//
+	var err error
+
+	for _, a := range after {
+		before, err = mgr.doSyncUpdateOrInsert(ctx, name, a, before)
+		if err != nil {
+			return err
+		}
+	}
+
+	for _, b := range before {
+		err = mgr.doSyncRemove(ctx, name, b)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (mgr *Manager) doSyncUpdateOrInsert(ctx context.Context, name string,
+	addr netip.Addr, addrs []SyncAddr) ([]SyncAddr, error) {
+	//
+	var err error
+
+	i, ok := findSyncAddrSorted(addr, addrs)
+	if ok {
+		rec := addrs[i]
+
+		addrs = append(addrs[:i], addrs[i+1:]...)
+		err = mgr.doSyncUpdate(ctx, name, addr, rec)
+	} else {
+		err = mgr.doSyncInsert(ctx, name, addr)
+	}
+
+	return addrs, err
+}
+
+func (mgr *Manager) doSyncUpdate(ctx context.Context, name string,
+	addr netip.Addr, rec SyncAddr) error {
+	//
+	var log slog.Logger
+	var msg string
+	var err error
+
+	if rec.TTL != time.Second {
+		// amend TTL
+
+		// TODO: batch updates
+		_, err = mgr.p.SetRecords(ctx, mgr.domain, []libdns.Record{
+			rec.Export(name),
+		})
+
+		if err == nil {
+			log = mgr.l.Info()
+			msg = "Updated"
+		} else {
+			log = mgr.l.Error().
+				WithField(slog.ErrorFieldName, err)
+			msg = "Failed"
+		}
+	} else {
+		log = mgr.l.Info()
+		msg = "OK"
+	}
+
+	log.
+		WithField("subsystem", "dns").
+		WithField("name", name).
+		WithField("addr", addr).
+		Print(msg)
+
+	return err
+}
+
+func (mgr *Manager) doSyncInsert(ctx context.Context, name string,
+	addr netip.Addr) error {
+	//
+	var log slog.Logger
+	var msg string
+
+	rec := libdns.Record{
+		Name:  name,
+		Type:  core.IIf(addr.Is6(), "AAAA", "A"),
+		TTL:   time.Second,
+		Value: addr.String(),
+	}
+
+	_, err := mgr.p.AppendRecords(ctx, mgr.domain, []libdns.Record{
+		rec,
+	})
+
+	if err != nil {
+		log = mgr.l.Error().
+			WithField(slog.ErrorFieldName, err)
+		msg = "Failed to Add"
+	} else {
+		log = mgr.l.Info()
+		msg = "Added"
+	}
+
+	log.
+		WithField("subsystem", "dns").
+		WithField("name", name).
+		WithField("addr", addr).
+		Print(msg)
+	return err
+}
+
+func (mgr *Manager) doSyncRemove(ctx context.Context, name string,
+	rec SyncAddr) error {
+	//
+	var log slog.Logger
+	var msg string
+
+	// TODO: batch deletes
+	_, err := mgr.p.DeleteRecords(ctx, mgr.domain, []libdns.Record{
+		rec.Export(name),
+	})
+
+	if err != nil {
+		log = mgr.l.Error().
+			WithField(slog.ErrorFieldName, err)
+		msg = "Failed to Delete"
+	} else {
+		log = mgr.l.Warn()
+		msg = "Deleted"
+	}
+
+	log.
+		WithField("subsystem", "dns").
+		WithField("name", name).
+		WithField("addr", rec.Addr).
+		Print(msg)
+	return err
+}
+
+func findSyncAddrSorted(target netip.Addr, addrs []SyncAddr) (int, bool) {
+	for i, a := range addrs {
+		switch target.Compare(a.Addr) {
+		case 0:
+			// match
+			return i, true
+		case -1:
+			// miss
+			return -1, false
+		default:
+			// next
+		}
+	}
+
+	return -1, false
+}
+
+type syncMapEntry struct {
+	Name   string
+	Before []SyncAddr
+	After  []netip.Addr
+}
+
+func makeSyncMap(current []SyncAddrRecord,
+	goal []AddrRecord) map[string]syncMapEntry {
+	//
+	data := make(map[string]syncMapEntry)
+
+	for _, cur := range current {
+		me, ok := data[cur.Name]
+		if !ok {
+			me = syncMapEntry{
+				Name: cur.Name,
+			}
+		}
+
+		me.Before = append(me.Before, cur.Addrs...)
+		data[cur.Name] = me
+	}
+
+	for _, rr := range goal {
+		me, ok := data[rr.Name]
+		if !ok {
+			me = syncMapEntry{
+				Name: rr.Name,
+			}
+		}
+		me.After = append(me.After, rr.Addr...)
+		data[rr.Name] = me
+	}
+
+	return data
+}

pkg/dns/write.go

@@ -0,0 +1,62 @@
+package dns
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/netip"
+)
+
+// WriteTo writes the DNS data for the cluster
+func (mgr *Manager) WriteTo(w io.Writer) (int64, error) {
+	var buf bytes.Buffer
+
+	cache := make(map[string][]netip.Addr)
+
+	// zones
+	for _, z := range mgr.zones {
+		mgr.writeZoneHosts(&buf, z)
+
+		// zone alias
+		addrs := mgr.genZoneAddresses(z)
+		zoneName := z.Name
+
+		rr := AddrRecord{
+			Name: mgr.fqdn(zoneName + mgr.suffix),
+			Addr: addrs,
+		}
+		_, _ = rr.WriteTo(&buf)
+
+		// and cache for regions
+		cache[zoneName] = addrs
+	}
+
+	// regions, sorted
+	for _, name := range mgr.genRegionsSorted() {
+		addrs := mgr.genRegionAddressesCached(name, cache)
+
+		mgr.writeRegionAddresses(&buf, name, addrs)
+	}
+
+	return buf.WriteTo(w)
+}
+
+func (mgr *Manager) writeZoneHosts(w io.Writer, z *Zone) {
+	_, _ = fmt.Fprintf(w, ";\n; %s\n;\n", z.Name)
+
+	for _, rr := range mgr.genZoneHostRecords(z) {
+		rr.Name = mgr.fqdn(rr.Name)
+		_, _ = rr.WriteTo(w)
+	}
+}
+
+func (mgr *Manager) writeRegionAddresses(w io.Writer, name string, addrs []netip.Addr) {
+	_, _ = fmt.Fprintf(w, "; %s\n", name)
+
+	rr := AddrRecord{
+		Name: mgr.fqdn(name + mgr.suffix),
+		Addr: addrs,
+	}
+
+	_, _ = rr.WriteTo(w)
+}