dns: nsupdate host records to the authoritative server

Replaces the exported-resources -> puppet DNS master zone-file flow with
per-host RFC2136 dynamic updates against the k8s bind-authoritative write
endpoint (198.18.200.9), so the master no longer manages zone files.

- add profiles::dns::updater: assembles the host's records into a concat
  file and runs nsupdate via a systemd .path unit that watches it; the
  dns-update script sends only the delta and deletes removed records
- switch profiles::dns::record to write local concat fragments
  (zone|name|type|ttl|value) instead of exporting to the master
- include profiles::dns::updater from profiles::dns::base (all nodes)
- inert until profiles::dns::updater::key_secret (TSIG) is set in eyaml
- hiera: updater server/key_name/algorithm in common.yaml

site/profiles/manifests/dns/base.pp

@@ -11,9 +11,12 @@ class profiles::dns::base (
   Optional[String] $ns_role = undef,
 ){
 
-  # install bind_utils
+  # install bind_utils (provides nsupdate)
   include bind::updater
 
+  # assemble the host's DNS records and nsupdate them to the authoritative server
+  include profiles::dns::updater
+
   # if ns_role is set, find all hosts matching that enc_role
   $nameserver_array = $ns_role ? {
     undef   => $nameservers,

site/profiles/manifests/dns/record.pp

@@ -1,4 +1,9 @@
-# defines the base record that will be exported
+# profiles::dns::record
+#
+# Declares a DNS record for this host. The record is written to the local
+# dns-updater records file (profiles::dns::updater), which nsupdates it to the
+# authoritative DNS server. This replaces the old flow that exported a
+# @@concat::fragment to the puppet DNS master.
 define profiles::dns::record (
   String  $record,
   Enum[
@@ -13,11 +18,14 @@ define profiles::dns::record (
   String  $value,
   String  $zone,
   Integer $order,
-  Stdlib::AbsolutePath $basedir = lookup('profiles::dns::master::basedir'),
+  Integer $ttl = 300,
 ) {
-  @@concat::fragment { "${zone}_${name}":
-    target  => "${basedir}/${zone}.conf",
-    content => "${record} IN ${type} ${value}\n",
-    order   => $order,
+  include profiles::dns::updater
+
+  # zone|name|type|ttl|value  (parsed by the dns-update script)
+  concat::fragment { "dns-record-${name}":
+    target  => $profiles::dns::updater::records_file,
+    content => "${zone}|${record}|${type}|${ttl}|${value}\n",
+    order   => sprintf('%03d', $order),
   }
 }

site/profiles/manifests/dns/updater.pp

@@ -0,0 +1,111 @@
+# profiles::dns::updater
+#
+# Applies this host's DNS records to the authoritative DNS server via TSIG
+# nsupdate, replacing the old exported-resources -> master zone-file flow.
+#
+# profiles::dns::record fragments are assembled into $records_file; a systemd
+# .path unit watches that file and runs dns-update.service (nsupdate) whenever
+# it changes. nsupdate comes from bind-utils (installed via bind::updater in
+# profiles::dns::base).
+#
+# Inert until $key_secret is set (the shared TSIG key that the k8s
+# bind-authoritative zones allow-update with): the records file is still
+# assembled, but the updater service is not managed, so nodes are safe before
+# the key is provisioned.
+class profiles::dns::updater (
+  String                      $server        = '198.18.200.9',
+  String                      $key_name      = 'client-update',
+  String                      $key_algorithm = 'hmac-sha256',
+  Optional[Sensitive[String]] $key_secret    = undef,
+  Integer                     $default_ttl   = 300,
+  Stdlib::AbsolutePath        $records_file  = '/var/lib/dns-updater/records',
+  Stdlib::AbsolutePath        $state_dir     = '/var/lib/dns-updater',
+  Stdlib::AbsolutePath        $config_dir    = '/etc/dns-updater',
+) {
+
+  $state_file = "${state_dir}/applied"
+  $key_file   = "${config_dir}/key"
+
+  file { $state_dir:
+    ensure => directory,
+    owner  => 'root',
+    group  => 'root',
+    mode   => '0755',
+  }
+
+  # Records file, assembled from profiles::dns::record fragments.
+  concat { $records_file:
+    ensure         => present,
+    owner          => 'root',
+    group          => 'root',
+    mode           => '0644',
+    ensure_newline => true,
+    warn           => false,
+    require        => File[$state_dir],
+  }
+
+  concat::fragment { 'dns-update-header':
+    target  => $records_file,
+    content => "# Managed by puppet (profiles::dns::record): zone|name|type|ttl|value\n",
+    order   => '00',
+  }
+
+  if $key_secret =~ Undef {
+    notify { 'dns-updater-inert':
+      message  => 'profiles::dns::updater: key_secret unset; records assembled but not applied.',
+      loglevel => 'info',
+    }
+  } else {
+    file { $config_dir:
+      ensure => directory,
+      owner  => 'root',
+      group  => 'root',
+      mode   => '0700',
+    }
+
+    file { $key_file:
+      ensure    => file,
+      owner     => 'root',
+      group     => 'root',
+      mode      => '0600',
+      show_diff => false,
+      content   => Sensitive(epp('profiles/dns/tsig-key.epp', {
+          'name'      => $key_name,
+          'algorithm' => $key_algorithm,
+          'secret'    => $key_secret.unwrap,
+      })),
+    }
+
+    file { '/usr/local/bin/dns-update':
+      ensure  => file,
+      owner   => 'root',
+      group   => 'root',
+      mode    => '0755',
+      content => epp('profiles/dns/dns-update.sh.epp', {
+          'server'       => $server,
+          'key_file'     => $key_file,
+          'records_file' => $records_file,
+          'state_file'   => $state_file,
+      }),
+    }
+
+    systemd::unit_file { 'dns-update.service':
+      content => epp('profiles/dns/dns-update.service.epp', { 'script' => '/usr/local/bin/dns-update' }),
+    }
+
+    # The .path unit watches the records file and triggers the service.
+    systemd::unit_file { 'dns-update.path':
+      content => epp('profiles/dns/dns-update.path.epp', { 'records_file' => $records_file }),
+      active  => true,
+      enable  => true,
+    }
+
+    # Also apply within the puppet run whenever the records change.
+    exec { 'dns-update-apply':
+      command     => '/usr/local/bin/dns-update',
+      refreshonly => true,
+      subscribe   => Concat[$records_file],
+      require     => [File['/usr/local/bin/dns-update'], File[$key_file]],
+    }
+  }
+}

site/profiles/templates/dns/dns-update.path.epp

@@ -0,0 +1,10 @@
+<%- | String $records_file | -%>
+[Unit]
+Description=Watch the DNS records file and apply changes
+
+[Path]
+PathModified=<%= $records_file %>
+Unit=dns-update.service
+
+[Install]
+WantedBy=multi-user.target

site/profiles/templates/dns/dns-update.service.epp

@@ -0,0 +1,9 @@
+<%- | String $script | -%>
+[Unit]
+Description=Apply host DNS records via nsupdate
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=<%= $script %>

site/profiles/templates/dns/dns-update.sh.epp

@@ -0,0 +1,56 @@
+<%- | String $server, String $key_file, String $records_file, String $state_file | -%>
+#!/bin/bash
+# Managed by puppet (profiles::dns::updater). Applies this host's records to the
+# authoritative DNS server via TSIG nsupdate. Only the delta since the last
+# successful run is sent; removed records are deleted.
+set -euo pipefail
+
+SERVER="<%= $server %>"
+KEYFILE="<%= $key_file %>"
+RECORDS="<%= $records_file %>"
+STATE="<%= $state_file %>"
+
+[ -f "$RECORDS" ] || exit 0
+touch "$STATE"
+
+# Format per line: zone|name|type|ttl|value  (name is relative to zone, or @).
+desired="$(grep -vE '^[[:space:]]*(#|$)' "$RECORDS" | sort -u || true)"
+applied="$(grep -vE '^[[:space:]]*(#|$)' "$STATE" 2>/dev/null | sort -u || true)"
+
+[ "$desired" = "$applied" ] && exit 0
+
+fqdn() { # name zone
+  if [ -z "$1" ] || [ "$1" = "@" ]; then printf '%s.' "$2"; else printf '%s.%s.' "$1" "$2"; fi
+}
+
+msg="$(mktemp)"
+trap 'rm -f "$msg"' EXIT
+printf 'server %s\n' "$SERVER" >> "$msg"
+
+# Process per zone so each UPDATE message targets a single zone.
+zones="$(printf '%s\n%s\n' "$desired" "$applied" | cut -d'|' -f1 | sort -u | grep -v '^$' || true)"
+for zone in $zones; do
+  printf 'zone %s.\n' "$zone" >> "$msg"
+  # Additions/updates: replace the RRset for every desired record in this zone.
+  printf '%s\n' "$desired" | awk -F'|' -v z="$zone" 'NF>=5 && $1==z' | \
+    while IFS='|' read -r z name type ttl value; do
+      f="$(fqdn "$name" "$z")"
+      printf 'update delete %s %s\n' "$f" "$type" >> "$msg"
+      printf 'update add %s %s %s %s\n' "$f" "$ttl" "$type" "$value" >> "$msg"
+    done
+  # Deletions: records present last run but gone now.
+  comm -23 <(printf '%s\n' "$applied") <(printf '%s\n' "$desired") | \
+    awk -F'|' -v z="$zone" 'NF>=5 && $1==z' | \
+    while IFS='|' read -r z name type ttl value; do
+      f="$(fqdn "$name" "$z")"
+      printf 'update delete %s %s %s\n' "$f" "$type" "$value" >> "$msg"
+    done
+  printf 'send\n' >> "$msg"
+done
+
+if nsupdate -k "$KEYFILE" "$msg"; then
+  printf '%s\n' "$desired" > "$STATE"
+else
+  echo "dns-update: nsupdate to ${SERVER} failed" >&2
+  exit 1
+fi

site/profiles/templates/dns/tsig-key.epp

@@ -0,0 +1,5 @@
+<%- | String $name, String $algorithm, String $secret | -%>
+key "<%= $name %>" {
+    algorithm <%= $algorithm %>;
+    secret "<%= $secret %>";
+};