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/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]],
+    }
+  }
+}