fix: handle Postfix DNS resolution after switching to BIND9

switch-resolver-to-bind9.sh

@@ -11,7 +11,7 @@ readonly NSS=/etc/nsswitch.conf
 readonly EXPECTED_NSS='hosts:          files myhostname dns'
 
 MODE="${1:---check}"
-case "$MODE" in --check|--apply|--rollback|--help) ;; *) echo "Usage: $0 [--check|--apply|--rollback|--help]" >&2; exit 2;; esac
+case "$MODE" in --check|--apply|--rollback|--repair-postfix|--help) ;; *) echo "Usage: $0 [--check|--apply|--rollback|--repair-postfix|--help]" >&2; exit 2;; esac
 
 # Colorize status labels on terminals; respect NO_COLOR and redirected output.
 if [[ -t 1 && ! -v NO_COLOR && "${TERM:-}" != dumb ]]; then
@@ -78,6 +78,60 @@ preflight(){
   if grep -q 'status: SERVFAIL' <<< "$reply"; then ok 'rejected as expected'; else echo; failed 'BIND9 does not reject invalid DNSSEC test zone'; return 1; fi
 }
 
+# Debian Postfix: systemd instance startup refreshes the chroot resolver files.
+# This is deliberately limited to running Postfix instances. No data_directory
+# files are ever removed. A queue flush remains a separate admin decision.
+postfix_units(){
+  local unit
+  while read -r unit _; do
+    [[ "$unit" == postfix@*.service ]] || continue
+    printf '%s\n' "$unit"
+  done < <(systemctl list-units --type=service --state=active --no-legend --plain 'postfix@*.service' 2>/dev/null)
+}
+
+sync_postfix(){
+  local -a units=()
+  local unit queue_dir chroot_resolv
+  if ! command -v postconf >/dev/null 2>&1; then
+    skipped 'Postfix not installed; no MTA restart required'
+    return 0
+  fi
+  mapfile -t units < <(postfix_units)
+  if (( ${#units[@]} == 0 )); then
+    if systemctl is-active --quiet postfix.service; then
+      units=(postfix.service)
+    else
+      skipped 'No active Postfix service; no MTA restart required'
+      return 0
+    fi
+  fi
+  info 'Restarting active Postfix systemd service(s) to refresh chroot DNS'
+  for unit in "${units[@]}"; do
+    systemctl restart "$unit" || { failed "Postfix restart failed: $unit"; return 1; }
+    if ! systemctl is-active --quiet "$unit"; then
+      failed "Postfix service not active after restart: $unit"
+      return 1
+    fi
+    ok "Postfix restarted: $unit"
+  done
+  # Only assert a chroot resolver copy when it exists; custom setups may
+  # use multiple queue directories or run SMTP clients without chroot.
+  queue_dir=$(postconf -h queue_directory 2>/dev/null || true)
+  if [[ -n "$queue_dir" && -f "$queue_dir/etc/resolv.conf" ]]; then
+    chroot_resolv="$queue_dir/etc/resolv.conf"
+    if cmp -s "$RESOLV" "$chroot_resolv"; then
+      ok "Postfix chroot resolver synchronized: $chroot_resolv"
+    else
+      failed "Postfix chroot resolver differs: $chroot_resolv"
+      failed 'Check Debian postfix configure-instance.sh / active instances'
+      return 1
+    fi
+  else
+    info 'No default Postfix chroot resolv.conf found (possibly non-chroot or custom layout)'
+  fi
+  info 'Deferred mail is not flushed automatically; if appropriate run: postqueue -f'
+}
+
 show_check(){
   require_root
   need dig; need systemctl; need getent
@@ -145,6 +199,7 @@ rollback_to(){
   restore_files "$path"
   restore_services "$path"
   ok 'Configuration and resolved service state restored'
+  sync_postfix
 }
 
 apply(){
@@ -166,7 +221,7 @@ apply(){
   status_banner "$GREEN" 'Umstellung kann durchgeführt werden.' \
       "Ausführen mit: $0 --apply"
   printf '\nPlanned changes:\n  hosts: files myhostname dns\n  resolv.conf: nameserver 127.0.0.1\n  stop and disable systemd-resolved\n'
-  info 'Network interfaces, routes, BIND9 and MTA are not changed.'
+  info 'Network interfaces, routes and BIND9 are unchanged; active Postfix will restart.'
   confirm || { skipped 'Abbruch durch User'; exit 0; }
 
   mkdir -p "$STATE_DIR"
@@ -216,11 +271,25 @@ apply(){
   echononl 'systemd-resolved disabled'
   is_fully_switched && ok 'yes' || { echo; false; }
   preflight
+  sync_postfix
   trap - ERR INT TERM
   ok 'Switch completed successfully' 
   info "Rollback available: $0 --rollback"
 }
 
+repair_postfix(){
+  require_root
+  need systemctl; need postconf; need cmp
+  if ! is_direct; then
+    fatal 'Resolver is not configured for direct BIND9; use --check first'
+  fi
+  if ! preflight; then
+    fatal 'Local DNSSEC preflight failed; Postfix unchanged'
+  fi
+  sync_postfix
+  ok 'Postfix DNS synchronization completed'
+}
+
 rollback(){
   require_root
   local path
@@ -235,15 +304,18 @@ rollback(){
 case "$MODE" in
   --help)
     cat <<'HELP'
-Usage: switch-resolver-to-bind9.sh [--check|--apply|--rollback|--help]
+Usage: switch-resolver-to-bind9.sh [--check|--apply|--rollback|--repair-postfix|--help]
   --check     read-only checks (default)
   --apply     verify BIND9 DNSSEC; back up; switch DNS/NSS; stop+disable resolved
   --rollback  restore files and resolved service state saved before last --apply
+  --repair-postfix  restart active Postfix instance(s) to refresh chroot DNS
   --help      this help
+After Postfix restart: consider postqueue -f to retry deferred messages.
 Notes: run as root; requires BIND9 already working; no package changes.
 HELP
     ;;
   --check) show_check ;;
   --apply) apply ;;
   --rollback) rollback ;;
+  --repair-postfix) repair_postfix ;;
 esac