build.func: set DNS from VLAN tag via network profile (incl. DHCP)

Adds apply_network_profile(), which looks up DNS servers for the entered
VLAN tag in lib/networks.conf and sets --nameserver accordingly — even
when IP is DHCP. Precedence: explicit env NAMESERVER > profile > static
prompt > inherit. Comma-separated DNS is normalised to spaces for pct.

lib/build.func

@@ -36,6 +36,12 @@ DEFAULT_ROOTFS_STORAGE="${DEFAULT_ROOTFS_STORAGE:-local-lvm}"
 DEFAULT_TEMPLATE_PATTERN="${DEFAULT_TEMPLATE_PATTERN:-debian-12-standard}"
 DEFAULT_NAMESERVER="${DEFAULT_NAMESERVER:-}"
 
+# Network profiles: map a VLAN tag → DNS servers (+ subnet), maintained in
+# lib/networks.conf so adding a network is a one-line change. Applied even for
+# DHCP, so every container gets the right resolvers for its VLAN.
+NET_PROFILES_URL="${NET_PROFILES_URL:-https://gitea.luki-net.org/luki-net/proxmox-scripts/raw/branch/main/lib/networks.conf}"
+# Set NET_PROFILES_FILE to a local path to use that instead of the remote file.
+
 # ── error trap ───────────────────────────────────────────────────────────────
 _on_error() {
   local exit_code=$?
@@ -63,6 +69,34 @@ show_header() {
   echo
 }
 
+# ── network profiles ─────────────────────────────────────────────────────────
+# Look up DNS servers for the chosen VLAN tag from lib/networks.conf.
+# Sets PROFILE_DNS (space-separated, ready for pct --nameserver) and
+# PROFILE_SUBNET. Both stay empty if there's no matching profile.
+apply_network_profile() {
+  PROFILE_DNS=""; PROFILE_SUBNET=""
+  local key="${VLAN_TAG:-}"; [[ -z "$key" ]] && key="none"
+
+  local data=""
+  if [[ -n "${NET_PROFILES_FILE:-}" && -r "${NET_PROFILES_FILE:-}" ]]; then
+    data=$(cat "$NET_PROFILES_FILE")
+  else
+    data=$(curl -fsSL "$NET_PROFILES_URL" 2>/dev/null) || data=""
+  fi
+  [[ -n "$data" ]] || { msg_warn "Could not load network profiles ($NET_PROFILES_URL)"; return 0; }
+
+  local t s d _rest
+  while read -r t s d _rest; do
+    [[ -z "$t" || "$t" == \#* ]] && continue          # skip blanks/comments
+    if [[ "$t" == "$key" ]]; then
+      PROFILE_SUBNET="$s"
+      PROFILE_DNS="${d//,/ }"                          # pct wants space-separated
+      return 0
+    fi
+  done <<< "$data"
+  return 0
+}
+
 # ── prompts ──────────────────────────────────────────────────────────────────
 # Each prompt is skipped if the corresponding variable is already set in env.
 # VLAN_TAG and NAMESERVER use ${VAR+x} so that explicitly setting them to ""
@@ -113,12 +147,24 @@ prompt_lxc_config() {
   if [[ "$IPCFG" != "dhcp" && -z "$GATEWAY" ]]; then
     read -rp "Gateway: " GATEWAY
   fi
-  # DNS: only meaningful for static IPs (DHCP gets DNS from the lease).
-  # Default suggestion is the gateway, which doubles as DNS in most homelabs.
-  if [[ "$IPCFG" != "dhcp" && -z "${NAMESERVER+x}" ]]; then
+  # DNS is driven by the VLAN tag via the network profile (lib/networks.conf),
+  # so the right resolvers get set even with DHCP. Precedence:
+  #   1. explicit NAMESERVER from env (even "" = inherit)  → respected as-is
+  #   2. profile match for this VLAN tag                   → use its DNS
+  #   3. static IP, no profile                             → ask
+  #   4. DHCP, no profile                                  → inherit from host
+  apply_network_profile
+  if [[ -n "${NAMESERVER+x}" ]]; then
+    :  # explicit override from env, leave untouched
+  elif [[ -n "$PROFILE_DNS" ]]; then
+    NAMESERVER="$PROFILE_DNS"
+    msg_info "DNS for VLAN ${VLAN_TAG:-none} (${PROFILE_SUBNET:-?}): $NAMESERVER"
+  elif [[ "$IPCFG" != "dhcp" ]]; then
     local default_ns="${DEFAULT_NAMESERVER:-$GATEWAY}"
     read -rp "DNS server [$default_ns] (empty = inherit from PVE host): " NAMESERVER
     NAMESERVER="${NAMESERVER:-$default_ns}"
+  else
+    msg_warn "No network profile for VLAN ${VLAN_TAG:-none}; DHCP DNS will be inherited."
   fi
 }
 
@@ -165,11 +211,11 @@ create_lxc() {
     --ostype debian
     --password "$ROOT_PASSWORD"
   )
-  [[ -n "${NAMESERVER:-}" ]] && pct_args+=(--nameserver "$NAMESERVER")
+  [[ -n "${NAMESERVER:-}" ]] && pct_args+=(--nameserver "${NAMESERVER//,/ }")
 
   msg_info "Creating unprivileged LXC $CTID ($CT_HOSTNAME)..."
   msg_info "  net0: $net_opts"
-  [[ -n "${NAMESERVER:-}" ]] && msg_info "  dns:  $NAMESERVER"
+  [[ -n "${NAMESERVER:-}" ]] && msg_info "  dns:  ${NAMESERVER//,/ }"
   pct create "${pct_args[@]}"
   msg_ok "LXC $CTID created"