feat: ship default catch-all site on fresh apt install

Fresh apt installs now drop a catch-all server block at `/etc/nginx/conf.d/00-default-vhost.conf` that uses `ssl_reject_handshake on` and `return 444` to drop requests with unknown Host headers. Conflicting upstream nginx default vhosts are renamed to `*.dokku-disabled` rather than deleted, preserving any local edits. The new `dokku/install_default_site` debconf flag opts out of the install. Upgrades leave existing nginx config untouched.

debian/config

@@ -14,5 +14,6 @@ db_input "high" "dokku/hostname" || true
 db_input "high" "dokku/vhost_enable" || true
 if [ "$ACTION" != "reconfigure" ]; then
   db_input "high" "dokku/key_file" || true
+  db_input "high" "dokku/install_default_site" || true
 fi
 db_go || true

debian/postinst

@@ -135,6 +135,38 @@ setup-sshcommand() {
   fi
 }
 
+setup-default-site() {
+  db_get "dokku/install_default_site"
+  if [ "$RET" != "true" ]; then
+    return
+  fi
+
+  local default_vhost_target="/etc/nginx/conf.d/00-default-vhost.conf"
+  local default_vhost_source="${DOKKU_LIB_ROOT}/core-plugins/available/nginx-vhosts/templates/default-site.conf"
+
+  if [ -e "$default_vhost_target" ]; then
+    return
+  fi
+
+  if [ ! -f "$default_vhost_source" ]; then
+    return
+  fi
+
+  for path in /etc/nginx/sites-enabled/default /etc/nginx/sites-available/default /etc/nginx/conf.d/default.conf; do
+    if [ -e "$path" ] && [ ! -e "${path}.dokku-disabled" ]; then
+      mv -n "$path" "${path}.dokku-disabled"
+      echo "Disabled $path (renamed to ${path}.dokku-disabled)" 1>&2
+    fi
+  done
+
+  echo "Installing nginx default catch-all site at $default_vhost_target"
+  install -m 0644 -o root -g root "$default_vhost_source" "$default_vhost_target"
+
+  if command -v dokku &>/dev/null; then
+    dokku nginx:reload || true
+  fi
+}
+
 dpkg-handling() {
   if [ -f "${DOKKU_ROOT}/VHOST" ]; then
     echo "VHOST file detected, skipping modification"
@@ -170,6 +202,9 @@ case "$1" in
     setup-plugins
     setup-sshcommand
     setup-docker-live-restore
+    if [ -z "$2" ]; then
+      setup-default-site
+    fi
     ;;
 
   *)

debian/templates

@@ -22,3 +22,8 @@ Template: dokku/nginx_enable
 Description: Enable nginx-vhosts plugin?
 Type: boolean
 Default: true
+
+Template: dokku/install_default_site
+Description: Install a catch-all nginx default site on fresh install?
+Type: boolean
+Default: true