netcup: dns fixes

scripts/installer.sh

@@ -80,14 +80,28 @@ fi
 
 # switch over to resolved and uninstall resolvconf
 if dpkg -s resolvconf 2>/dev/null >/dev/null; then
+    vendor=$(cat /sys/devices/virtual/dmi/id/sys_vendor || true)
+
+    prepare_apt_once # do this first before DNS goes away intermittently
+
     log "disabling unbound"
     systemctl disable unbound || true
     systemctl stop unbound || true
+
     log "enabling systemd-resolved"
     systemctl enable --now systemd-resolved
+
     log "removing resolvconf"
-    prepare_apt_once
+    [[ "${vendor}" == "netcup" && -f /etc/resolvconf/resolv.conf.d/original ]] && cp /etc/resolvconf/resolv.conf.d/original /tmp/resolv.conf.original # stash before purging
     apt -y --purge remove resolvconf # purge required for dpkg -s to return error code
+
+    if [[ "${vendor}" == "netcup" && -f /tmp/resolv.conf.original ]]; then
+        log "Fix netcup DNS setup"
+        nameservers=$(sed -ne 's/nameserver \(.*\)/"\1"/p' /tmp/resolv.conf.original | paste -sd "," -) # json array
+        netplan set --origin-hint 50-cloud-init  "ethernets.eth0.nameservers.addresses=[${nameservers}]"
+        netplan apply # generates /run/systemd/resolve/resolv.conf
+        systemctl restart systemd-resolved
+    fi
 fi
 
 # https://docs.docker.com/engine/installation/linux/ubuntulinux/