99_google_set_hostname.sh

# Copyright 2021 Cloud Ace. All Rights Reserved.
# Author: Van Duong
# How To:
# /etc/NetworkManager/dispatcher.d/
# Centos: Copy file 99_google_set_hostname.sh to /etc/dhcp/dhclient.d/
# Debian: Copy file 99_google_set_hostname.sh to /etc/dhcp/dhclient-exit-hooks.d/
# Enable by add execute permission : chmod +x 99_google_set_hostname.sh
# Custom hostname by add metadata in GCE Instace: hostname: FQDN
#!/bin/bash
new_host_name=$(curl --fail --silent http://metadata.google.internal/computeMetadata/v1/instance/attributes/hostname  -H "Metadata-Flavor: Google")
new_ip_address=$(curl --fail --silent http://metadata.google.internal/computeMetadata/v1/instance/network-interfaces/0/ip  -H "Metadata-Flavor: Google")

if [ -n "$new_host_name" ] && [ -n "$new_ip_address" ]; then
  # Don't allow DHCP responses with the MDS as the hostname.
  # See: https://github.com/irsl/gcp-dhcp-takeover-code-exec
  if [[ "$new_host_name" =~ "metadata.google.internal" ]]; then
    echo 'not setting invalid hostname'
    exit 0
  fi

  # Delete entries with new_host_name or new_ip_address in /etc/hosts.
  sed -i"" '/Added by Google/d' /etc/hosts

  # Add an entry for our new_host_name/new_ip_address in /etc/hosts.
  echo "${new_ip_address} ${new_host_name} ${new_host_name%%.*}  # Added by Google" >> /etc/hosts
  echo "169.254.169.254 metadata.google.internal  # Added by Google" >> /etc/hosts
fi

if [ -n "$new_host_name" ]; then
  hostname "${new_host_name%%.*}"

  nmcli=$(which nmcli 2> /dev/null)
  if [ -x "$nmcli" ]; then
    nmcli general hostname "${new_host_name%%.*}"
  fi
fi