Monitor the Bandwidth Used by your Digital Ocean droplet

monitor.service

#
# monitor-bandwidth.service
#
[Unit]
Description=Ocean Network Allocation Monitor
After=network.target
Requires=network.target

[Service]
Type=simple
ExecStart=/usr/local/bin/monitor.sh
ExecStop=/usr/bin/pkill -TERM monitor.sh
User=<your_username>
Group=<your_username>
UMask=002
StandardOutput=syslog
StandardError=inherit
SyslogFacility=local0
Restart=always
RestartSec=30

[Install]
WantedBy=multi-user.target

monitor.sh

#!/usr/bin/env bash

#
# Copyright 2021 Vallum Software, LLC. MIT license.
#

#
# Send an alert when network traffic allocation exceeds 900 GiB
#

webhook_url=''

while [ true ]
do
    traffic=$(vnstat --oneline | awk -F ";" '{print $11}')
    if [[ "${traffic}" == "GiB" ]]
    then
	    if [ $(echo "$(echo "${traffic}" | sed 's/ GiB//g') > 900" | bc) -eq 1 ]
	    then
	        curl -X POST -H 'Content-type: application/json' --data "{\"text\":\"Traffic level ${traffic}\"}" ${webhook_url}
	    fi
    fi
    sleep 600
done

exit 0