dynamic-ip-refresh.sh

#!/usr/bin/env bash

# Requirements: curl, jq (sudo apt install curl jq)

# First, create an A record manually with a TTL of 120 (2 minutes, the minimum)

# The API key is generated from Vultr's user dashboard.
# The Record ID is a UUID, fetch it from here:
#   curl -H "Authorization: Bearer ${VULTR_API_KEY}" https://api.vultr.com/v2/domains/${VULTR_DOMAIN}/records

# Save the script under /opt/dynamic-ip-refresh.sh and create a root cron entry to run it every 3rd minute:
#   */3 * * * * /opt/dynamic-ip-refresh.sh

VULTR_API_KEY=<your API key>
VULTR_DOMAIN=<example.com>
VULTR_VPN_RECORD_ID=<subdomain id>

CURRENT_IP=$(curl -s https://ip.1mahq.com/)

DNS_IP=$(curl -s -H "Authorization: Bearer ${VULTR_API_KEY}" -X GET https://api.vultr.com/v2/domains/${VULTR_DOMAIN}/records/${VULTR_VPN_RECORD_ID} | jq -r .record.data)

if [ "$CURRENT_IP" = "$DNS_IP" ]; then
    echo "IP ${CURRENT_IP} hasn't changed, exiting."
    exit 0
fi

echo "IP changed from ${DNS_IP} to ${CURRENT_IP}, updating DNS record."
echo

curl -i -s \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer ${VULTR_API_KEY}" \
  --data "{\"data\": \"${CURRENT_IP}\"}" \
  -X PATCH https://api.vultr.com/v2/domains/${VULTR_DOMAIN}/records/${VULTR_VPN_RECORD_ID}