Script for automatically updating the DNS record in CloudFlare, for dynamic DNS.

update-dns.sh

#!/bin/bash

# Dynamic DNS auto-update script for CloudFlare API
# Version 3 - Ryan Crosby 2023
#
# Supports IPv4 and IPv6 (A and AAAA records)
#
# Requires curl and jq

echo "Dynamic DNS auto-update script for CloudFlare API"
echo "Version 3"

# =====================
# CONFIGURATION
# =====================

# The name of the interface that holds your public IP address. Eg. enp1s0 or eth0.
INTERFACE_NAME="enp1s0"

# The name of the A and/or AAAA record to be updated.
DNS_ADDRESS="your.dns.record.name.com"

# The CloudFlare API token used to access the API. Must have DNS Zone Read/Write capabilities.
CLOUDFLARE_API_TOKEN="YOUR_CLOUDFLARE_DNS_ZONE_WRITE_TOKEN"

# The CloudFlare API Zone ID
ZONE_ID="YOUR_CLOUDFLARE_ZONE_ID"

# CloudFlare API URL
CLOUDFLARE_HOST="https://api.cloudflare.com"

# =====================

# Do case insensitive string comparisons in if statements
# IPv6 is technically case insensitive so it's easier just to do all comparisons case insensitive.
shopt -s nocasematch

# =====================
# Functions
# =====================

# Returns an interface's global (aka public) IP address.
# Arg 1: Interface Name
# Arg 2: Protocol Family (inet = IPv4, inet6 = IPv6)
get_my_ip() {
        # Get public IP address from the internet facing interface
        ip -json -family ${2} address show dev ${1} scope global | jq -r '.[0].addr_info[0].local | values'

        # Or, if your interface isn't internet facing (and doesn't directly hold your public IP), you can
        # get your external IP address from this free, totally trustworthy* web service.
        # *I have no idea how trustworthy this random webservice is, or if it will even still exist by the time you find this script.
        # _Use at your own risk_
        #CURL_IP_PROTOCOL=$([ "${2}" == "inet6" ] && echo "--ipv6" || echo "--ipv4")
        #curl --silent ${CURL_IP_PROTOCOL} 'https://api.ipify.org?format=json' | jq -r .ip
}

# Updates a CloudFlare DNS record with the given IP address.
# Arg 1: Record name (example.com)
# Arg 2: Record type (A for IPv4, AAAA for IPv6)
# Arg 3: Record value (external IP address)
update_dns() {
        RECORD_NAME="${1}"
        RECORD_TYPE="${2}"
        RECORD_VALUE="${3}"

        # curl note: -f returns non-zero error code for non-OK HTTP response codes. -s stops all stderr output. -S outputs errors when -s is active.

        echo -n "Getting DNS ${RECORD_TYPE} records for ${RECORD_NAME} ..."

        # Get all zones that match the DNS record name
        GET_DNS_LIST_RESULT="$(curl -f -s -S -X GET "${CLOUDFLARE_HOST}/client/v4/zones/${ZONE_ID}/dns_records?type=${RECORD_TYPE}&name=${RECORD_NAME}&order=type&direction=desc&match=all" \
             -H "Content-Type: application/json" \
             -H "Authorization: Bearer ${CLOUDFLARE_API_TOKEN}")"

        [ $? -eq 0 ]  || exit 2

        # jq note: -e returns non-zero error code for null result, -r returns raw output.

        # Grab the first record's ID
        DNS_ID="$(jq -e -r .result[0].id <<< "${GET_DNS_LIST_RESULT}")"

        [ $? -eq 0 ]  || exit 2

        echo "first record ID: ${DNS_ID}"

        echo -n "Getting value for record ID ${DNS_ID} ..."

        # Get the current zone DNS details
        GET_DNS_RESULT="$(curl -f -s -S -X GET "${CLOUDFLARE_HOST}/client/v4/zones/${ZONE_ID}/dns_records/${DNS_ID}" \
             -H "Content-Type: application/json" \
             -H "Authorization: Bearer ${CLOUDFLARE_API_TOKEN}")"

        [ $? -eq 0 ]  || exit 2

        CURRENT_RECORD_VALUE="$(jq -e -r .result.content <<< "${GET_DNS_RESULT}")"

        [ $? -eq 0 ]  || exit 2

        echo "${CURRENT_RECORD_VALUE}"

        # Check if current IP in DNS entry matches our interface IP
        echo "Checking if current DNS value matches external IP address ..."
        echo "Current:  ${CURRENT_RECORD_VALUE}"
        echo "Target :  ${RECORD_VALUE}"

        if [ "${RECORD_VALUE}" = "${CURRENT_RECORD_VALUE}" ]
        then
                echo "Match."
                echo "Not updating record."

                return 0
        else
                echo "Mismatch."
                echo -n "Updating record to ${RECORD_VALUE} ..."
                    # Update the DNS A record to point to the new IP address
                    PUT_DNS_RESULT="$(curl -s -S -X PUT "${CLOUDFLARE_HOST}/client/v4/zones/${ZONE_ID}/dns_records/${DNS_ID}" \
                         -H "Content-Type: application/json" \
                         -H "Authorization: Bearer ${CLOUDFLARE_API_TOKEN}" \
                         --data "{\"type\":\"${RECORD_TYPE}\",\"name\":\"${RECORD_NAME}\",\"content\":\"${RECORD_VALUE}\"}")"

                [ $? -eq 0 ]  || exit 2

                PUT_DNS_SUCCESS="$(jq -e -r .success <<< "${PUT_DNS_RESULT}")"

                [ $? -eq 0 ]  || exit 2

                if [ "${PUT_DNS_SUCCESS}" = "true" ]
                then
                        echo "success."
                        return 1
                else
                        echo "error."
                        echo "${PUT_DNS_RESULT}"
                        return 3
                fi
        fi
}

# =====================
# Start of main script
# =====================

ANY_SUCCESS=0

echo "Checking IPv4 (A record) ..."
EXTERNAL_IPV4="$(get_my_ip ${INTERFACE_NAME} inet)"

if [ -n "${EXTERNAL_IPV4}" ]
then
        echo "External IPv4 address: ${EXTERNAL_IPV4}"

        update_dns "${DNS_ADDRESS}" "A" "${EXTERNAL_IPV4}"
        ret_val=$?
        echo "Return value: ${ret_val}"

        ANY_SUCCESS=1
else
        echo "No external IPv4 address on adapter ${INTERFACE_NAME}"
fi


echo "Checking IPv6 (AAAA record) ..."
EXTERNAL_IPV6="$(get_my_ip ${INTERFACE_NAME} inet6)"

if [ -n "${EXTERNAL_IPV6}" ]
then
        echo "External IPv6 address: ${EXTERNAL_IPV6}"

        update_dns "${DNS_ADDRESS}" "AAAA" "${EXTERNAL_IPV6}"
        ret_val=$?
        echo "Return value: ${ret_val}"

        ANY_SUCCESS=1
else
        echo "No external IPv6 address on adapter ${INTERFACE_NAME}"
fi

if [ "${ANY_SUCCESS}" -ne 1 ]
then
        echo "Adapter ${INTERFACE_NAME} had no external IP addresses, indicating network outage."
        echo "Aborting."
        exit 4
fi

echo "Exiting."
exit $ret_val