Simple shell script to update specific CloudFlare DNS record with current ip. Useful when you do not have a static IP address, and are hosting your own servers.

cloudflare_ddns.sh

#!/bin/bash

# run this script as a CRON job!

# get the current public ip address
printf "\n"
logger -s "Getting the current public IP address..."
current_ip=`curl -s ipinfo.io/ip`

update_dns_record(){
    # function to update the dns record in cloudflare
    curl -s --request PUT \
         --url https://api.cloudflare.com/client/v4/zones/$CLOUDFLARE_ZONE_ID/dns_records/$CLOUDFLARE_RECORD_ID \
         --header 'Content-Type: application/json' \
         --header "X-Auth-Email: $CLOUDFLARE_EMAIL_ID" \
         --header "X-Auth-Key: $CLOUDFLARE_AUTH_KEY" \
         --data "{
            \"content\": \"$current_ip\",
            \"type\": \"A\",
            \"name\": \"$CLOUDFLARE_RECORD_NAME\",
            \"ttl\": \"$CLOUDFLARE_RECORD_TTL\",
            \"proxied\": $CLOUDFLARE_PROXIED_TRUE_OR_FALSE
         }"
    logger -s "done updating the dns record"
}

# check if `ip.log` file exists (we store the last ip address in this file)
if [ -e ip.log ]
then
    # it exists, so read the last ip address from it
    last_ip=`cat ip.log`

    # compare the current ip address with the last ip address
    if [ "$current_ip" != "$last_ip" ]
    then
        printf "\n"
        logger -s "it has changed, updating dns record..."
        # they are different, so update the DNS record
        update_dns_record

        # save the current ip address to the `ip.log` file
        echo $current_ip > ip.log
        exit 0
    else
        logger -s "ip address has not changed. exiting"
    fi
else
    logger -s "no ip.log file found, creating one"
    echo $current_ip > ip.log
    update_dns_record
    exit 0
fi

# save the current ip address to the `ip.log` file
echo $current_ip > ip.log