It is hard to maintain a regular internet uptime with home connections. 1/2 router re-connections per week can be fairly common. When that happens, the public IP changes with most ISPs. This can be annoying if you want access your computer remotely (possibly to SSH home). Dynamic DNS is a solution that exists to solve just that.

I maintain DNS entries for my domain at Clouflare. The latest version of ddclient supports Cloudflare API, which works well with my ArchLinux box. But ddclient bundled with Raspbian, is yet to get that update. Cloudflare’s API is fairly straight forward, so I decided to use a curl/systemd based solution on my RaspberryPi.

Configuration information

If you too want to set Dynamic DNS with Cloudflare, you need to acquire some configuration information first:

Cloudflare configuration details

• DNS Zone
  You can get it by visiting the overview page of Cloudflare dashboard (called Zone ID): https://www.cloudflare.com/a/overview/

• Auth Email: This is your cloudflare account email.

• Auth Key: This is your Global API Key under Cloudflare account settings: https://www.cloudflare.com/a/account/my-account

• IDENTIFIER
  To get the identifier, you need to first set an A record for the subdomain you want to manage with Dynamic DNS. Then, plug in the subdomain in this curl query to obtain the identifier:

  curl "https://api.cloudflare.com/client/v4/zones/<your-dns-zone>/dns_records?name=<subdomain>.<your-domain>" \
       --silent -X GET \
       -H "X-Auth-Email: <cloudflare-auth-email>" \
       -H "X-Auth-Key: <cloudflare-auth-key>" \
       -H "Content-Type: application/json" 
  

IP Address

I use dig with OpenDNS to get the current public IP and https://www.ipify.org/ as a fallback if dig isn’t installed. Using dig is faster though and you can install it via dnsutils (available as an official package on most systems).

The script

All the above information can now be plugged in this bash script to update the DNS entry on Cloudflare. I placed it at /usr/local/bin/cloudflare-ddns.sh

#/usr/bin/env sh

# Get the Zone ID from: https://www.cloudflare.com/a/overview/<your-domain>
DNS_ZONE=<your-dns-zone>

# Get the existing identifier for DNS entry:
# https://api.cloudflare.com/#dns-records-for-a-zone-list-dns-records
IDENTIFIER=<your-domain-dns-entry-identifier>

# Get these from: https://www.cloudflare.com/a/account/my-account
AUTH_EMAIL=<cloudflare-auth-email>
AUTH_KEY=<cloudflare-auth-key>

# Desired domain name
DOMAIN_NAME="<subdomain>.<your-domain>"

# Get previous IP address
_PREV_IP_FILE="/tmp/public-ip.txt"
_PREV_IP=$(cat $_PREV_IP_FILE &> /dev/null)

# Install `dig` via `dnsutils` for faster IP lookup.
command -v dig &> /dev/null && {
    _IP=$(dig +short myip.opendns.com @resolver1.opendns.com)
} || {
    _IP=$(curl --silent https://api.ipify.org)
} || {
    exit 1
}

# If new/previous IPs match, no need for an update.
if [ "$_IP" = "$_PREV_IP" ]; then
    exit 0
fi

_UPDATE=$(cat <<EOF
{ "type": "A",
  "name": "$DOMAIN_NAME",
  "content": "$_IP",
  "ttl": 120,
  "proxied": false }
EOF
)

curl "https://api.cloudflare.com/client/v4/zones/$DNS_ZONE/dns_records/$IDENTIFIER" \
     --silent \
     -X PUT \
     -H "Content-Type: application/json" \
     -H "X-Auth-Email: $AUTH_EMAIL" \
     -H "X-Auth-Key: $AUTH_KEY" \
     -d "$_UPDATE" > /tmp/cloudflare-ddns-update.json && \
     echo $_IP > $_PREV_IP_FILE

Try running cloudflare-ddns.sh to see if DNS records get updated on Cloudflare. For debugging purposes, I store the Cloudflare response at /tmp/cloudflare-ddns-update.json.

Systemd

We’ll automate this execution by writing a systemd service and a timer.

Configuring the service

My systemd service unit looks like this: /etc/systemd/system/cloudflare-ddns.service

[Unit]
Description=Update DNS entry for this host to current IP

[Service]
Type=oneshot
ExecStart=/bin/sh /usr/local/bin/cloudflare-ddns.sh

Test the service by running:

sudo systemctl start cloudflare-ddns.service
# Check the results:
sudo journalctl -u cloudflare-ddns

Setting up a timer

Set up a timer, so that DNS update is attempted every 2 minutes: /etc/systemd/system/cloudflare-ddns.timer

[Unit]
Description=Update DNS entry in cloudflare every 2 minutes

[Timer]
OnBootSec=1min
OnCalendar=*:0/2
Unit=cloudflare-ddns.service

[Install]
WantedBy=basic.target

To enable the timer, run:

sudo systemctl enable cloudflare-ddns.timer

And that’s it, now the system’s IP will be kept up to date (within 2 minutes) for remote access.

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