setmycfdns - DNS updates for Cloudflare

The scenerio exists where a servers public (external) IP address can change over time. This is especially true with cloud computing.

As instances are stopped or hibernated and then restarted - their public IPs change, leaving public DNS records out of date.

This program can be used to update CloudFlare zone records when a server reboots or returns from hibernation. This gives CloudFlare users the same benifit as a cloud-native DNS solutions.

Limitations

setmycfdns will update existing DNS records - the records must already exist in your CloudFlare zone.

setmycfdns doesn't create or remove records.

This is by design to prevent things from going wrong.

setmycfdns updates A and AAAA DNS records; other records are not supported.

setmycfdns Command Usage and Options

After configuring setmycfdns is simple to use and in most instances does not require any special switchs.

 % setmycfdns 

This will automatically find your public IP address and update the dns zone record based on the fully qualifed domain name (fqdn) of your computer.

In a more complex configuration you can use a different name or multiple ip address.

 % setmycfdns --fqdn first.example.com
 % setmycfdns --fqdn second.example.com -ip 100.100.22.23

A list of all availabe options:

% setmycfdns --help
usage: setmycfdns [-h] [-v] [-ip IP] [-fqdn FQDN] [-q] [-z ZONE] [-6]

Update CloudFlare IP record

optional arguments:
  -h, --help            show this help message and exit
  -v, --version         show program's version number and exit
  -ip IP, --ip IP       set specific IP address to use
  -fqdn FQDN, --fqdn FQDN
                        Fully Qualified Domain Name (rkmbp.sunyocc.edu)
  -q, --query           Query only - no updates are made
  -z ZONE, --zone ZONE  Cloudflare Zone to update (optional)
  -6                    Update AAAA record (default is A record)

setmycfdns gunville 2022 v1

#### Automatic IP detection:

By default `setmyip` automatically detects the public IP address by sending an HTTP request to [icanhazip.com](http://icanhazip.com). This site returns the IP address of the sender.

You can optionally use a different site to autodetect the public ip by setting the environment variable `IPAPIURL` to that URL:
```bash
% IPAPIURL='http://api.ipify.org'
% setmycfdns

When ipv6 is selected with the -6 switch automatic detection uses the ipv6 stack. icanhazip.com works with both ipv4 and ipv6.

If your host has multiple ip addresses or uses a proxy for web requests you will need to provide the ip address to use with the --ip IP command line switch.

% setmycfdns -ip 100.123.4.56
% setmycfdns -6 -ip 2600:1f16:a44:1701:1be3:f8b7:aa51:410b 

Automatic Hostname Determination:

The fqdn of the host is acquired with the Python socket.gethostname() function. (Several solutions were tried, none worked perfect, but this one seems to work best.)

There are some limitations to hostname determination:

• Some systems are not configured to provide the fqdn (web01.example.com) and provide only the short hostname (web01). There is no elegant and simple solution that works on all platforms and configurations.

• In some environments the hostname on the private side (e.g. web01.local) is not the same one used on the public side (web01.example.com).

• Likewise, cloud VPCs by default provide hostnames in a similar fashion (e.g. ip-172-31-84-22.ec2.internal)

In these cases you will be required to provide the full fqdn with the --fqdn FQDN switch.

% setmycfdns --fqdn web01.example.com 

CloudFlare Zone selection:

The cloudflare zone is selected from the FQDN, but can also explicity provided with the --zone ZONE switch.

If the --zone switch is used the the zone does not match the hostname determined above, the fqdn is constructed by appending the zone.

% hostname
server1
% setmycfdns --fqdn server1.example.com        # server1.example.com
% setmycfdns --fqdn server1 --zone example.com # server1.example.com
% setmycfdns --zone eample.com                 # server1.example.com

The above are identical. Note that the fqdn does not have to be 'fully qualified' when the --zone switch is used.

IPv6 Support

Both ipv4 A and ipv6 AAAA DNS records are supported by setmycfdns. To update ipv6 records the -6 switch is used - and required.

% setmycfdns -6

Installation and Configuration

setmycfdns is easily installed using pip

% pip install setmycfdns

CloudFlare API Keys

CloudFlare credentials (API keys) are required. You will need to generate these in your CloudFlare account.

Generally a .cloudflare.cfg file in the users home directory or the current working directory, but there are several options. The format is dictated by the python-cloudflare API library and details can be found here.

Remember to always protect these API keys.

Configuring setmycfdns to Run On Reboots (optional)

The following crontab entry will run setmycfdns each time the server reboots.

@reboot /usr/local/bin/setmycfdns

The actual path depends on where you install setmycfdns

Configuring setmycfdns To Run Post Hibernation (optional)

This may differ some depending on the operating system. This example here works with RedHat flavors.

• Create the following file in /lib/systemd/system-sleep/
• Add these contents of the file
• Set the file to be excutable

% sudo touch /lib/systemd/system-sleep/20_cfdns
% sudo chomd +x /lib/systemd/system-sleep/20_cfdns
% cat > /lib/systemd/system-sleep/20_cfdns <<EOF
#!/usr/bin/env bash
action="$1/$2"
case "$action" in
   pre/hibernate)
   ;;
   post/hibernate)
	/usr/local/bin/setmycfdns
   ;;
esac
>>

The actual path depends on where you install setmycfdns