setmy53dns 24.12.25

Updates a hosts Route53 record for use on reboot or waken from hibernation

setmy53dns - DNS updates for Route53

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

This program can be used to update Route53 public zone records automatically when a server reboots or returns from hibernation, and can be used both in the cloud and on-prem if needed.

Limitations

setmy53dns will update existing DNS records - the records must already exist in your Route53 zone.

setmy53dns doesn't create or remove records.

This is by design to prevent things from going wrong.

setmy53dns updates A and AAAA DNS records; other records are not supported.

setmy53dns Command Usage and Options

After configuring setmy53dns is simple to use and in most instances does not require any special switchs.

 % setmy53dns 

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.

 % setmy53dns --fqdn first.example.com
 % setmy53dns --fqdn second.example.com -ip 100.100.22.23

A list of all availabe options:

% setmy53dns --help
usage: setmy53dns [-h] [-v] [-ip IP] [-fqdn FQDN] [-q] [-z ZONE] [-6]

Update Route53 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  Route53 Zone to update (optional)
  -6                    Update AAAA record (default is A record)

setmy53dns gunville 2025 v2

Automatic IP detection:

By default setmyip automatically detects the public IP address by sending an HTTP request to ipv4.icanhazip.com. This site returns the IPv4 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:

% IPAPIURL='http://api.ipify.org'
% setmy53dns

When ipv6 is selected with the -6 switch automatic detection uses the ipv6 stack. ipv6.icanhazip.com. This can be overriden with the environment variable IPV6APIURL.

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.

% setmy53dns --ip 100.123.4.56
% setmy53dns -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.

% setmy53dns --fqdn web01.example.com 

Route53 Zone selection:

The Route53 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
% setmy53dns --fqdn server1.example.com        # server1.example.com
% setmy53dns --fqdn server1 --zone example.com # server1.example.com
% setmy53dns --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 setmy53dns. To update ipv6 records the -6 switch is used - and required.

% setmy53dns -6

Installation and Configuration

setmy53dns is easily installed using pip

% pip install setmy53dns

AWS Credentials

• The AWS user or role used for setmy53dns must have these permissions to make updates:
  • route53:ListHostedZones to Route53
  • route:53ChangeResourceRecordSets and route53:ListResourceRecordSets to the zones that will be updated.
  • with IAM the smallest resource scope to assign privileges is a zone.
• For EC2 instances privileges can be granted with a role attached to an EC2 instance.
• Otherwise they are provided with an AWS credentials file containing API keys to an account that has these privileges granted. (though environment variables can be used.)

Configuring setmy53dns to Run On Reboots (optional)

The following crontab entry will run setmy53dns each time the server reboots.

@reboot /usr/local/bin/setmy53dns

The actual path depends on where you install setmy53dns

Configuring setmy53dns 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/setmy53dns
   ;;
esac
EOF

The actual path depends on where you install setmy53dns