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aws-dyndns

A minimalistic approach to Dynamic DNS using AWS Route 53.

Motivation

This whole solution was done in just a few hours, because it offloads most of the work to other SaaS/PaaS:

  • you need a hosted DNS zone under AWS Route 53
  • interaction with the AWS API is done using their official command-line CLI
  • authentication is done by AWS using a restricted IAM user
  • your remote IP address is discovered using the free "ipify" service

Communication is done entirely via HTTPS, and does not require "root" on the Linux machine.

Prerequisites

This script depends on the AWS CLI, dig, and Curl. On a Debian/Ubuntu machine, use the following command to install them:

sudo apt-get install awscli dnsutils curl

Installation

Besides already having a hosted DNS zone under AWS Route 53, you need to set up the following in the AWS IAM console:

  • Create a user.
  • Write down the "Access Key ID" and "Secret Access Key" credentials.
  • Click on the newly created user to edit its properties. Click Inline Policies to create one. Use the Policy Generator:
    • Effect: Allow
    • AWS Service: Amazon Route 53
    • Actions: select only "ChangeResourceRecordSets"
    • Amazon Resource Name (ARN): arn:aws:route53:::hostedzone/%ID%
      • You can get the ID of your hosted zone from the list of the "Hosted zones" in your AWS Route 53 service.
      • Example: arn:aws:route53:::hostedzone/Z148QEXAMPLE8V
  • Click Next. The final Policy Document would look something like:
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt1456599587000",
            "Effect": "Allow",
            "Action": [
                "route53:ChangeResourceRecordSets"
            ],
            "Resource": [
                "arn:aws:route53:::hostedzone/Z148QEXAMPLE8V"
            ]
        }
    ]
}
  • Click "Apply Policy".

On the Linux machine, you need to do the following:

  • Install the Prerequisites packages (described above).
  • Configure the AWS login credentials by executing:
aws configure
  • Run the script manually; here is an example:
./aws-dyndns test.example.com 5 Z148QEXAMPLE8V 30

You should ensure that this script runs all the time. The easiest way would be to add the following to your /etc/rc.local file, which will start the script in background on system boot:

/usr/bin/sudo -u $YOUR_USER \
        /home/$YOUR_USER/$PATH_TO_SCRIPT/aws-dyndns \
        test.example.com 5 Z148QEXAMPLE8V 30 2>&1 | logger -t awsdyndns --id=$$ &

Installing aws-dyndns as a systemd service

Running aws-dyndns as a systemd service will start the service boot, manage logging, execute with the least possible permissions, and relaunch on crash.

# These commands are relative to the project root. Change directories to get there.
cd aws-dyndns

# This will launch the default editor, so you can set a configuration.
# Because this will run as the unprivileged nobody/nogroup user/group we need to pass the AWS credentials.
editor systemd/aws-dyndns.conf

# The configuration file needs to be readable by root, but we can give it very restrictive permissions to protect our AWS key.
sudo chown root:root aws-dyndns systemd/aws-dyndns.service systemd/aws-dyndns.conf 
sudo chmod 600 systemd/aws-dyndns.conf

# Install the executable, configuration, and service
sudo mv aws-dyndns /usr/local/sbin
sudo mv systemd/aws-dyndns.conf /etc/
sudo mv systemd/aws-dyndns.service /etc/systemd/system

# Reload systemd and then start the service.
sudo systemctl daemon-reload
sudo systemctl start aws-dyndns

# Check the log to make sure everything started as expected.
tail -n 20 /var/log/syslog

Sample log output

[Sun Feb 28 11:06:44 EET 2016]: No IP change detected: 190.204.20.169
[Sun Feb 28 11:07:16 EET 2016]: Updating IP to: 181.251.13.59 (test.example.com); OLD=190.204.20.169
{
    "ChangeInfo": {
        "Comment": "DynDNS update",
        "Status": "PENDING",
        "Id": "/change/C459FZQZ7R9H4",
        "SubmittedAt": "2016-02-28T09:07:18.616Z"
    }
}
[Sun Feb 28 11:07:18 EET 2016]: Done. Updated IP to: 181.251.13.59 (test.example.com)
[Sun Feb 28 11:07:50 EET 2016]: No IP change detected: 181.251.13.59
...
curl: (28) Resolving timed out after 5517 milliseconds
[Sun Feb 28 11:47:09 EET 2016]: Invalid NEW_IP: 
[Sun Feb 28 11:47:40 EET 2016]: No IP change detected: 181.251.13.59
...

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