Quick Route53 DynDNS script. Ruby translation of https://willwarren.com/2014/07/03/roll-dynamic-dns-service-using-amazon-route53/

dyndns.rb

#!/usr/bin/env ruby

require 'time'
require 'logger'
require 'aws-sdk'

AWS_REGION = "us-east-1"
AWS_KEY_ID = ""
AWS_SECRET_KEY = ""

HOSTED_ZONE_ID = ""
RESOURCE_NAME = "blah.example.com."

LAST_IP_FILE = "./.dyndns_last_ip"
LOG_FILE = "/var/log/dyndns.log"
LOG_LEVEL = Logger::WARN

log_file_path = File.expand_path(LOG_FILE, File.dirname(__FILE__))

begin
  logger = Logger.new(log_file_path)
  logger.level = LOG_LEVEL
rescue Errno::ENOENT
  File.open(log_file_path, "w").close
  retry
end

begin
  path = File.expand_path(LAST_IP_FILE, File.dirname(__FILE__))
  last_ip = File.read(path).chomp
rescue Errno::ENOENT
  logger.warn "last ip file not found: #{path}"
  last_ip = nil
end

current_ip = `dig +short myip.opendns.com @resolver1.opendns.com`.chomp

unless $? == 0
  logger.fatal "dig exited with error code: #{$?}"
  logger.close
  exit 1
end

unless current_ip =~ /^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$/
  logger.fatal "invalid ip: '#{current_ip}'"
  logger.close
  exit 2
end

if last_ip == current_ip
  logger.info "ip hasn't changed from #{last_ip}, exiting"
  logger.close
  exit
end

route53 = Aws::Route53::Client.new(
  region: AWS_REGION,
  access_key_id: AWS_KEY_ID,
  secret_access_key: AWS_SECRET_KEY
)

begin
  route53.change_resource_record_sets({
    hosted_zone_id: HOSTED_ZONE_ID,
    change_batch: {
      comment: "dyndns script change at #{Time.now.iso8601}",
      changes: [
        {
          action: "UPSERT",
          resource_record_set: {
            name: RESOURCE_NAME,
            type: "A",
            ttl: 60,
            resource_records: [
              {
                value: current_ip,
              },
            ],
          },
        },
      ],
    },
  })
rescue Aws::Errors::ServiceError => e
  logger.fatal "aws failed with error: #{e.class}: #{e.message}"
  logger.close
  exit 3
end

File.write(path, current_ip)
logger.info "changed ip from #{last_ip} to #{current_ip}"
logger.close

requires gem aws-sdk ~> 2

I recommend creating a IAM user that only has permission route53:ChangeResourceRecordSets