update_route53.rb

require 'aws-sdk-core'
require 'yaml'

# class for updating vpc route53
class OptimizelyDNS
  def initialize(options = {})
    @region = options['region'] ||= 'us-east-1'
    @domain = options['domain'] ||= 'default-domain'
    @vpc_id = options['vpc-id'] ||= 'vpc-xxxxxxxx'
    @zones = options['zones']
    @zones ||= { 'A' => 'ZXXXXXXXXXXX', 'PTR' => 'ZXXXXXXXXXXXX', 'CNAME' => 'ZXXXXXXXXXXXX' }
    @route53 = Aws::Route53::Client.new(region: @region)
  end

  def create_record(name, value, record_type)
    puts "Record for #{name} to #{value} of type #{record_type}"
    @route53.change_resource_record_sets(
      hosted_zone_id: @zones[record_type],
      change_batch: {
        changes: [
          {
            action: 'UPSERT',
            resource_record_set: {
              name: name.strip,
              type: record_type,
              ttl: 60,
              resource_records: [{ value: value.strip }],
            },
          },
        ],
      },
    )
  end

  # rubocop:disable MethodLength
  def populate_tags
    Aws.config[:ec2] = { region: @region }
    ec2 = Aws::EC2::Client.new
    filters = [{ name: 'vpc-id', values: [@vpc_id] }]
    resp = ec2.describe_instances(filters: filters)
    resp.reservations.each do |reservation|
      reservation.instances.each do |instance|
        ip = instance.private_ip_address
        raw_name = instance.tags.select { |tag| tag['key'] == 'Name' }.first
        name = raw_name['value'] unless raw_name.nil?
        name ||= ''
        raw_aliases = instance.tags.select { |tag| tag['key'] == 'aliases' }.first
        aliases = raw_aliases['value'].split(',') unless raw_aliases.nil?
        aliases ||= []
        next if name.empty?
        fqdn = get_fqdn(name)
        create_record(fqdn, ip, 'A')
        create_record("#{ip.split('.').reverse.join('.')}.in-addr.arpa", fqdn, 'PTR')
        next if aliases.empty?
        aliases.each do |ali|
          create_record(get_fqdn(ali), fqdn, 'CNAME')
        end
      end
    end
  end

  # just reads a yaml file which is an array of key: value
  def populate_overrides
    overrides = YAML.load_file('overrides.yml')
    overrides.each do |name, ip|
      fqdn = get_fqdn(name)
      create_record(fqdn, ip, 'A')
      create_record("#{ip.split('.').reverse.join('.')}.in-addr.arpa", fqdn, 'PTR')
    end
  end

  private

  def get_fqdn(name)
    "#{name}.#{@region}.#{@domain}"
  end
end

if __FILE__ == $PROGRAM_NAME
  dns = OptimizelyDNS.new
  dns.populate_tags
  dns.populate_overrides
end