ec2 のインスタンス名をホストファイルに登録する

update_ec2_hosts.rb

#!/usr/bin/env ruby
require 'json'
require "optparse"

options = { update: true }
argv = []

OptionParser.new do |opt|
  opt.on("--dry-run") { |v| options[:update] = false }
  argv = opt.parse!(ARGV)
end


def update_ec2_hosts account, options
  res = `aws ec2 describe-instances --filters Name=instance-state-name,Values=running`

  return if JSON.parse(res)['Reservations'].empty?
  instances = JSON.parse(res)['Reservations'].map{ |r| r['Instances'][0] }

  str_begin = "### #{account} BEGIN"
  str_end   = "### #{account} END"

  hosts = instances.select {|i|
    i.has_key?('Tags') and i.has_key?('State') and i['State']['Name'] == 'running' and i['Tags'].select { |t| t['Key'] == 'Name' }.size === 1
  }.map {|i|
    name = i['Tags'].select { |t| t['Key'] == 'Name' }.first['Value']
    "#{i['PublicIpAddress']}\t#{account}.#{name}"
  }

  puts hosts

  return unless options[:update]

  `sed -i.bak -e "/#{str_begin}/,/#{str_end}/d" /etc/hosts`

  open('/etc/hosts', 'a') do |f|
    f.puts str_begin
    f.puts hosts
    f.puts str_end
  end
end

account = argv.first || 'ec2'
update_ec2_hosts account, options