generate ec2 /etc/hosts

ec2_hosts.rb

#!/usr/bin/env ruby
# coding: utf-8
require 'rubygems'
require 'aws-sdk'

config = {:access_key_id => '',
          :secret_access_key => ''}
AWS.config(config)
ec2 = AWS::EC2.new
ec2 = ec2.regions['ap-northeast-1']

hosts = []
hosts << "127.0.0.1\tlocalhost localhost.localdomain"
ec2.instances.each do |instance|
  next unless instance.status == :running
  tags = instance.tags.to_h
  hosts << "#{instance.private_ip_address}\t#{tags["Name"]}"
end

`cp -p /etc/hosts /etc/hosts.bak`
open("/etc/hosts.new", "w") {|f| f.write hosts.join("\n")+"\n"}
is_same = system("diff -q /etc/hosts.new /etc/hosts > /dev/null 2>/dev/null")
unless is_same
  `cp -p /etc/hosts.new /etc/hosts`
end