HOWTO: updating dynamic DNS on Amazon ... - The Diigo Meta page

• 12 Nov 07
  

  Harjeet Singh

  amazon dns ec2

  •   HOWTO: updating dynamic DNS on Amazon EC2     
           Posted:      Nov 8, 2007 10:55 AM PST                   
                    
    Reply
     
          
      Hey everyone, 
    
    I blogged about this a while ago, but I thought it would help to have it here on the forums as well.  The original post is at  http://spattendesign.com/2007/10/10/updating-dynamic-dns-on-amazon-ec2
    
    The formatting of the code got a little messed up in transition, so it's probably better to go to the blog if you want to cut and paste the code. 
    
    

    basic idea 

    There are two steps to updating your dynamic  DNS . 

     
    1. Get your IP address 
     
    2. Tell your dynamic  DNS  provider the IP address 

    On  EC2 , things are a little different from your standard hosting setup. Here’s how you get dynamic  DNS  working on  EC2 . 

    Getting your IP address 

    See this Amazon article about  getting data about your instance  for more information about instance data. 

    To make a  long  story short, to find out the public IP address of your  EC2  instance, you make a http get request to 

    http://169.254.169.254/latest/meta-data/public-ipv4

    Note that this has to be done from your  EC2  instance. 

    Try it out from the command line. Log-in to your  EC2  instance and type 

    curl  http://169.254.169.254/latest/meta-data/public-ipv4

    From Ruby, it’s just as simple. Cut and paste this into a script, or just run it in irb. 

    require 'open-uri' 
    ip = open(' http://169.254.169.254/latest/meta-data/public-ipv4').read
    

    
    

    Updating your  DNS  with your dynamic  DNS  provider 

    The following instructions assume that you want to use  ez-ipupdate  to update your  DNS . If you don’t want to, or if ez-ipupdate doesn’t support your dynamic  DNS  provider, it should be relatively simple to get it working anyways. 

    For example,  easy-dns  (who I use) just requires logging in and then sending a get request  formatted like this : 

    http://members.easydns.com/dyn/dyndns.php?hostname=example.com&myip=10.0.0.2
    

    Installing ez-ipupdate 

    If you’re running Ubuntu, then install it using  
    

    sudo aptitude install ez-ipupdate  
    

    or  
    

    sudo apt-get install ez-ipupdate.  
    

    On a RedHat installation  
    

    sudo yum install ez-ipupdate. 

    You can also  install from source , of course. 

    When you install it using aptitude or apt-get, it will ask you for some configuration info. This won’t work on  EC2 , so ignore the configuration and use the script below instead. 

    Installing the Ruby script 

    Here’s the script: 
    
    

    
    #!/usr/bin/env ruby 
    require 'open-uri' 
    require 'yaml' 
    
    DYNAMIC_DNS_CONFIG_FILE = '/etc/ez-ipupdate/dynamic_dns.yml' 
    AMAZON_INSTANCE_DATA_ADDRESS = " http://169.254.169.254"
    api = "latest" 
    ip = open(File.join(AMAZON_INSTANCE_DATA_ADDRESS, api, 'meta-data', 'public-ipv4')).read 
    
    dns_config = YAML::load(File.open(DYNAMIC_DNS_CONFIG_FILE)) 
    hosts = dns_config['host'].split(',') 
    hosts.each do |host| 
      puts "updating dynamic dns to ip = #{ip} for host #{host} using dynamic DNS service " + 
           "#{dns_config['service']}" 
      command = "ez-ipupdate --address #{ip} --service-type #{dns_config['service']} " + 
                "--user #{dns_config['username']}:#{dns_config['password']} --host #{host}" 
      puts command 
      system(command) 
    end 
    

    
    

    If you’re running an  ec2-on-rails  instance, place the script in /usr/local/ec2-on-rails/startup-scripts/every-startup/update_dynamic_dns.rb 

    Otherwise, place it somewhere in your path and create a shell script to call it in /etc/init.d. 

    Make sure that both update_dynamic_dns.rb and the init script are executable. 

    The config file 

    Create a file called /etc/ez-ipupdate/dynamic_dns.yml. It should look something like this 

    
    <pre> # service should be one of the services supported by ez-ipupdate.  
    # Possible values: null  ezip  pgpow  dhs  dyndns  dyndns-static  
    #                         dyndns-custom ods tzo easydns easydns-partner  
    #                         gnudip justlinux dyns hn zoneedit heipv6tb 
    # (The above list is from man ez-ipupdate) 
    service: service_type  
    username: username_for_your_dynamic_dns_provider 
    password: password_for_your_dynamic_dns_provider 
    host: example1.com,example2.com			 
    

    
    </pre> 

    To update multiple hosts, put them all on the host entry, separated by commas. 

    Testing and debugging 

    Test out the script: 

     
    • run it: ./update_dynamic_dns.rb. 
     
    • Wait a couple of minutes. 
     
    • ping your domain name from a local machine and make sure that it points at the right IP address. 

    Hopefully that works for you. Let me know if you have any problems, comments or suggestions. 

    Scott

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