How to Communicate Among Instances using Amazon EC2

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Nimantha de Silva, Freelance Technical Writer will guide you through on how to communicate among instances using Amazon EC2. This will be done in a step by step manner, so that the user can does not need any extensive knowledge on how to deploy the following.


Submitted By: nimantha
AWS Products Used: Amazon EC2
License: Other
Created On: May 3, 2010 8:13 AM GMT
Last Updated: August 16, 2010 5:26 PM GMT

This is one of the simplest but the coolest work I tried using Amazon EC2.During the implementation process, the major challenge I had to face was to communicate between instances. For this to work, 1st i had to make sure that my application has the capability to recall "[b]ssh[/b]" and "[b]scp[/b]"among the nodes, which in most scenarios do happen automatically. This was fun but was hard as I mentioned at the beginning itself, because in EC2 if you want to connect to an instance you have to define the key-pair, which is not possible for my application. So I had to follow an alternative method and these are the steps of how I got it fixed:

  • First step is to run an instance with the your operating system (in my case I was using Fedora 8 and selected it)
  • Once it is done and ready to run the application, you have to select the key-pair and the security group.
  • Next step is to generate the SSH key, you can do that by using the following command (Remember : Do not enter a passphrase)
  • ssh-keygen -t rsa
  • Next is to go and edit the [b]~/.ssh/authorized_keys[/b]. For that copy and paste the content of [b].ssh/[/b]
  • Now open the [b]~/.ssh/authorized_keys[/b], and change the tail as "[b]root@domU[/b]" , (Basically to remove root@ec2-.. with the new one)
  • Next step is to edit the "[b]~/.ssh/know_hosts[/b]" file and add the following command to it.
  • * ssh-rsa Asasdas...
  • (Asasdas.... = content of
Now its done and all set (unless you need to install some other packages).

  • Next step is to bundle the image and register it with EC2 and S3.
  • After doing that, try running more than one instances.
  • Now if you try to do "[b]ssh[/b]" among these you will figure out that you do not need to enter the password or even you do not need to specify the key-pairs for it.
[b]Author: Nimantha de Silva [][/b]
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