Archive for the ‘Compute’ Category

Automating Your Infrastructure with AWS

Demonstration of infrastructure automation with Amazon Web Services.

Behind the Scenes of the Amazon Appstore Test Drive

The beta launch of Test Drive last week on select Android devices has many developers wondering, how does it work?

Jeff Bar, Amazon Web Services Technical Evangelist, has taken the time to walk through the technology behind Test Drive on the AWS blog. Test Drive is hosted on Amazon Elastic Cloud Compute (EC2). The Amazon Appstore team can therefore easily add additional capacity whenever needed and where it makes the most sense with respect to the incoming traffic.

Check out Jeff’s full post on the Amazon Web Services blog.


Update CentOS

There are basically two ways of updating a CentOS machine.. first is by using the GUI and the second, via command line…

Read more here

Install Tomcat 7 or Tomcat 7.0.26 or Tomcat 6 or Tomcat 5 on Ubuntu 11.10 or Ubuntu 11.04 or Ubuntu 10.10 or Ubuntu 10.04 LTS

Uploading Known ssh Host Key in EC2 user-data Script

June 2, 2012 1 comment

I have not tested this personally, but seems to be a correctly put by  . If you try, do let me know if you find any catchs. 🙂

The ssh protocol uses two different keys to keep you secure:

  1. The user ssh key is the one we normally think of. This authenticates us to the remote host, proving that we are who we say we are and allowing us to log in.
  2. The ssh host key gets less attention, but is also important. This authenticates the remote host to our local computer and proves that the ssh session is encrypted so that nobody can be listening in.

Every time you see a prompt like the following, ssh is checking the host key and asking you to make sure that your session is going to be encrypted securely.

The authenticity of host 'ec2-...' can't be established. ECDSA key fingerprint is ca:79:72:ea:23:94:5e:f5:f0:b8:c0:5a:17:8c:6f:a8. Are you sure you want to continue connecting (yes/no)? 

If you answer “yes” without verifying that the remote ssh host key fingerprint is the same, then you are basically saying:

I don’t need this ssh session encrypted. It’s fine for any man-in-the-middle to intercept the communication.

Ouch! (But a lot of people do this.)

Note: If you have a line like the following in your ssh config file, then you are automatically answering “yes” to this prompt for every ssh connection.

# DON'T DO THIS! StrictHostKeyChecking false 

Care about security

Since you do care about security and privacy, you want to verify that you are talking to the right server using encryption and that no man-in-the-middle can intercept your session.

There are a couple approaches you can take to check the fingerprint for a new Amazon EC2 instance. The first is to wait for the console output to be available from the instance, retrieve it, and verify that the ssh host key fingerprint in the console output is the same as the one which is being presented to you in the prompt.

Scott Moser has written a blog post describing how to verify ssh keys on EC2 instances. It’s worth reading so that you understand the principles and the official way to do this.

The rest of this article is going to present a different approach that lets you in to your new instance quickly and securely.

Passing ssh host key to new EC2 instance

Instead of letting the new EC2 instance generate its own ssh host key and waiting for it to communicate the fingerprint through the EC2 console output, we can generate the new ssh host key on our local system and pass it to the new instance.

Using this approach, we already know the public side of the ssh key so we don’t have to wait for it to become available through the console (which can take minutes).

Generate a new ssh host key for the new EC2 instance.

tmpdir=$(mktemp -d /tmp/ssh-host-key.XXXXXX) keyfile=$tmpdir/ssh_host_ecdsa_key ssh-keygen -q -t ecdsa -N "" -C "" -f $keyfile 

Create the user-data script that will set the ssh host key.

userdatafile=$tmpdir/set-ssh-host-key.user-data cat <<EOF >$userdatafile #!/bin/bash -xeu cat <<EOKEY >/etc/ssh/ssh_host_ecdsa_key $(cat $keyfile) EOKEY cat <<EOKEY >/etc/ssh/ $(cat $ EOKEY EOF 

Run an EC2 instance, say Ubuntu 11.10 Oneiric, passing in the user-data script. Make a note of the new instance id.

ec2-run-instances --key $USER --user-data-file $userdatafile ami-4dad7424 instanceid=i-... 

Wait for the instance to get a public DNS name and make a note of it.

ec2-describe-instances $instanceid 

Add new public ssh host key to our local ssh known_hosts after removing any leftover key (e.g., from previous EC2 instance at same IP address).

knownhosts=$HOME/.ssh/known_hosts ssh-keygen -R $host -f $knownhosts ssh-keygen -R $(dig +short $host) -f $knownhosts ( echo -n "$host "; cat $ echo -n "$(dig +short $host) "; cat $ ) >> $knownhosts 

When the instance starts running and the user-data script has executed, you can ssh in to the server without being prompted to verify the fingerprint

ssh ubuntu@$host 

Don’t forget to clean up and to terminate your test instance.

rm -rf $tmpdir ec2-terminate-instances $instanceid 


There is one big drawback in the above sample implementation of this approach. We have placed secret information (the private ssh host key) into the EC2 user-data, which I generally recommend against.

Any user who can log in to the instance or who can cause the instance to request a URL and get the output, can retrieve the user-data. You might think this is unlikely to happen, but I’d rather avoid or minimize unnecessary risk.

In a production implementation of this approach, I would take steps like the following:

  1. Upload the new ssh host key to S3 in a private object.
  2. Generate an authenticated URL to the S3 object and have that URL expire in, say, 10 minutes.
  3. In the user-data script, download the ssh host key with the authenticated, expiring S3 URL.

Now, there is a short window of exposure and you don’t have to worry about protecting the user-data after the URL has expired.


AWS – Migrate Linux AMI (EBS) using CloudyScripts

In a typical Amazon Web Services(AWS) Environment, Amazon Machine Images (AMIs) are strictly available in a certain region only. These AMIs cannot be moved from one region to another. Though the AMIs are shared within different Availability Zones of the same region. For this purpose, you can use a third party tool called as CloudyScripts.

CloudyScripts is a collection of tools to help you programming Infrastructure Clouds. The web-based tool is self explanatory and regularly updated. In case you find any bug, do not hesitate to email the owners right away.

Goto the CloudyScripts Copy AMI to different region tool.

AMI should be EBS-backed Linux AMI only. The AWS Access Key and Secret Key can be found at the Security Credentials page of your AWS Account. This information is unique to your account and can be misused. DO NOT share these details with anyone.

The key provided should be generated in the source and target region before using the tool. Provide the .pem key files.

AWS discourages use of “root” user for login into AWS EC2 Instances.

You may use different ssh users like, “ec2-user” for AWS Linux Instances or “ubuntu” user for Ubuntu instances.

Output will be displayed as:

Verify that the AMI is registered in the destination as Private to you i.e.owner.

If you opt to receive mail of the status, enter your email id in the status window.

The mail will be received as:

AWS EBS-Backed Instance Backup &Restore

Starting with the 2009-10-31 API, Amazon Web Services (AWS) has a new type of Amazon Machine Image(AMI) that stores its root device as an Amazon Elastic Block Store(EBS) volume. They refer to these AMIs as Amazon EBS-backed. When an instance of this type of AMI launches, an Amazon EBS volume is created from the associated snapshot, and that volume becomes the root device. You can create an AMI that uses an Amazon EBS volume as its root device with Windows or Linux/UNIX operating systems.These instances can be easily backed-up. You can modify the original instance to suit your particular needs and then save it as an EBS-backed AMI. Hence, if in future you need the the modified version of instance, you can simply launch multiple new instances from the backed-up AMI and are ready to-go.

Following are the steps to be performed for backup/restoring of AWS EBS instance into/from an AWS AMI. Also brief steps for deletion of AMI backup are noted for reference.

EBS-instance to EBS-backed AMI

  • Go to AWS Management Console and in the My Instances Pane, select the instance which has to be backed up.
  • Right click the instance and select option Create Image (EBS AMI).
  • In the Create Image dialog box, give proper AMI Name and Description. Click on Create This Image button.
  • The image creation will be in progress. This will take sometime depending upon the number & size of volumes attached to the instance. Click on View pending image link. It will take you to the AMIs pane.
  • The AMI will be in pending state. It is important to note that this AMI is private to the account and not available for AWS public use.
  • If you select Snapshots from the Navigation Pane, then you can see that EBS volumes attached to the instance will be backed up as too.
  • Once the backup is done, the AMI will be in available state.


Restore from backup AMI into instance

In case, the running instance needs to be restored, use the latest backup AMI. To launch an instance from this AMI, right-click the AMI and select Launch Instance option. The Launch Instance Wizard will be displayed, perform the usual configurations and a new instance will be created containing all the data & configurations done before backup.


Delete AMI & Snapshots:

  • To delete any AMI, Right-click it and select De-register AMI.
  • Remember, deleting AMI doesn’t delete the EBS volume snapshots. Click on Snapshots from Navigation pane, search & select the snapshot(s) to be deleted. Right-click on the snapshot(s) and select delete snapshot option.