CODEWITHSUNDEEP
amazon-web-servicesamazon-ec2amazon-ebs
Mark Kropf
Mark Kropf

Reputation: 101

Attach existing EBS as root device in spot instance request

Is it possible to include an existing, unattached, available EBS volume as the root device in a spot instance request? I'd like to create a setup where the system is up and running when the spot price is met, and after a termination and the spot price comes back into range I can re-request and start an instance right where I left off.

thanks!

Upvotes: 8

Views: 2718

Answers (2)

nebulous
nebulous

Reputation: 766

You can boot with the default spot volume, then pivot_root init to a separate EBS volume.

The EC2 Spotter tool can manage this for you. A snippet from EC2 Spotter's documentation:

The launch script employs user-data to create a boot-time script that attaches the specified EBS volume to /dev/xvdf and then proceeds to do a pivot_root and chroot in order to use it as the main system disk in place of /dev/xvda. When the instance is first created or restarted following an interruption, the /sbin/init on the AMI-based EBS volume (/dev/xvda1) is replaced with a small shell script which performs the magic pivot_root and chroot and then chain-loads the /sbin/init from the specified persistent EBS volume (/dev/xvdf1). An extra reboot is performed when the instance first comes up, to ensure a clean slate. The end-result is a full Linux system running on the persistent volume dev/xvdf mounted as /. The ephemeral disk remains mounted under /old-root and can be unmounted if needed.

Also see this StackOverflow answer: AWS EC2: How to remount previous EBS volume using pivot_root?

Upvotes: 0

Steffen Opel
Steffen Opel

Reputation: 64741

While Overriding the AMI's Block Device Mapping as such is possible, the root device is the exception, unfortunately:

Any instance you launch automatically includes any storage devices in the AMI's block device mapping. You can override that mapping by specifying a block device mapping with the changes that you want at launch time. In your overrides, you can modify the mapping for any of the storage devices except the root device volume. [emphasis mine]

This is also reflected in the respective wizards within the AWS Management Console, which only allow to adjust the root volume size, but not the snapshot it is based upon, see the image within Changing the Root Device Volume to Persist.

Upvotes: 3

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