Delete on Termination

I created my web server late last year on an EC2 instance on AWS. While I built the instance with terraform, I didn't set the EBS for the EC2 instance's "Delete on Termination" flag to false. That would mean if I would terminate the instance instead of stop it, that my main EBS volume would just disappear. While that's not that big of a deal because I built the webserver with automation and could easily regenerate it quicky. I didn't necessarily want to lose things like server logs.

I started poking around the console looking for how to switch the flag and I was perplexed how to set it after the fact. I went poking around the web and found there was no way to do it! You have to use the aws ec2 modify-instance-attribute CLI command to change it

Parameters for the CLI

You need two things to be able to use the AWS CLI command

• EC2 instance ID
• Storage device name

The instance ID was easy to get either by using the console or in a roughshod way using the AWS CLI:

$ aws ec2 describe-instances --output yaml | grep Instance
  Instances:
...
    InstanceId: i-04753
    InstanceType: t2.micro
...

The device name is also easy to find in the console by going to the Storage tab, but can also be found via the CLI:

$ aws ec2 describe-instances --output yaml | grep -A 6 BlockDeviceMappings
    BlockDeviceMappings:
    - DeviceName: /dev/xvda
      Ebs:
        AttachTime: '2021-11-28T03:03:28+00:00'
        DeleteOnTermination: true
        Status: attached
        VolumeId: vol-0e40

That would mean our two parameters would be:

• EC2 instance ID: i-04753
• Storage device name: /dev/xvda

Running the CLI

First you need to create a json file that specifies the device name and the DeleteOnTermination flag:

[
  {
    "DeviceName": "/dev/xvda",
    "Ebs": {
      "DeleteOnTermination": false
      }
  }
]

And then you invoke the comand:

aws ec2 modify-instance-attribute --instance-id i-04753 --block-device-mappings file://storage.json

There is no output on a successful change, but you can confirm that the change was made with the same command as above:

$ aws ec2 describe-instances --output yaml | grep -A 6 BlockDeviceMappings
    BlockDeviceMappings:
    - DeviceName: /dev/xvda
      Ebs:
        AttachTime: '2021-11-28T03:03:28+00:00'
        DeleteOnTermination: false
        Status: attached
        VolumeId: vol-0e40

Notice DeleteOnTermination is now set to false.

(HT to Pete Wilcock)