Noob question about KMS and EC2

Question

Why my EC2 instances are able to start, using an encrypted root volume (with a CMK), if the EC2 instance does not have any role attached?

- I created an EC2 instance, and stop it
- I created a snapshot from the root volume
- Then I created a new encrypted volume from the snapshot, using a CMK which only allows one specific role for cryptographic operations
- Then I detached the unencrypted volume, and attached the encrypted volume as root for the EC2 instance (xvda)
- After starting again the EC2, everything worked fine, why?

Thanks.

Answer

From [How EBS encryption works when the snapshot is encrypted](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSEncryption.html#how-ebs-encryption-works)

```
When you attach the encrypted volume to an instance, Amazon EC2 sends a CreateGrant request to AWS KMS so that it can decrypt the data key.
```

Answer

You are invoking "StartInstances" API with your IAM user or Role which has enough privileges on KMS which is the reason EC2 instance is starting all the time with encrypted volumes. If your user ID or Role does not have access to KMS then Ec2 instance will not launch and Ec2 running status will change from Pending to Stopped state every time after  starting instance.

Noob question about KMS and EC2

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