All nodes in EC2 can fetch their Instance Identity Documents. This returns an AWS-signed block containing data about the instance that requested it. This data is only available to the instance that fetched it, so if it turns around and presents it to some other service you can be confident it originated from the machine in question.
This is useful for secrets-enrollment processes where you want a node to be able to attest to its own identity in a secure fashion. Your enrollment mechanism can ensure that the node is ‘young’ enough to be making the request, and that the enrollment has never occured before. Your enrollment tool can also look up other data about the instance (autoscale group, CloudFormation stack, etc) to determine what privileges it should be granted.
In this manner you can pivot on the security features AWS offers for identifying a particular node to another tool.