You may want to have a look at this article, I'm guessing it should be relevant to your scenario as well:
https://knowledge.safe.com/articles/60408/fme-desktop-on-amazon-aws-ec2.html
The most important bit:
The fixed license is tied to a specific volume, so if an AMI is created, and then a new instance created from that AMI, it will require a new license. If you need to create multiple instances from an AMI, you will need to use a floating license.
Also important to notice if considering a node-locked license:
Please remember that under the terms of the FME Software License Agreement, you need to configure access to fixed licenses in such a way that the FME Software is only accessible to a single user. If you intend to have multiple users access an FME license, then you should be using a floating license.