Issue Report

Feature Request

Environment

AWS CoreOS 1688.5.3 HVM on m5.* or c5.* instances

Desired Feature

Add udev symlink rules to map NVMe devices to traditional xvd[a-z] device names.

Other Information

With the newer m5 and c5 instances, EBS volumes show up as NVMe devices. AWS Linux provides built-in udev rules that symlink the NVMe devices to their equivalent /dev/sd[a-z] naming. This keeps things consistent with the older naming rules and matches what is configured in EBS block device mappings provided when launching the instance.

It would be great if CoreOS could provide similar rules. This would allow systemd mounts to work across all EC2 instance types without special hacks or relying on fixed device names. AWS Linux handles this with the help of a python script named ebsnvme-id that read EBS information from the NVMe device. I realize python is not installed on CoreOS, but the script could be rewritten to provide the basic functionality needed for udev renaming.

More information can be found here:
kubernetes-retired/kube-aws#1048
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/nvme-ebs-volumes.html

An example udev rule without using the python script can be found here: https://github.com/oogali/ebs-automatic-nvme-mapping

I can't seem to find the python script publicly, but it's available on the Amazon Linux AMI and is licensed under the Apache 2.0 license. I've copied the current udev rules and scripts from the Amazon Linux AMI here: https://gist.github.com/jalaziz/c22c8464cb602bc2b8d0a339b013a9c4

One thing I've noticed (and has been mentioned elsewhere) is that the device name in the vendor-specific name is different depending on when and how the volume is mounted. For example, it seems that volumes mounted pre-boot do not have the /dev/ prefix in the vendor info, while volumes mounted after have the /dev/ prefix. Also, it appears that the device is not renamed to the xvd naming convention automatically.