Some instance types don't support ephemeral storage

[fgreg]

When running sds cloud asg create there should be more intelligence around the block devices being created for the Launch Configuration.

Certain instance types are "EBS Only" and cannot have attached instance storage. The latest Verdi image is configured to map "/dev/sdb" and "/dev/sdc" to ephemeral instance storage devices.

This means that if you select an instance type that is "EBS Only", the instance storage mappings are silently ignored and your worker instances will not work properly.

I think there are a couple of possible solutions to this issue:

1. If the user selects an AMI with ephemeral block device mappings, and then selects an instance type that is EBS Only, warn the user or prevent them from continuing until they select an instance type that supports 2 ephemeral devices.
2. Allow the user to choose to override the ephemeral devices by prompting them something along the lines of "Should EBS be used instead of instance storage?"

[fgreg]

According to @pymonger

The docker-ephemeral-lvm.sh will handle one ephemeral and one EBS instance. Not sure if that’s been ported to the script that @susan Neely uses in the AMI.

https://github.com/hysds/puppet-autoscale/blob/master/templates/docker-ephemeral-lvm.sh

According to @SusanNeely

if sds cloud asg create doesn’t give you options to add ebs, then you’ll need to stick with c3. Gerald’s script is pretty much the same as the one on there in that it needs 3 devices.

Still don't know how to resolve this. When I tried using c5d instances which allow only one ephemeral disk, it didn't work. I needed to use c3 instances which allow two ephemeral disks for it to work correctly.

The problem is that the AMI's define 3 devices:

1. EBS volume used as root disk
2. Ephemeral disk
3. Ephemeral disk

This script handles mounting the devices: https://github.com/hysds/puppet-autoscale/blob/master/templates/docker-ephemeral-lvm.sh but it seems that it requires 3 devices.

The sds cloud asg create function uses the devices defined in the AMI (1 EBS, 2 ephemeral) as part of the launch configuration. So you need to either manually edit the LC after it's created to change from ephemeral to EBS or you need to use an instance type that allows for at least 2 ephemeral devices.