cloud-init: run in bootcmd. image is expected to have ephemeral devices letters b-e.

mkfs_data.sh

#!/bin/bash
set -e

if lvs ephemeral/data > /dev/null 2>&1; then
  echo 'lvm already created; exiting'
  exit 0
fi

if ls /dev/xvd* > /dev/null 2>&1; then map='xvd'; fi
if ls /dev/sd* > /dev/null 2>&1; then map='sd'; fi
if [ -z $map ]; then echo 'no drives found; exiting'; exit 0; fi

if ! ls /dev/$map[b-e] > /dev/null 2>&1; then
  echo 'no ephemeral drives found; exiting'
  exit 0
fi

pvcreate /dev/$map[b-e]
vgcreate ephemeral /dev/$map[b-e]
lvcreate ephemeral -n data -l 90%FREE
mkfs.ext4 /dev/ephemeral/data
echo '/dev/ephemeral/data /data ext4 defaults,nofail,comment=cloudconfig 0 0' >> /etc/fstab
! [ -d /data ] && mkdir /data
mount /data