Creating, attaching, formatting, mounting, etc. an EBS volume(s) for Ubuntu Linux during CFT stack creation using UserData...

Once the instance has booted can you check that the user data script is created correctly? You can see this via the Console or by logging on to the instance in /var/lib/cloud/instances/i-*.

It looks like there are some '/n' missing from the script above.

If you find the user-data.txt file in /var, copy to /tmp as user-data.sh, chmod 755, then run it by hand to see if there are errors.

If you have only two block devices then the second device is always going to be the last disk device row of the lsblk output. So extract the name by chopping up the output of the command, e.g.

$ SECOND_DISK=/dev/`lsblk -l | grep -w disk | tail -1 | awk '{print $1}'`
$ echo $SECOND_DISK
/dev/sdb

Then use this variable in the commands to create and mount the volume, updating the fstab, and so on.

Well, I'm posting what I went with, though I'm still not happy as there is still no "linkage" between the CFT's Volume Device name ("/dev/xvdb") and the "nvme?n1" disk in the UserData. It's attached so there should be a way to definitively link the two. However, by using the previous two comments, I was able to craft the following UserData bash code to "more often than not" mount the attached EBS volume. Maybe this will help somebody, or get them closer to the actual answer. I left in the "debugging" echo's as they were helpful to show what was being done (as per the first answer). The main problem is that the "lsblk" call is a best guess as to which disk I'll get. And my EBS Root Volume Size "cannot/should not" be the same size as my EBS Data Volume Size:

"UserData": { "Fn::Base64" : { "Fn::Join" : ["", [
    "#!/bin/bash\n",
    "echo Used for debugging - can be deleted at any time >> /build.txt\n",
    "mkdir /data\n",
    "DATA_DISK=$(lsblk -l | grep -w disk | grep ",
    { "Ref" : "DataVolumeSize" },
    " | tail -1 | awk '{print $1}')\n",
    "echo $(lsblk -l) >> /build.txt\n",
    "echo DATA_DISK = $DATA_DISK >> /build.txt\n",
    "mkfs -t ext4 /dev/$DATA_DISK\n",
    "echo $(blkid -o export /dev/$DATA_DISK | grep ^UUID=)       /data  ext4    defaults,nofail 0       2 >> /etc/fstab\n",
    "echo $(blkid -o export /dev/$DATA_DISK | grep ^UUID=)       /data  ext4    defaults,nofail 0       2 >> /build.txt\n",
    "echo blkid= $(blkid -o export /dev/$DATA_DISK)  >> /build.txt\n",
    "mount -a\n",
    "echo $(cat /etc/fstab) >> /build.txt\n",
    ...

P.S. I saw (https://github.com/binxio/ec2-boot-mount-ebs-volume) where someone was using:

    "mkdir /data\n",
    "blkid $(readlink -f /dev/xvdb) || mkfs -t ext4 $(readlink -f /dev/xvdb)\n",
    "e2label $(readlink -f /dev/xvdb) xxx-data\n",
    "sed  -e '/^[\/][^ \t]*[ \t]*\/data[ \t]/d' /etc/fstab\n",
    "grep -q ^LABEL=xxx-data /etc/fstab || echo 'LABEL=xxx-data /data ext4 defaults' >> /etc/fstab\n",
    "grep -q \"^$(readlink -f /dev/xvdb) /data \" /proc/mounts || mount /data\n",

It never worked for me and seemed to always return a blank. BTW, I'm on Ubuntu, so maybe that has something to do with it.