Create, partiton and format EBS volume in a script for AWS EBS

launchconfig.tf

resource "aws_launch_configuration" "test" {
  name_prefix = "lc-test-"

  image_id                    = "${data.aws_ami.ubuntu.image_id}"
  instance_type               = "t2.small"
  security_groups             = ["${aws_security_group.test.id}"]
  associate_public_ip_address = false
  key_name                    = "${var.bastion_keypair_name}"  /* bastion == bounce host since there is no public ip */
  user_data                   = "${data.template_file.user_data.rendered}"
  iam_instance_profile        = "${aws_iam_instance_profile.test.arn}"
  ebs_optimized               = true

  ebs_block_device {
    device_name           = "/dev/sdf"
    volume_type           = "standard"
    volume_size           = "${var.storage_size}" /* number in GB */
    delete_on_termination = false
    encrypted             = true  /* no excuses.  though, you should manage your keys as well */
  }

  lifecycle {
    create_before_destroy = true  /* bad things happen if you don't do this */
  }
}

user_data.sh

#!/bin/bash
# This is your 'template' in its rendered state, comments for unrendered

# In your launch configuration, attach a device with name /dev/sdf
# In terraform

# Question - how do i know the device is ready?
# Answer: web calls
INSTANCE_ID=`curl http://169.254.169.254/latest/meta-data/instance-id/`
export AWS_DEFAULT_REGION=${region}
aws ec2 wait volume-in-use --filters "Name=attachment.instance-id,Values=$INSTANCE_ID,Name=attachment.device,Values=/dev/sdf,Name=attachment.status,Values=attached"

# This is hard coded, because I'm too lazy to on the fly translate the /dev/sdaf into /dev/xvdf
# But it would be something like `echo ${device_name} | sed -- "s/sda/xvd/g"`
# < <( ... ) is process substitution.  Kinda like a backwards pipe: 
# https://stackoverflow.com/questions/2443085/what-does-cmd-args-mean-in-the-shell
sudo sfdisk /dev/xvdf < <(echo "start=2048, type=83")

sudo mkfs.ext4 /dev/xvdf1
BLOCK_ID=`blkid /dev/xvdf1 -s UUID -o value`

# Setup your mount points.  For example, (read man hier !), to store cassandra data in /var/opt/
echo "UUID=$BLOCK_ID  /var/opt/cassandra  ext4  default,nofail,nobootwait 0 2" >> /etc/fstab
sudo mount -a

# do rest of setup stuff