How to use cloud-init to mount block storage that's already formatted and ready to mount?

I’m using Ubuntu 16.04 on a droplet using Terraform. I have an existing volume that’s already been formatted that I would like to mount to /home so I can persist my user directory between applications from terraform.

Unfortunately, while /etc/cloud/cloud.cfg lists mounts in it’s cloud_init_modules no entry is ever written to /etc/fstab.

This is in my userdata:

#cloud-config
mounts:
  - - '/dev/disk/by-id/scsi-0DO_Volume_volume-name-here-part1'
    - '/home'
    - 'ext4'
    - 'defaults,nofail,discard'
    - '0'
    - '2'
packages:
  - zsh
  - git
  - ufw
users:
  - name: demo
    groups: sudo
    shell: /bin/zsh
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    ssh-authorized-keys:
      - 'ssh-rsa <snip>'
runcmd:
  # Secure SSHD
  - [ sed, -i, -e, 's/^PermitRootLogin yes/PermitRootLogin no/', '/etc/ssh/sshd_config' ]
  - [ service, sshd, restart]
  - [ rm, -f, /root/.ssh/authorized_keys ]
  # Secure UFW
  - ufw default deny incoming
  - ufw default allow outgoing
  - ufw allow ssh
  - ufw enable

If I run this command as root, cloud-init -d single -n mounts, the entry is written to /etc/fstab and /home is mounted. Then I need to run mkhomedir_helper demo to recreate my home directory.

How can I get the mounts module to run automatically? The cloud-config docs are…less than ideal and don’t really explain anything in the examples except how to structure the mounts hash.