Formatting and mounting persistent disks on GCE with Ansible
I was working on using Ansible to format and mount persistent disks on Google Compute Engine (GCE). The question I had was how to determine if the disk needed to be formatted and mounted.
In this case the solution turned out to be simple since there are sym-links to
/dev/disk/by-id/. The latter folder contains the
disk-name assigned to the disk when it’s attached to the GCE instance. The only caveat is that
google- is prefixed to the name.
With that knowledge, the same steps provided in the Google Cloud Platform (GCP) documentation can be used: https://cloud.google.com/compute/docs/disks/add-persistent-disk. The only change is replacing the paths.
After testing those commands manually, I wrote a simple Ansible role to automate the process.
- name: Check if disk exists shell: "file -sL /dev/disk/by-id/google-" register: disk_exists - name: Format disk shell: "mkfs.ext4 -m 0 -F -E lazy_itable_init=0,lazy_journal_init=0,discard /dev/disk/by-id/google-" when: "'UUID=' not in disk_exists.stdout" - name: Create mount directory file: dest: "/mnt/disks/" state: directory owner: root group: root mode: 0755 - name: Mount drive mount: path: "/mnt/disks/" src: "/dev/disk/by-id/google-" fstype: ext4 opts: discard,defaults state: mounted
This role will only format and mount a single disk specified via the
disk_name variable. I felt this was the safest way to approach things. In my use case I didn’t have many disks to attach to my instances.
The first step in this role is to check if the disk is formatted. This could be more robust if I handled the case where the disk was not attached.
Next, if the disk exists, we’ll format the disk if it does not contain
UUID= which appears in
file -sL when the disk is formatted.
Finally, the built-in Ansible
mount modules can be used for creating a mount directory and then mounting the disk to that location.