Automate GCP persistent disk initialization

Question

Are there any scripts that automate persistent disks formatting and attaching to the Google Cloud VM instance, instead of doing formatting & mounting steps?

The persistent disk is created with Terraform, which also creates a VM and attaches the disk to it with the attached_disk command.

I am hoping to run a simple script on the VM instance start that would:

check if the attached disk is formatted, and format if needed with ext4
check if the disk is mounted, and mount if not
do nothing otherwise

I'm not sure what you mean by instead of doing formatting & mounting steps when that's the process you need to do to be able to use the disk. Are you saying you want something that just does it for you instead of having to write a script (or basically copy it from the linked docs)? — ydaetskcoR
@ydaetskcoR the process could be manual (me copy/pasting the commands), and automated (terraform formatting the disk, startup script auto-mounting it). I prefer the later, and was hoping someone has already done that, instead of every person reinventing the wheel :) P.S. in docs, edit /etc/fstab instructions are incorrect - it gets reset on instance reboot. — Yuri Astrakhan
The docs you linked to also mention why the file might be reset: “On Container-Optimized OS, modifications to /etc/fstab do not persist across reboots. To ensure the device is checked and mounted during boot, run the fsck and mount operations on the persistent disk from your cloud-config’s bootcmd section. See ‘Mounting and formatting disks’ in the Container-Optimized OS documentation.” — Dan
Unfortunately everybody under the sun uses a different OS configuration tool. For a basic shell script you should just copy-paste from the docs, but to integrate it with your other config scripts in Puppet / Chef / Ansible / Salt / ... a bit more work will be required. — Dan

neilH neilH · Accepted Answer · 2018-11-06T12:46:38

Have you considered using a startup script on the instance (I presume you can also add a startup-script with Terraform)? You could use an if loop to discover if the disk is formatted, then if not, you could try running the formatting/mounting commands in the documentation you linked (I realise you have suggested you do not want to follow the manual steps in the documentation, but these can be integrated into the startup script to achieve the desired result).

Running the following outputs and empty string if the disk is not formatted:

 sudo blkid /dev/sdb

You could therefore use this in a startup script to discover if the disk is formatted, then perform formatting/mounting if that is not the case. For example, you could use something like this (Note*** If the disk is formatted but not mounted this could be dangerous and should not be used if your use case could involve existing disks which may have already been formatted):

#!/bin/bash


if sudo blkid /dev/sdb;then 
        exit
else 
        sudo mkfs.ext4 -m 0 -F -E lazy_itable_init=0,lazy_journal_init=0,discard /dev/sdb; \
        sudo mkdir -p /mnt/disks/newdisk
        sudo mount -o discard,defaults /dev/sdb /mnt/disks/newdisk
fi

Automate GCP persistent disk initialization

2 Answers