(docs): Expand on cloud-init explanation

README.md

@@ -57,7 +57,7 @@ sudo install -m755 /tmp/ebs-bootstrap /usr/local/sbin/ebs-bootstrap
 
 A potential way of operating `ebs-bootstrap` is through a `systemd` service. This is so we can configure it as a `oneshot` service type that executes after the file system is ready and after `clout-init.service` writes any config files to disk. The latter is essential as `ebs-bootstrap` consumes a config file that is located at `/etc/ebs-boostrap/config.yml` by default. 
 
-`ExecStopPost=-...` con point towards a script that is executed when the `ebs-bootstrap` service exits on either success or failure. This is a suitable place to include logic to notify an engineer that the configured devices failed their relevant healthchecks and the underlying application failed to launch in the process.
+`ExecStopPost=-...` con point towards a script that is executed when the `ebs-bootstrap` service exits on either success or failure. This is a suitable place to include logic to notify an individual that the configured devices failed their relevant healthchecks and the underlying application failed to launch in the process.
 
 ```ini
 [Unit]
@@ -162,7 +162,25 @@ Resources:
           EbsBootstrapUrlPrefix: https://github.com/reecetech/ebs-bootstrap/releases/latest/download/ebs-bootstrap-linux
 ```
 
-By inspecting the output of `lsblk`, we can verify that `ebs-bootstrap` was able to recover the CloudFormation assigned block device mappings (`/dev/sdb` and `/dev/sdh`) from both EBS and Instance Store NVMe devices (`/dev/nvme1n1` and `/dev/nvme2n1`). This is all under the assumption that a human operator was able to format and label the EBS volume beforehand.
+Assuming this is the very first launch, `ebs-bootstrap` would refuse to perform any modifications associated to the EBS device as it was assigned the `healthcheck` mode. However, we can temporarily override this behaviour with the `-mode=prompt` option. This allows the Platform Engineer to approve any suggested changes by `ebs-bootstrap`.
+
+```
+[~] sudo /usr/local/sbin/ebs-bootstrap -mode=prompt
+🔵 /dev/nvme1n1: Detected Nitro-based AWS NVMe device => /dev/sdb
+🔵 /dev/nvme2n1: Detected Nitro-based AWS NVMe device => /dev/sdh
+🟠 Formatting larger disks can take several seconds ⌛
+🟣 Would you like to format /dev/nvme1n1 to ext4? (y/n): y
+⭐ Successfully formatted /dev/nvme1n1 to ext4
+🟠 Certain file systems require that devices be unmounted prior to labeling
+🟣 Would you like to label device /dev/nvme1n1 to 'stateful'? (y/n): y
+⭐ Successfully labelled /dev/nvme1n1 to 'stateful'
+...
+🟣 Would you like to change ownership (1000:1000) of /mnt/ebs? (y/n): y
+⭐ Successfully changed ownership (1000:1000) of /mnt/ebs
+🟢 Passed all validation checks
+```
+
+By inspecting the output of `lsblk`, we can verify that `ebs-bootstrap` was able to recover the CloudFormation assigned block device mappings (`/dev/sdb` and `/dev/sdh`) from both EBS and Instance Store NVMe devices (`/dev/nvme1n1` and `/dev/nvme2n1`) and format/label/mount the respective devices
 ```
 [~] lsblk -o NAME,FSTYPE,MOUNTPOINT,LABEL,SIZE
 NAME         FSTYPE MOUNTPOINT                  LABEL            SIZE
@@ -173,4 +191,19 @@ nvme0n1                                                            8G
 └─nvme0n1p15 vfat   /boot/efi                   UEFI             106M
 nvme1n1      ext4   /mnt/ebs                    stateful          10G
 nvme2n1      ext4   /mnt/instance-store         ephemeral       69.9G
+
+[~] ls -la /mnt
+total 16
+drwxr-xr-x  4 root   root   4096 Jan  8 04:57 .
+drwxr-xr-x 19 root   root   4096 Jan  8 04:36 ..
+drwxr-xr-x  3 ubuntu ubuntu 4096 Jan  8 04:57 ebs
+drwxr-xr-x  3 ubuntu ubuntu 4096 Jan  8 04:39 instance-store
+```
+
+The `mounts` module of `cloud-init` will create an entry in `/etc/fstab` for the EBS volume. The EBS volume, now labelled `stateful`, will be mounted to `/mnt/ebs` on **future reboots**. Despite device names being unstable because of the dynamical allocation behaviour of the Nitro NVMe driver, their respective labels remain stable across reboots.
+```
+[~] cat /etc/fstab
+LABEL=cloudimg-rootfs	/	 ext4	defaults,discard	0 1
+LABEL=UEFI	/boot/efi	vfat	umask=0077	0 1
+LABEL=stateful	/mnt/ebs	ext4	defaults,nofail,x-systemd.device-timeout=5,comment=cloudconfig	0	2
 ```