This utility is intended to be used in the boot phase of an EC2 instance. It will generate a boot command sequence, which:
- waits for the EBS volume to be attached
- formats and labels the volume, if unformatted
- adds an /etc/fstab mount entry using LABEL=
- mounts the device if not mounted.
The utility will also on Nitro-based instance types, where the device name specified in the attach volume command is ignored. The volume will be assigned a device name which matches the pattern /dev/nvme[0-9]+n1, where the number is associated with the order in which the volumes was mounted.
On Nitro-based instance types, the volume will be queried for the assigned device name using ebsnvme-id. This will ensure that the mount command is the same and independent of the machine type and and order of volume attachment.
As the device name now potentially fluctuates on every boot, the use of hard coded nvme device names is hazarduous.
To generate the required boot commands, type:
$ ./generate-mount-ebs-volume-bootcmd /dev/xvdd /var/mqm wmq-data
The first parameter is your device name, the second the mount point and the third the label. It will generate a bootcmd snippet, you can add to your machine's cloud-config.
bootcmd:
- mkdir -p /var/mqm
- while [ ! -b $(readlink -f /dev/xvdd) ]; do echo "waiting for device /dev/xvdd"; sleep 5 ; done
- blkid $(readlink -f /dev/xvdd) || mkfs -t ext4 $(readlink -f /dev/xvdd)
- e2label $(readlink -f /dev/xvdd) wmq-data
- grep -q ^LABEL=wmq-data /etc/fstab || echo 'LABEL=wmq-data /var/mqm ext4 defaults' >> /etc/fstab
- grep -q "^$(readlink -f /dev/xvdd) /var/mqm " /proc/mounts || mount /var/mqm
It has to be hard-coded, as the write-files module of cloud-init is run after the bootcmd.