Automatically mount EC2 free ephemeral disks into an LVM group

readme.md

I have found the original script from a post by Leon Mergen. See also raid_ephemeral.sh from Joe Miller

I updated it for my needs, which were:

• Work independently of device name (/dev/sdX, /dev/xvdX or /dev/nvmeXXX)
• Avoid mounting a device which is already in use (some ami will mount the first epehermal device)
• Avoid using metadata, as it's not trustworthy when using launch templates. This means the script does not know if the devices are EBS or Ephemeral. I would recommend not to use this if you have a mixed EBS/Ephemeral instance, as the volume will be corrupted if the instance is stoped.

lvmount.sh

#!/bin/bash
# based on code byLeon Mergen
# see: https://leonmergen.com/automatically-mounting-instance-store-on-an-aws-ami-150da3ffd041

LVDISPLAY=$(which lvdisplay)
PVCREATE=$(which pvcreate)
VGCREATE=$(which vgcreate)
LVCREATE=$(which lvcreate)
MOUNT=$(which mount)
MKDIR=$(which mkdir)
CHMOD=$(which chmod)
LVNAME="data"
MKFSCMD=$(which mkfs)
MKFS="$MKFSCMD -t xfs"
MOUNTPOINT="/scratch"
DEVICE_PREFIX="/dev"

if [ -b $DEVICE_PREFIX/dm-0 ] ; then	
	echo "LVM already configured, exiting ...."	
	exit 3
fi
echo No LVM configured, yet

function mount_volume { 
	if [ ! -d "$MOUNTPOINT" ]
	then	
		$MKDIR -p ${MOUNTPOINT}
		$CHMOD 0777 ${MOUNTPOINT}
	fi
	$MOUNT $1 ${MOUNTPOINT} 
}

# Detects all local block devices present on the machine,
# skipping the first (which is assumed to be root). 
function detect_devices { 
	# Get root device in order to identify naming scheme and to ignore then using.

	local ROOT_DRIVE=$(blkid -L / -o device | cut -d "/" -f 3 | cut -c 1-7 )
	# Find if there are devices
        if [ -z $ROOT_DRIVE  ] ; then
                echo "No devices found, exiting ...."
                exit 4
        fi
        local DEVICES_LIST=$(find /dev -type b |  grep -v "$ROOT_DRIVE")
	# Check if any of the devices is mounted
	# Exit if there is only one devices, and it's mounted
        for DEVICE in $DEVICES_LIST
        do
                if ! grep -q $(readlink -f $DEVICE) /proc/mounts
                then
                                local DEVICES="$DEVICE $DEVICES"
                else
                        if [ $i == 1 ]
			then
				echo "Ephemeral device already in use, exiting .."
                                exit 5
                        fi
                fi
        done
        echo $DEVICES

} 

# Creates a new LVM volume. Accepts an array of block devices to 
# use as physical storage. 
function create_volume { 	
	for device in $@ 	
	do
		$PVCREATE $device --yes	
	done 
	
	# Creates a new volume group which pools all 	
	# available block devices. 	
	${VGCREATE} $LVNAME $@ 
	
	# Create a logical volume with all the available storage space 	
	# assigned to it. 	
	${LVCREATE} -l 100%FREE $LVNAME --yes
	
	# Create a filesystem so we can use the partition. 	
	${MKFS} $(get_volume) 
} 

function detect_volume { 	
	local VOLCHECK=$($LVDISPLAY)
	if [ ! -z "$VOLCHECK" ]
	then 
		local VOLUME=$(${LVDISPLAY} | grep 'LV Path' | awk '{print $3}')
		echo $VOLUME
	fi
} 

# Similar to detect_volume, but fails if no volume is found. 
function get_volume { 	
	local VOLUME=$(detect_volume) 	
	if [ -z "$VOLUME" ] 	
	then 	
	  echo "Fatal error: LVM volume not found!" 1>&2 	
	  exit 1 	
	fi 	
	echo $VOLUME 
} 

# Detect existing LVM volume 
echo Start detect volume
VOLUME=$(detect_volume) 
echo End detect volume

echo Start new volume
# And create a brand new LVM volume if none were found 
if [ -z "$VOLUME" ] 
then 	
	echo Start create volume on DEVICE_SUFFIX $DEVICE_PREFIX
	create_volume $(detect_devices $DEVICE_PREFIX) 
	echo End create volume
else
	echo what is "$VOLUME"
fi 
echo End new volume

mount_volume $(get_volume)