format_ephemeral.sh

#!/bin/bash -ue

# this script will attempt to detect any ephemeral drives on an EC2 node

mount_point=${1:-"/mnt/storage"}
METADATA_URL_BASE="http://169.254.169.254/latest"
INSTANCEID=$(wget -q -O - ${METADATA_URL_BASE}/meta-data/instance-id)

# Configure Raid - take into account xvdb or sdb
root_drive=$(df -h | grep -P '^.*/$' | awk 'NF==6{print $1}')

if [ "${root_drive}" == "/dev/xvda1" ]; then
    echo "Detected 'xvd' drive naming scheme (root: ${root_drive})"
    DRIVE_SCHEME='xvd'
else
    echo "Detected 'sd' drive naming scheme (root: ${root_drive})"
    DRIVE_SCHEME='sd'
fi

# figure out how many ephemerals we have by querying the metadata API, and then:
#  - convert the drive name returned from the API to the hosts DRIVE_SCHEME, if necessary
#  - verify a matching device is available in /dev/
drives=""
ephemeral_count=0
ephemerals=$(curl --silent ${METADATA_URL_BASE}/meta-data/block-device-mapping/ | grep ephemeral)
# see http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/device_naming.html

for e in ${ephemerals}; do
    echo "Probing ${e} .."
    device_name=$(curl --silent ${METADATA_URL_BASE}/meta-data/block-device-mapping/${e})
    if [ ! -z "${device_name}" ]; then
      echo "meta-data API thinks there is a disk here: ${device_name}"
    fi
    # might have to convert 'sdb' -> 'xvdb'
    device_name=$(echo ${device_name} | sed "s/sd/$DRIVE_SCHEME/")
    device_path="/dev/${device_name}"
    echo "Converting device name from ${device_name} to ${device_path}"

    # test that the device actually exists since you can request more ephemeral drives than are available
    # for an instance type and the meta-data API will happily tell you it exists when it really does not.
    if [ -b ${device_path} ]; then
        echo "Detected ephemeral disk: ${device_path}"
        drives="$drives ${device_path}"
        ephemeral_count=$((ephemeral_count + 1 ))
    else
        echo "Could not find the disk's device path ($device_path). Let's check if we find some NVME disks..."
        declare -a DEVICES=($(find /dev -type b -name nvme[0-7]n1 | awk -F/ '{print $3}'))
        for i in "${DEVICES[@]}"; do
          device_name=${i}
          device_path=$(readlink -f "/dev/${i}")
          # test again if it
          if [ -z "${device_name}" ]; then
            echo "Ephemeral disk ${e}, ${device_path} is not present. skipping"
          else
            echo "Detected ephemeral disk: ${device_path}"
            drives="$drives ${device_path}"
            ephemeral_count=$((ephemeral_count + 1 ))
          fi
        done
    fi
done

# need at least one disk
if [ "${ephemeral_count}" = 0 ]; then
    echo "No ephemeral disk detected. exiting"
    exit 0
fi

# umount mount point if mounted
if [[ $(cat /proc/mounts  | grep ${mount_point}) ]]
then
    umount ${mount_point}
    sed -i '/\/mnt\/storage/d' /etc/fstab
fi

# create the new mount point if needed
if [[ ! -e ${mount_point} ]]
then
    mkdir -p ${mount_point}
fi

# Configure drives
for drive in ${drives}; do
    # wipe, create, tune and mount
    dd if=/dev/zero of=${drive} bs=4096 count=1024
    mkfs -t ext4 ${drive}
    tune2fs -o journal_data_writeback ${drive}
    tune2fs -O ^has_journal ${drive}
    e2fsck -p -f ${drive}
    mount -t ext4 -o noatime ${drive} ${mount_point}
    # edit fstab
    udid=$(blkid | grep ${drive} | awk -F ' ' '{print $2}' | tr -d \")
    echo "${udid} ${mount_point} ext4 defaults,noatime,nofail 0 0" | tee -a /etc/fstab
done