Make ephemeral swap and tmp.

mk-eph.sh

#!/bin/bash
# mk-eph.sh
# Creates a lvm volume over all ephemeral devices.

# Swap related operations
function SwapEnabler() {
  local swapdev='/dev/ephemeral/swap'
  local swapon="$(swapon -s | wc -l)"

  # See if some swap is enabled already.
  if (( ${swapon} > 1 )); then
    echo 'Swap already enabled'
    return 0
  fi

  if [[ -e '/dev/ephemeral/swap' ]]; then
    echo 'Enabling swap on vg group: ephemeral'
    mkswap -L 'ephemeral' "${swapdev}"
    swapon -L 'ephemeral'
  else
    echo 'vg group "ephemeral" not yet enabled. skipping swap.'
    return 1
  fi

  echo 'swap done'
}

# Trying to enable swap as the first thing.
SwapEnabler

# Will quit if /dev/ephemeral directory is already present.
if [[ -d '/dev/ephemeral' ]]; then
  echo 'VG group at /dev/ephemeral already present, quitting'
  exit 0
fi

# Initializing variables
device_count=0

# Getting the device list from aws metadata service..
edevices=$(curl -s http://169.254.169.254/latest/meta-data/block-device-mapping/ | grep ephemeral)

# Generating a usable list of all ephemeral devices.
for device in ${edevices}; do
  edev=$(curl -s http://169.254.169.254/latest/meta-data/block-device-mapping/${device})
  localdev="/dev/${edev/sd/xvd}"
  
  # Skip if the local device is not found
  if [[ ! -b "${localdev}" ]]; then
    continue
  fi
  
  # Doing the umount just in case
  umount ${localdev}

  # This script must be reboot proof, not adding already added volumes.
  pvd=$(pvdisplay -s ${localdev} 2>&1); ret=${?}
  if [[ ${ret} != 0 ]]; then
    ephemeral_devices="${ephemeral_devices} ${localdev}"
    (( device_count++ ))
  else
    echo "device ${localdev} already initialized"
  fi
done

# No point in continuing if there are no ephemeral devices.
if (( ${device_count} < 1 )); then
  echo "No ephemeral drives found, quitting."
  exit 0
fi

# See if we can use striping or not
if (( ${device_count} > 1 )); then
  lvprefix="lvcreate -i ${device_count}"
else
  lvprefix="lvcreate"
fi

# Use LVM striping
memtotal=$(cat /proc/meminfo | grep MemTotal | awk '{print $2}')

# Creating the pv and vg groups.
pvcreate $ephemeral_devices
vgcreate ephemeral $ephemeral_devices

# We need to check if we have enough space for tmp and swap.
vgtotal=$(vgdisplay -c ephemeral | awk -F ':' '{print $12}')
vgtmp=$(( ${vgtotal} - ${memtotal} ))

# See if we have more than 2GB available after enabling swap.
if (( ${vgtmp} < 2465792 )); then
  echo "Taking ${memtotal}kB for swap would leave only ${vgtmp}kB for tmp. Only swap enabled."
  ${lvprefix} -n swap -l 100%FREE ephemeral
else
  ${lvprefix} -n swap -L ${memtotal}K  ephemeral
  ${lvprefix} -n tmp -l 100%FREE ephemeral
fi

# Trying to enable swap as the last thing too.
SwapEnabler

# Done
echo "lvm volume done with devices: ${ephemeral_devices}"