user data script to initialize, partition and format ebs volume /dev/xvd[drive letter]

setup-volume.ps1

function setup-volume {
  param(
    [parameter(mandatory=$true,helpmessage="drive letter")]
    [string] $driveletter,
    [parameter(mandatory=$false,helpmessage="file system label")]
    [string] $label = ""
  )

  $driveletter = $driveletter.ToLower()

  # Assume last character of the device name = drive letter
  # SCSI targets for device names:
  # http://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ec2-windows-volumes.html#windows-volume-mapping
  $letters = @("b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z")
  # I.e. /dev/xvdb = scsi target 1
  $scsitarget = 1 + $letters.IndexOf( $driveletter )
  if( -not $scsitarget) {
    throw "Invalid drive letter. Could not look up scsitarget for $driveletter"
  }

  $disk = Get-Disk | ?{ $_.Location.EndsWith(("Target {0} : LUN 0" -f $scsitarget)) -and $_.OperationalStatus -eq "Offline" }

  if( -not $disk ) {
    throw "Could not find disk with SCSI target $scsitarget"
  }

  try {
    Initialize-Disk -Number $disk.Number -PartitionStyle "MBR"
  } catch {
    throw "Failed to initialize disk $_"
  }

  try {
    $part = New-Partition -DiskNumber $disk.Number -UseMaximumSize -IsActive -DriveLetter $driveletter
  } catch {
    throw "Failed to create partition $_"
  }

  try {
    Format-Volume -DriveLetter $part.DriveLetter -NewFileSystemLabel $label -Confirm
  } catch {
    throw "Failed to format drive $driveletter $_"
  }
}

user_data-template.hcl

  template = <<EOF
  <powershell>
  ${file("${path.module}/setup-volume.ps1")}
  setup-volume -driveLetter L -label Log
  setup-volume -driveLetter W -label Web
  </powershell>
EOF