SnapMaint.ps1

#
# The purpose of this script is to find all backups associated 
# with the calling instance-ID with the intent of expiring any images
# that are older than the threshold date. The script will pull the
# instance-ID from the instance meta-data URL, then search for
# Snapshots that were previously generated by the backup scripts
# found elsewhere in this tool-set.
#
# License:
# - This script released under the Apache 2.0 OSS License
#
######################################################################

# Commandline argument parsing...
Param (
   [int]$keepdays = 7,
   [string]$snapgrp 
)

# Set generic variables
$DaysBack = $keepdays
$SnapGroup = $snapgrp
$DateHorizon =  ([DateTime]::Now).AddDays(-$DaysBack)
$DateStmp = $(get-date -format "yyyyMMddHHmm")
$LogDir = "C:/TEMP/EBSbackup"
$LogFile = "${LogDir}/backup-$DateStmp.log"
$instMetaRoot = "http://169.254.169.254/latest/"

# Make sure AWS cmdlets are available
Import-Module "C:\Program Files (x86)\AWS Tools\PowerShell\AWSPowerShell\AWSPowerShell.psd1"


# Capture instance identy "document" data
$docStruct = Invoke-RestMethod -Uri ${instMetaRoot}/dynamic/instance-identity/document/

# Extract info from $docStruct
$instRegion = $docStruct.region
$instId = $docStruct.instanceId

# Set AWS region fo subsequent AWS cmdlets
Set-DefaultAWSRegion $instRegion

# Grab a filtered list candidate snapshots and dump to an array
# * Filter for "Created By" equals "Automated Backup"
# * Filter for "Description" contains "<INSTANCE_ID>-bkup"
function SnapListToArray {

   [System.Collections.Generic.List[System.String]]$global:DeleteList = ''
   # Fer realz, Microsoft? I can't declare an modifiable-length list as being empty (i.e., one without nulls trashing it up)???
   $DeleteList.Remove("") | Out-Null


   # Query for this instance's snapshots
   $SnapStructList = Get-EC2Snapshot -Filter @(
                        @{ Name="tag:Created By" ; Values="Automated Backup" }, `
                        @{ Name="description" ; Values="*${instId}*" }, `
                        @{ Name="tag:Snapshot Group" ; Values="*$SnapGroup*" }
                     )

   # Examine each snapshot's data structures
   foreach ($SnapStruct in $SnapStructList) {
      $SnapId = $SnapStruct.SnapshotId
      $SnapStart = $SnapStruct.StartTime
      Write-Host -NoNewline "Found snapshot: $SnapId (started @ ${SnapStart})"

      if ([DateTime]::Compare($DateHorizon, $SnapStart) -gt 0) {
         Write-Host " - $SnapId is older than defined horizon (adding to delete-list)"
         $DeleteList.Add("$SnapId") | out-null
      } else {
         Write-Host
      }

   }
}


function NukeSnaps {
   foreach ($NukeSnap in $DeleteList) {
      Write-Host -NoNewline "Deleting snapshot: $NukeSnap..."

      # Assign to var for diagnostics ...even though no exit info is printed
      # Not a fan of "Force" flags, but seems the only option, here
      $RemovalStatus = Remove-EC2Snapshot -SnapshotId $NukeSnap -Force -PassThru

      if ($RemovalStatus = '') {
         Write-Host "FAILED!"
      } else {
         Write-Host "Success"
      }

   }
}


SnapListToArray

if ($DeleteList.Count -eq 0) {
   Write-Host "Nothing to delete: no snapshots older than keep-horizon"
} else {
   Write-Host "Snapshot(s) to delete: $DeleteList"
   NukeSnaps
}