Sensu check to ensure iSCSI connections are present & connected

check-iscsi.ps1

#
#  check-iscsi.ps1
#
# DESCRIPTION:
#   This plugin checks that each ISCSI IQN passed to it is currently connected.
#
# OUTPUT:
#   plain text
#
# PLATFORMS:
#   Windows
#
# DEPENDENCIES:
#
# USAGE:
#   Please run this check with the '-help' parameter for more info.
#
# NOTES:
#
# LICENSE:
#   Copyright 2016 James Booth <james@absolutejam.co.uk>
#   Released under the same terms as Sensu (the MIT license); see LICENSE for details.
#

[CmdletBinding()]
Param(
  [Parameter(
    Mandatory = $False,
    Position = 1
  )]
  [string]$IQN,

  [switch]$Help
)

if ($Help) {
    Write-Output @"
Checks whether an ISCSI connection is connected.

Arguments:
  -iqn    A string with comma separated ISCS iqn values
  -Help   Show help

Note:
  Because this check is designed to make full use of Sensu's check token 
  substitution (https://sensuapp.org/docs/latest/reference/checks.html#check-token-substitution)
  feature some special considerations have been taken for how the arguments are parsed.

  Where noted above, these parameters support a list of of comma-separated strings.
    eg. -param1 'value1','value2'
  They also accepts accept a single string with comma-separated values.
    eg. -param1 'value1,value2'
  ...or you can mix & match the two and all of the values will be merged.
    eg. -param1 'value1','value2,value3'
  Additionally, any use of the word 'None' will be ignored out.
    eg. -param1 'value1','None'

  This is because Sensu's client attribute substitution tokens only work with 
  flat strings, but by supporting both of the above methods, it allows the use
  of multiple values within a single check/client attribute AND multiple
  different client/check attributes to be used. Additionally, because 'None'
  is ignored, it allows the user to provide a default value in the check 
  token substitution, as not to throw an error if the value is missing.


Token substitution example:
  
  Check attribute 'check_attr'   = "alpha,bravo"
  Client attribute 'client_attr' = "charlie,delta"

    powershell.exe -File check.ps1 -param1 ":::check_attr|None:::,:::missing_attr|None:::,:::client_attr|None:::"
    
  Which expands to:

    powershell.exe -File check.ps1 -param "alpha,bravo,None,charlie,delta"

  The script then strips any instances of 'None' and processes the 
  comma-separated string as an array.


Example usage:
  ./check-iscsi.ps1 -iqn iqn1,iqn2
  ./check-services.ps1 -criticalservices :::vars.iscsi.iqn1:::,:::vars.iscsi.iqn2|None:::

"@
    Exit 0
}

Function Format-ParamArray ($Param) {
    # Flatten the (potential) array into a string
    $Param = $Param -Join ','
    # Strip any instances of 'None'
    $Param = $Param -Replace 'None[,]?',''
    # Replace multiple consecutive commas with a single comma
    $Param = $Param -Replace '[,]{2,}',','
    # If the last character is a comma, remove it
    if ($Param[-1] -eq ',') {
        $Param = $Param.substring(0, $Param.Length-1)
    }
    # Split into an array
    $Param = $Param -split ','

    return $Param
}

# Setup
$CheckName = 'CheckIscsi'
$Status = 0
$Output = New-Object -TypeName System.Collections.ArrayList

# Merge the cli parameters into a single string
$IQNList = Format-ParamArray -Param $IQN


if (!($IQN)) {
    Write-Output "$CheckName OK: No iSCSI connections specified."
    Exit 0
}



$AllSessions = Get-IscsiSession | Select-Object -ExpandProperty TargetNodeAddress
$DisconnectedSessions = Get-IscsiSession | 
                        Where-Object { $_.IsConnected -ne $True } | 
                        Select-Object -ExpandProperty TargetNodeAddress
if ($DisconnectedSessions.Length -eq 0) { $DisconnectedSessions = @() }



# Check that all of the sessions specified are present
$MissingSessions = Compare-Object -ReferenceObject $IQNList -DifferenceObject $AllSessions |
                   Where-Object { $_.SideIndicator -eq '<=' } |
                   Select-Object -ExpandProperty InputObject
if ($MissingSessions.Length -eq 0) { $MissingSessions = @() }

if ($MissingSessions.Length -gt 0) {
    $Status = 1
    $Message = "$CheckName CRITICAL: The following sessions are missing:`r`n" + ($MissingSessions -join "`r`n")
    $Output.Add($Message) | Out-Null
}



# Now, check that all of the sessions that are present are connected
$CriticalSessions = Compare-Object -ReferenceObject $IQNList -DifferenceObject $DisconnectedSessions -IncludeEqual |
                    Where-Object { $_.SideIndicator -eq '==' } |
                    Select-Object -ExpandProperty InputObject

if ($CriticalSessions.Length -gt 0) {
    $Status = 2
    $Message = "$CheckName CRITICAL: The following iSCSI sessions are disconnected:`r`n" + ($CriticalSessions -join "`r`n")
    $Output.Insert(0, $Message) | Out-Null
}




# No issues so far!
if ($Output.Length -eq 0) {
    $Output.Add("$CheckName OK: All iSCSI sessions are connected!")
}



# Return!
Write-Output ($Output -join "`r`n")
Exit $Status