#Requires -Version 5.1
<#
    JbTecWiz Support Centre -- generated fix script

    Fault : HTTP 503 Service Unavailable -- the application pool has stopped
    Fix   : Fix the pool identity
    Source: https://jbtecwiz.com/support/srv-iis-503

    Run as     : Elevated PowerShell
    Expect     : 20 minutes
    Risk       : low
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    The pool will not start. An expired or changed service-account password
    is the usual reason.

    HOW TO UNDO IT
    Set the identity back to ApplicationPoolIdentity.

    This script walks the fix one step at a time and asks before each
    one. Steps with no command are things you do yourself -- it prints
    those and waits. Run with -DryRun to print without executing.

    --------------------------------------------------------------------
    NO WARRANTY - USE AT YOUR OWN RISK

    This script is provided by JbTecWiz as-is and with no warranty of any
    kind, express or implied. You run it entirely at your own risk.

    JbTecWiz accepts no liability for any loss or damage arising from its
    use, including but not limited to data loss, downtime, or configuration
    changes that turn out to be wrong for your system.

    You are responsible for reading this script before running it, for
    satisfying yourself that it suits the machine in front of you, and for
    having a working backup first. Some steps cannot be undone.
    --------------------------------------------------------------------
#>

[CmdletBinding()]
param(
    # Print every step and command without running anything.
    [switch]$DryRun,
    # Do not ask before each step. Read the script first if you use this.
    [switch]$Unattended
)

$ErrorActionPreference = 'Stop'
$script:Failed = 0

function Write-Rule { param([string]$Text)
    Write-Host ''
    Write-Host ('-' * 70) -ForegroundColor DarkGray
    if ($Text) { Write-Host $Text -ForegroundColor Cyan }
}

function Show-Prose { param([string]$Text, [string]$Colour = "Gray")
    if (-not $Text) { return }
    $words = $Text -split "\s+"; $line = "  "
    foreach ($w in $words) {
        if (($line.Length + $w.Length) -gt 74) { Write-Host $line -ForegroundColor $Colour; $line = "  " }
        $line += "$w "
    }
    if ($line.Trim()) { Write-Host $line -ForegroundColor $Colour }
}

function Invoke-Step {
    param(
        [int]$Number, [string]$Do, [string]$Why,
        [scriptblock]$Command, [switch]$Manual, [string]$Shell = "powershell"
    )
    Write-Rule "  Step $Number of 5"
    Show-Prose $Do "White"
    if ($Why) { Write-Host ""; Show-Prose $Why "DarkGray" }

    if ($Manual) {
        Write-Host ''
        Write-Host '  -> Do this yourself, then press Enter to carry on.' -ForegroundColor Yellow
        if (-not $Unattended -and -not $DryRun) { [void](Read-Host) }
        return
    }

    Write-Host ''
    foreach ($l in ($Command.ToString().Trim() -split "`n")) {
        Write-Host ("    " + $l.Trim()) -ForegroundColor Green
    }
    Write-Host ''

    if ($DryRun) { Write-Host "  (dry run -- not executed)" -ForegroundColor DarkGray; return }
    if (-not $Unattended) {
        $a = Read-Host "  Run this step? [Y]es / [S]kip / [Q]uit"
        if ($a -match "^[Qq]") { Write-Host "  Stopped at your request."; exit 0 }
        if ($a -match "^[Ss]") { Write-Host "  Skipped." -ForegroundColor DarkGray; return }
    }
    try { & $Command }
    catch {
        $script:Failed++
        Write-Host ("  Step $Number failed: " + $_.Exception.Message) -ForegroundColor Red
        Show-Prose "The rest of the fix may depend on this. Read the write-up before carrying on." "Red"
        if (-not $Unattended) {
            $c = Read-Host "  Carry on anyway? [y/N]"
            if ($c -notmatch "^[Yy]") { exit 1 }
        }
    }
}

Write-Rule
Write-Host '  HTTP 503 Service Unavailable -- the application pool has stopped' -ForegroundColor White
Write-Host '  Fix the pool identity' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: low   Reversible   20 minutes'
Write-Host ''
Show-Prose 'No warranty. Use at your own risk - JbTecWiz accepts no liability. Read it before you run it, and have a backup.' 'DarkYellow'
Write-Rule

if (-not $Unattended -and -not $DryRun) {
    $go = Read-Host '  Ready? [y/N]'
    if ($go -notmatch "^[Yy]") { Write-Host "  Nothing was changed."; exit 0 }
}

Invoke-Step -Number 1 -Do 'Read the events -- 5021 is a bad identity password, 5057 a .NET load failure.' -Command {
    Get-WinEvent -LogName System -MaxEvents 40 | Where-Object { $_.ProviderName -like '*WAS*' -or $_.ProviderName -like '*IIS*' } | Format-List TimeCreated, Id, Message
}

Invoke-Step -Number 2 -Do 'Check what identity the pool runs as.' -Command {
    Import-Module WebAdministration
    Get-ChildItem IIS:\AppPools | ForEach-Object { [PSCustomObject]@{ Pool=$_.Name; State=$_.State; Identity=$_.processModel.identityType; User=$_.processModel.userName } } | Format-Table -AutoSize
}

Invoke-Step -Number 3 -Do 'Re-enter the password for a custom identity.' -Command {
    Set-ItemProperty 'IIS:\AppPools\MyPool' -Name processModel.password -Value 'ThePassword'
}

Invoke-Step -Number 4 -Do 'Better, move it to a group Managed Service Account so the password is never a problem again.' -Why 'A gMSA''s password is rotated by AD and never typed anywhere, which removes the annual outage this fault represents.' -Command {
    Set-ItemProperty 'IIS:\AppPools\MyPool' -Name processModel.identityType -Value SpecificUser
    Set-ItemProperty 'IIS:\AppPools\MyPool' -Name processModel.userName -Value 'EXAMPLE\svc_web$'
    Set-ItemProperty 'IIS:\AppPools\MyPool' -Name processModel.password -Value ''
}

Invoke-Step -Number 5 -Do 'Start the pool.' -Command {
    Start-WebAppPool -Name MyPool
}

Write-Rule "  Confirm it worked"
Show-Prose 'The pool is Started and the site answers.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-ChildItem IIS:\AppPools | Format-Table Name, State -AutoSize
    Invoke-WebRequest http://localhost/ -UseBasicParsing | Select-Object StatusCode
}

Write-Rule
if ($script:Failed -gt 0) {
    Write-Host ("  Finished with " + $script:Failed + " failed step(s).") -ForegroundColor Yellow
    Show-Prose 'Read the full write-up at https://jbtecwiz.com/support/srv-iis-503' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: Set the identity back to ApplicationPoolIdentity.' 'DarkGray'
Write-Rule