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

    Fault : HTTP 503 Service Unavailable -- the application pool has stopped
    Fix   : Stop the worker crashing and clear rapid-fail protection
    Source: https://jbtecwiz.com/support/srv-iis-503

    Run as     : Elevated PowerShell
    Expect     : 45 minutes
    Risk       : medium
    Reversible : yes

    WHEN THIS IS THE RIGHT FIX
    The pool starts then stops. Something is killing the worker process and
    IIS is refusing to keep restarting it.

    HOW TO UNDO IT
    Set rapidFailProtectionMaxCrashes back to 5.

    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 '  Stop the worker crashing and clear rapid-fail protection' -ForegroundColor Cyan
Write-Host ''
Write-Host '  Risk: medium   Reversible   45 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 'Find the crash. Event 5002 is rapid-fail protection tripping; the Application log has the actual exception.' -Command {
    Get-WinEvent -LogName Application -MaxEvents 30 | Where-Object { $_.Id -in 1000,1026 } | Format-List TimeCreated, Id, Message
}

Invoke-Step -Number 2 -Do 'Read the rapid-fail settings -- five failures in five minutes is the default and is easily hit.' -Command {
    Get-ItemProperty 'IIS:\AppPools\MyPool' -Name failure | Format-List rapidFailProtection, rapidFailProtectionInterval, rapidFailProtectionMaxCrashes
}

Invoke-Step -Number 3 -Do 'Start the pool and watch whether it survives.' -Command {
    Start-WebAppPool -Name MyPool
    Start-Sleep 20
    Get-ChildItem IIS:\AppPools | Where-Object Name -eq MyPool | Format-Table Name, State
}

Invoke-Step -Number 4 -Do 'Fix the underlying crash. If it is a .NET version mismatch, confirm the runtime the pool is set to matches the application.' -Command {
    Get-ItemProperty 'IIS:\AppPools\MyPool' -Name managedRuntimeVersion, enable32BitAppOnWin64 | Format-List
}

Invoke-Step -Number 5 -Do 'Only widen rapid-fail protection once the crash is understood -- never as the fix itself.' -Why 'Rapid-fail protection exists to stop a broken application consuming the server. Raising the limit hides the crash and leaves the server restarting a failing worker twenty times instead of five.' -Command {
    Set-ItemProperty 'IIS:\AppPools\MyPool' -Name failure.rapidFailProtectionMaxCrashes -Value 20
}

Write-Rule "  Confirm it worked"
Show-Prose 'The pool stays started under load and no 5002 events appear.' 'White'
Write-Host ''
if (-not $DryRun) {
    Get-WinEvent -LogName System -MaxEvents 20 | Where-Object Id -eq 5002
}

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 rapidFailProtectionMaxCrashes back to 5.' 'DarkGray'
Write-Rule