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

    Fault : AD replication error 8524 -- the DSA operation cannot continue (DNS lookup failure)
    Fix   : Rebuild the missing _msdcs CNAME for the partner
    Source: https://jbtecwiz.com/support/srv-ad-8524

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

    WHEN THIS IS THE RIGHT FIX
    One specific partner fails and the rest are fine.

    HOW TO UNDO IT
    None -- this adds DNS records that should exist.

    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(
    # <objectguid> from the write-up. PowerShell prompts for this
    # by name if you do not pass it on the command line.
    [Parameter(Mandatory = $true)][string]$objectguid,
    # 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 '  AD replication error 8524 -- the DSA operation cannot continue (DNS lookup failure)' -ForegroundColor White
Write-Host '  Rebuild the missing _msdcs CNAME for the partner' -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 'Get the partner''s directory server GUID.' -Command {
    repadmin /showrepl DC01 /repsto
}

Invoke-Step -Number 2 -Do 'Try to resolve the alias that GUID should have.' -Why 'This alias is how one DC finds another for replication. If it does not resolve, replication has no way to start, whatever else is healthy.' -Command {
    Resolve-DnsName -Name "$objectguid._msdcs.example.local" -Type CNAME
}

Invoke-Step -Number 3 -Do 'On the partner DC, force it to re-register its own records.' -Command {
    nltest /dsregdns
    Restart-Service Netlogon
}

Invoke-Step -Number 4 -Do 'If the record still does not appear, confirm the _msdcs zone is present and is replicating to the whole forest.' -Command {
    Get-DnsServerZone | Where-Object ZoneName -like '*_msdcs*' | Format-List ZoneName, ReplicationScope, ZoneType
}

Invoke-Step -Number 5 -Do 'Force replication once the record resolves.' -Command {
    repadmin /syncall /AdeP
}

Write-Rule "  Confirm it worked"
Show-Prose 'repadmin /replsummary shows no failures for that pair.' 'White'
Write-Host ''
if (-not $DryRun) {
    repadmin /replsummary
}

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-ad-8524' 'Yellow'
} else {
    Write-Host '  Finished.' -ForegroundColor Green
}
Write-Host ''
Show-Prose 'To undo: None -- this adds DNS records that should exist.' 'DarkGray'
Write-Rule