Add AAS IP Firewall exception and add currently executing service principal to AAS admin list

Add-AASFirewallExceptionAndAdmin.ps1

[CmdletBinding()]
Param(
    [Parameter(Mandatory)]
    [string] $ResourceGroupName
)

# Add Firewall exception for current IP address
$myIpAddress = Invoke-RestMethod https://ipinfo.io/json | Select-Object -ExpandProperty ip
$azAnalysisFirewallRule = New-AzAnalysisServicesFirewallRule -FirewallRuleName "az-devops-hosted-agent-$(New-Guid)" -RangeStart $myIpAddress -RangeEnd $myIpAddress
$azAnalysisServicesServer = Get-AzAnalysisServicesServer -ResourceGroupName $ResourceGroupName
if ($azAnalysisServicesServer.FirewallConfig.FirewallRules.RangeStart -contains $myIpAddress) {
    Write-Verbose "IP whitelist exception for '$myIpAddress' already added"
}
else {
    if ($null -eq $azAnalysisServicesServer.FirewallConfig) {
        $azAnalysisServicesFirewallConfig = New-AzAnalysisServicesFirewallConfig
        $azAnalysisServicesServer.FirewallConfig.FirewallRules = $azAnalysisFirewallRule
    }
    else {
        $azAnalysisServicesServer.FirewallConfig.FirewallRules.Add($azAnalysisFirewallRule)
    }
    Write-Verbose "Adding AAS firewall rule '$($azAnalysisServicesServer.FirewallConfig.FirewallRules.FirewallRuleName)' for current IP '$myIpAddress' on server $($azAnalysisServicesServer.Name)"
    Set-AzAnalysisServicesServer -FirewallConfig $azAnalysisServicesServer.FirewallConfig -Name $azAnalysisServicesServer.Name
    Write-Verbose "Successfully added AAS firewall rule"
}

# Add currently executing service principal to AAS admin list
$azContext = Get-Azcontext
$spApplicationId = ($azContext).Account.Id
$aasAdminToAdd = "app:$spApplicationId@$($azContext.Tenant.Id)"
$azAnalysisServicesServer.AsAdministrators.Add($aasAdminToAdd)
Write-Verbose "Adding '$aasAdminToAdd' (current service principle) to AAS admins"
Set-AzAnalysisServicesServer -Administrator ([string]::Join(',', $azAnalysisServicesServer.AsAdministrators)) -Name $azAnalysisServicesServer.Name
Write-Verbose "Successfully added current service principle to AAS admins"

Dear Christoph,
I faced situation that if your AS server doesn't yet have any rules, this line of the script $azAnalysisServicesServer.FirewallConfig.FirewallRules.Add($azAnalysisFirewallRule) doesn't work with error "You cannot call a method on a null-valued expression.". Possibly - because $azAnalysisServicesServer.FirewallConfig.FirewallRules returns an empty object (or list with empty elements, I don't clearly get it myself) and method .Add can't be "as is" applied to it.
And this actually happens, because your another script, where you removes the rule, do this in this way:
$azAnalysisServicesServer.FirewallConfig.FirewallRules = $azAnalysisServicesServer.FirewallConfig.FirewallRules | Where-Object { -not $_.FirewallRuleName.StartsWith('az-devops-hosted-agent') },
so if you have only 1 rule, it sets $azAnalysisServicesServer.FirewallConfig.FirewallRules to $null.
For instance, if you'll use .Remove method, like you do for admin membership, everything works perfectly.

Hi @denis-sch , thanks for the feedback. It seems you encountered the special case where there is no initial firewall config at all (in my case there was always at least one). In that case $azAnalysisServicesServer.FirewallConfig is $null, I've updated the script with some if/else code to make it agnostic of that.