How do I use Set- commands with AzureRM and Application Gateway? - azure

Question

I am trying to run the following commands to change the settings on an existing Rule in my Azure Application Gateway:
$updatedAppGW = Set-AzureRmApplicationGatewayRequestRoutingRule -ApplicationGateway $AppGW `
-Name $ChosenSubscription.httpsRule `
-RuleType Basic `
-BackendAddressPool $backendPool `
-BackendHttpSettings $httpSettings
# Save Gateway configuration
Write-Host "[$(__LINE__)] Attempting to save changes to the Application Gateway..." -ForegroundColor Cyan
Set-AzureRmApplicationGateway -ApplicationGateway $updatedAppGW | Out-Null
The Set-AzureRmApplicationGatewayRequestRoutingRule command appears to run correctly (silently, at least).
However, when I then try to "save" the Application Gateway configuration with the command Set-AzureRmApplicationGateway I receive the error Set-AzureRmApplicationGateway : Object reference not set to an instance of an object.
I think this is because I'm not using these "Set" commands correctly.
I read online that when I run Set-AzureRmApplicationGatewayRequestRoutingRule, I'm only actually making changes to the Rule in local memory. I then have to save the changes of the Application Gateway.
Is this true? If so... how do I actually save the Application Gateway configuration in this context? Earlier in my script, when using Add-AzureRm commands (such as Add-AzureRmApplicationGatewayBackendAddressPool), I've immediately (following line) run Set-AzureRmApplicationGateway and it has worked as intended.
I have also tried altering the Set-AzureRmApplicationGateway command in the code block at the top of this post to use my original $AppGW variable instead of this $updatedAppGW variable which I think my Set-AzureRmApplicationGatewayRequestRoutingRule command is producing. Neither works - identical error.
EDIT: Additional diagnosis
Adding the following Write-Host output...
Write-Host "[$(__LINE__)] Retrieved AG Rule '$($rule.Name)'." -ForegroundColor Magenta
Write-Host "[$(__LINE__)] Attempting to change this rule to point at Backend Address Pool '$($backendPool.Name)' and HTTP Settings '$($httpSettings.Name)'..." -ForegroundColor Cyan
# Re-retrieve the Application Gateway after saving it earlier
$AppGW = Get-AzureRmApplicationGateway -Name $ChosenSubscription.appGateway -ResourceGroupName $ChosenSubscription.resourceGroup
# Re-retrieve the Backend Address Pool and HTTP Settings that we've created, for the sake of updating the rule
$backendPool = Get-AzureRmApplicationGatewayBackendAddressPool -ApplicationGateway $AppGW -Name $MaintenanceToggleBackendPool
$httpSettings = Get-AzureRmApplicationGatewayBackendHttpSettings -ApplicationGateway $AppGW -Name $MaintenanceToggleHTTPSetting
Write-Host "[$(__LINE__)] `$AppGW.Name $($AppGW.Name)" -ForegroundColor Green
Write-Host "[$(__LINE__)] `$AppGW.ProvisioningState $($AppGW.ProvisioningState)" -ForegroundColor Green
Write-Host "[$(__LINE__)] `$AppGW.OperationalState $($AppGW.OperationalState)" -ForegroundColor Green
$updatedAppGW = Set-AzureRmApplicationGatewayRequestRoutingRule -ApplicationGateway $AppGW `
-Name $ChosenSubscription.httpsRule `
-RuleType Basic `
-BackendAddressPool $backendPool `
-BackendHttpSettings $httpSettings
Write-Host "[$(__LINE__)] `$updatedAppGW.Name $($updatedAppGW.Name)" -ForegroundColor Green
Write-Host "[$(__LINE__)] `$updatedAppGW.ProvisioningState $($updatedAppGW.ProvisioningState)" -ForegroundColor Green
Write-Host "[$(__LINE__)] `$updatedAppGW.OperationalState $($updatedAppGW.OperationalState)" -ForegroundColor Green
# Save Gateway configuration
Write-Host "[$(__LINE__)] Attempting to save changes to the Application Gateway..." -ForegroundColor Cyan
Set-AzureRmApplicationGateway -ApplicationGateway $updatedAppGW | Out-Null
... gives the following console output:

Answer 1

OK, managed to fix the problem myself... sigh
On the Set-AzureRmApplicationGatewayRequestRoutingRule command, you must specify the -HttpListener parameter, or it will fail silently.
# Re-retrieve the Backend Address Pool and HTTP Settings that we've created, for the sake of updating the rule
$backendPool = Get-AzureRmApplicationGatewayBackendAddressPool -ApplicationGateway $AppGW -Name $MaintenanceToggleBackendPool
$httpSettings = Get-AzureRmApplicationGatewayBackendHttpSettings -ApplicationGateway $AppGW -Name $MaintenanceToggleHTTPSetting
$httpListener = Get-AzureRmApplicationGatewayHttpListener -ApplicationGateway $AppGW -Name "HttpListenerTest"
$updatedAppGW = Set-AzureRmApplicationGatewayRequestRoutingRule -ApplicationGateway $AppGW `
-Name $ChosenSubscription.httpsRule `
-RuleType Basic `
-BackendAddressPool $backendPool `
-BackendHttpSettings $httpSettings `
-HttpListener $httpListener
This is why the Set-AzureRmApplicationGateway command wasn't working properly - it had a malformed RequestRoutingRule in its memory.