Friday, August 15, 2014

Getting errors from the Azure VM custom script extension without RDP

Since Azure has begun adding the VM agent and other extension to IaaS virtual machines (persistent VM Roles) a number of scenarios and possibilities have opened up.

The extension is a simple binary that is dropped into your VM and built to be triggered and to perform very specific actions in the security context of Local System.

The Desired State Configuration Azure extension is the very latest. 

Prior to this I have been spending some time with the Custom Script Extension.  And it is rather nifty.  But the biggest pain that I have had is in working through the process of troubleshooting the script as I develop it.

I have found no way to capture the standard output - other than directing to a text file.  But then I have to RDP into the VM to fetch it.

I can also look at the runtime status of the extension while connected over RDP - that that is one file with bad line endings, making it difficult to read in Notepad.

Trough a bit of searching I came across a few tips and started poking around a bit with the Azure PowerShell cmdlets. 

What I discovered is that you cannot get the standard output, but you can get the standard error through the API.  So, if the script tosses some terminating error, there is output to be fetched. If there was no error, there is no output to be returned.

What I ended up doing is the following:

New-AzureVM -Location $location -VM $vmConfig -ServiceName $Service

(Get-Date -Format s) + " .. Watch the script extionsion to monitor the deployment and configuration"
Do {
    $Vm = Get-AzureVM -Name $vmName -ServiceName $Service

    Get-Date -Format s
    "  Machine status: " + $Vm.Status
    "  Guest agent status: " + $Vm.GuestAgentStatus.FormattedMessage.Message
    foreach ( $extension in $Vm.ResourceExtensionStatusList ) {
        If ( $extension.HandlerName -match 'CustomScriptExtension' ) {
            "  ExtensionStatus: " + $extension.ExtensionSettingStatus.FormattedMessage.Message
            $scriptStatus = $extension.ExtensionSettingStatus.FormattedMessage.Message
            $scriptError = foreach ($substatus in $extension.ExtensionSettingStatus.SubStatusList) { ($substatus.FormattedMessage.Message).Replace("\n","`n") }
    Start-Sleep 10
} until ( ($scriptStatus -eq "Finished executing command") )

I fetch the VM, then drill into the object for the Custom Script Extension, then I dig into the Extension status, and it even has sub status.  It is in this sub status where the Standard Error ends up being bubbled up for the extension.

I realize that this leaves me waiting around and calling back and forth.  But a green light on "Finished executing command" only means the script extension is completed running whatever I told it to run, not that it worked.

I just wish I could get the standard output.



Gaurav said...

Hi Brian,

I also need the output from custom script extension and I was able to get it to some extent.. yes off-course it was not in so readable form.Not sure if you have tried below links :


BrianEh said...

Yes. I began with those. Thanks for referencing them!