Start-DscConfiguration doesn't throw exceptions? - powershell

Question

I noticed that if applying a configuration through Start-DscConfiguration fails, it writes to the error stream but doesn't
throw an Exception? That is, if I do the following:
try{
Start-DscConfiguration -Path ".\MyConfig" -Wait -Verbose
}catch{
#...
}
...it never ends up in the catch handler. I suspect this may have something to do with the fact that without the "-Wait",
Start-DscConfiguration starts an async job for this, and async commands probably don't throw exceptions, but in a synchronous
scenario, I would very much like to know if my configuration could be applied.
What is the proper way to determine if Start-DscConfiguration has completed succesfully?

Answer 1

The only way I know is to check the global "$error" variable and compare the number of error records before and after your call to Start-DscConfiguration. If there's more afterwards then something must have gone wrong during the call, so throw your own exception:
Configuration TestErrorHandling {
Node "localhost" {
Script ErroringResource {
GetScript = { return $null; }
TestScript = { return $false; }
SetScript = { throw new-object System.InvalidOperationException; }
}
}
}
$errorCount = $error.Count;
write-host "starting dsc configuration"
$mof = TestErrorHandling;
Start-DscConfiguration TestErrorHandling –Wait –Verbose;
write-host "dsc configuration finished"
if( $error.Count -gt $errorCount )
{
$dscErrors = $error[$errorCount..($error.Count - 1)];
write-host "the following errors occurred during dsc configuration";
write-host ($dscErrors | fl * | out-string);
throw $dscErrors[-1];
}

Answer 2

There's another way to make it cause an exception. Try saving it into the ErrorVariable like this :
try
{
Start-DscConfiguration -Path ".\MyConfig" -Wait -Verbose -ErrorVariable ev
}
catch
{
$myException = $_
}
Weirdly so, this throws the exception when there's an error (which is what you wanted). You can get the value of your exception in the $myexception variable, and also could get just a one liner description of your error using $ev
PS: Note that while mentioning ev in the errorVariable parameter, you do it without the '$' symbol - since you're only specifying the variable 'name'.

Answer 3

Start-DscConfiguration when used without -Wait will create a job object - with one child job for every computername. PowerShell job objects have an Error stream which contains all the errors. You can check this stream as well
$job = Start-DscConfiguration -Force -Verbose -Path C:\Temp\Demo\ -ComputerName localhost
Receive-Job $job -Wait
'Errors in job = ' + ($job.childjobs[0].Error.Count)