A resource invocation that throws an exception can cause endless loop.

[alx9r]

Currently the config instructions enumerable does not catch exceptions that invoking a resource might throw. This can lead to an endless loop.

Repro

Running this code causes an endless loop.

$document = {
    Get-DscResource TestStub | Import-DscResource

    TestStub a @{
        Key = 'a'
        ThrowOnSet = 'always'
    }
}

$instructions = ConfigInstructions Name $document
$instructions |
    Invoke-ConfigStep

The above code results in an endless loop.

Solution

Exceptions thrown by resources should be caught, the resource marked as "failed" (or maybe "ExceptionThrown"), and then the exception re-thrown. If the resource is marked with a new value like "ExceptionThrown", the state machines should also be altered to raise and handle 'AtExceptionThrown' events.

[alx9r]

It seems like the .Invoke('Set') here should be wrapped in a try{} block.