PowerShell DSC Journey – Day 17

Alright. So yesterday I worked through some issues in the Set-TargetResource Function and left off with a big one still remaining. Namely, that even though I have Ensure = Present in my test of the Function, it is running through the Ensure = Absent portion of the script if the Hardware Profile already exists, which doesn’t make any sense.

Here is the section of the Function in question.

And if I run this Test with a Hardware Profile that already exists, this is the output that I get.

And I know it’s removing it because the Hardware Profile disappears from VMM. The question is, why? I can see from the Verbose output that $Ensure is set to Present, so why is the Function ignoring that? As another test, if I run the same test but set $Ensure to Absent, it removes it. But that was really just a diversion to avoid thinking about the real problem because I am completely stumped.

I change my Else block to ElseIf($Ensure = “Present”) and that has no effect. It just jumps right into the If Absent block and deleted the Hardware Profile. Lacking ideas I start going through the xVMHyperV Set-TargetResource function searching for Ensure to see how they do it. And they are using -eq in the If statement instead of =. Does this really make a difference? Yes, that’s the answer. After I change it to that, it evaluates the parameter properly. I feel like this is a very simple mistake that I made solely because of my lack of experience and knowledge of PowerShell.

Doing a little research in PowerShell using Get-Help I discover the following:

  • = is an Assignment Operator.  It sets the value of a variable to a specified value
  • -eq is a Comparison Operator.  It compares to objects looking for an identical value
  • Thus, = does not equal -eq.  I feel dumb.  I should have known that.

That being said, when I run my test using an existing Hardware Profile now (with Ensure = Present), I get this for output.

Clearly there are a couple of issues here. The DVDDrive section looks OK, but then in the CPU section I get this beauty for Verbose output.

Yeah, that’s not real useful. Looking at this it appears that $HWProfile.CPCount is not what I think it is. Actually I think it’s because I used $HWProfile instead of the $ResourceHWProfile variable. This is going to require a fix in a lot of places. I make those changes and try my test again. I get the expected output, except that I get the same error about the VirtualNetworkAdapter that I got above. This goes back to my work in the previous blog post about how to handle this, because I don’t want to make this parameter mandatory. So, I need to add in some additional logic to my Function here.

And now when I run my test, I get exactly the output that I would expect.

I do various tests with different CPU, DVDDrive and VMNetwork settings and everything looks good. I do make a change to one line of Verbose output, but other than that everything checks out fine. This is really cool. I have an actual functioning DSC Custom Resource. Tomorrow I am going to turn this thing into a Module, and try out an actual DSC Configuration and see if that actually works before adding in my additional parameters.