“The provided value for the template parameter is not valid” in ARM template deployments

I’ve come across this one before, but I hit it again today and I wanted to share the details of what happened. Basically the scenario is this, I have an ARM template that I want to deploy and it takes in parameters. The deployment needs to run through PowerShell using the Azure RM PowerShell cmdlets. When I call New-AzureRmResourceGroupDeployment I get the error that says “The provided value for the template parameter is {parameter name} not valid”, and this is where things start getting weird.

Here is an example of how I was calling it:

New-AzureRmResourceGroupDeployment -ResourceGroupName "MyRGName" `
                                   -Name "MyDeployment" `
                                   -TemplateUri "http://url.of/MyTemplate.json" `
                                   -TemplateParameterObject @{
                                       Parameter1 = "Value"
                                       Parameter2 = "Other value"

Now what you’re looking at here is perfectly valid PowerShell – it gets parsed by the engine, compiled and executed as you would expect it to, but for some reason I was getting the error about Parameter1 not being a valid value. This error typically comes up where there is a data type mismatch or some other type of parameter validation error – such as asking for a string in the template but you give it a number, or you didn’t provide a mandatory value, or those sorts of things. But in my case, none of that was true – the data type was a string and there was a value and that’s all there was to it. I even put the parameter values in to an external file and ran that, and that worked! So I knew there was no issue with the value I was providing, so I had to figure out why it wouldn’t accept it in the format I was providing. I started trying things, I tried taking the hashtable out in to a separate variable and that didn’t seem to help – but then I found another way of calling things that seemed to do the trick:

$params = @{}
$params.Add("Parameter1", "Value")
$params.Add("Parameter2", "Other value")

New-AzureRmResourceGroupDeployment -ResourceGroupName "MyRGName" `
                                   -Name "MyDeployment" `
                                   -TemplateUri "http://url.of/MyTemplate.json" `
                                   -TemplateParameterObject $params


For those not familiar, the first line of that example is creating a new and empty hashtable (it’s the equivalent of running ‘New-Object -TypeName System.Collections.Hashtable’). From there I call the .Add() method to add each item to the hashtable rather than doing it inline like I was doing in the first example. Now I’ve done this both ways in separate PowerShell windows and I absolutely cannot for the life of me pick a difference between a hashtable declared in the first example and the second one. They are the same object time, they compare the same, they have the same keys and values … and yet for some reason when I pass the second example in to the Azure RM cmdlets it works, while the first is clearly losing the value somewhere along the way.

So I don’t have an explanation on the “why” in this case, but I can tell you that the second example works where the first one doesn’t. I’ve observed this behavior from both my laptop when I run cmdlets, as well as in Azure Automation when I try to do a deployment from a runbook as well, so look out for it anywhere the RM cmdlets run. I hope this helps other people get around this one if you come up against it!

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