Welcome to the ARM Template What-If issues repo

This repo is a little bit abnormal in that it is solely for keeping track of issues in the ARM Template what-if API. If you want to learn more about the what-if feature, you can take a look at this doc on the full capabilities of the what-if API and corresponding PowerShell cmdlet.

• ARM template deployment what-if operation (Preview)
• What's new in ARM Templates - November 2019 #MSIgnite Session (YouTube)

For a guided tutorial on What-If, check out this MS LEARN module.

Install PowerShell module

To use What-If in PowerShell, install a preview version of the Az.Resources module from the PowerShell gallery by running:

Install-Module Az.Resources -RequiredVersion 1.12.1-preview -AllowPrerelease

If you previously installed an alpha version of the what-if module, take the steps described in the ARM template deployment what-if operation (Preview) doc to uninstall that module.

What types of issues are you looking for?

The what-if issues fall into two buckets:

1. Noise in the diff: These are cases when what-if thinks a resource property will be changed (most often deleted) when in fact no change will occur. This is the primary motivation for this issue repo.
2. Issues with formatting or general usability of the cmdlet or API: There could be issues with formatting the diff, a parameter set may not be working correctly, etc.

Why does noise occur?

Often times, a property may be returned in a GET request for a resource that is not specified in the ARM template. The What-If API has a noise reduction service to catch these false positives and not return them. However, there are many cases where these could be missed. When this happens, it's likely that the what-if API will tell you that a resource will be modified and a specific property is deleted.

Let's look at an example.

Below is a storage account object declaration in an ARM Template, which is a little different than a pure REST API PUT body:

{
  "name": "storagedczol7xfovaoe",
  "type": "Microsoft.Storage/storageAccounts",
  "apiVersion": "2019-04-01",
  "sku": {
    "name": "Standard_LRS"
  },
  "kind": "Storage",
  "location": "eastus",
}

And here is only part of what the storage account looks like on GET. We've shortened in this readme, but you can see the full body here:

{
  "sku": {
    "name": "Standard_LRS",
    "tier": "Standard"
  },
  "kind": "Storage",
  "id": "/subscriptions/e93d3ee6-fac1-412f-92d6-bfb379e81af2/resourceGroups/test-005/providers/Microsoft.Storage/storageAccounts/storagedczol7xfovaoe",
  "name": "storagedczol7xfovaoe",
  "type": "Microsoft.Storage/storageAccounts",
  "location": "eastus",
  "tags": {},
  "properties": {
    "networkAcls": {
      "bypass": "AzureServices",
      "virtualNetworkRules": [],
      "ipRules": [],
      "defaultAction": "Allow"
    },
    "supportsHttpsTrafficOnly": true,
    ...
  }
}

In order to output a clean diff, we do post-processing on the diff to remove all of this noise, but there are many cases that have not yet been accounted for. If we run the same storage account creation through what-if, then we will see some of this noise:

How do I submit an issue?

In order to take an action on noise you encounter, please open an issue and include the following information:

1. Resource type (i.e. Microsoft.Storage/storageAccounts)
2. apiVersion (i.e. 2019-04-01)
3. Client (PowerShell, Azure CLI, API)
4. Relevant ARM Template code (we only need the resource object specified in 1 and 2, but if it's easier you can include the entire template
5. Expected response (i.e. "I expected no noise since the template has not been modified since the resources were deployed)
6. Current (noisy) response (either include a screenshot of the what-if output, or copy/paste the text)

Sample issue

You can see a sample issue for the above here. Hopefully it gets closed soon :)

Contributing

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This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.