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Before deploying a Bicep file, you can preview the changes that will happen. Azure Resource Manager provides the what-if operation to let you see how resources will change if you deploy the Bicep file. The what-if operation doesn't make any changes to existing resources. Instead, it predicts the changes if the specified Bicep file is deployed.
You can use the what-if operation with Azure PowerShell, Azure CLI, or REST API operations. What-if is supported for resource group, subscription, management group, and tenant level deployments.
During What-If operations, the evaluation and expansion of templateLink aren't supported. As a result, any resources deployed using template links within nested deployments, including template spec references, won't be visible in the What-If operation results.
If you would rather learn about the what-if operation through step-by-step guidance, see Preview Azure deployment changes by using what-if.
To deploy a Bicep file or ARM template, you need write access on the resources you're deploying and access to all operations on the Microsoft.Resources/deployments resource type. For example, to deploy a virtual machine, you need Microsoft.Compute/virtualMachines/write and Microsoft.Resources/deployments/* permissions. The what-if operation has the same permission requirements.
For a list of roles and permissions, see Azure built-in roles.
What-if expands nested templates until these limits are reached:
When one of the limits is reached, the remaining resources' change type is set to Ignore.
To use what-if in PowerShell, you must have version 4.2 or later of the Az module.
To install the module, use:
Install-Module -Name Az -Force
For more information about installing modules, see Install Azure PowerShell.
To use what-if in Azure CLI, you must have Azure CLI 2.14.0 or later. If needed, install the latest version of Azure CLI.
When you use what-if in PowerShell or Azure CLI, the output includes color-coded results that help you see the different types of changes.
The text output is:
Resource and property changes are indicated with these symbols:
- Delete
+ Create
~ Modify
The deployment will update the following scope:
Scope: /subscriptions/./resourceGroups/ExampleGroup
~ Microsoft.Network/virtualNetworks/vnet-001 [2018-10-01]
- tags.Owner: "Team A"
~ properties.addressSpace.addressPrefixes: [
- 0: "10.0.0.0/16"
+ 0: "10.0.0.0/15"
]
~ properties.subnets: [
- 0:
name: "subnet001"
properties.addressPrefix: "10.0.0.0/24"
]
Resource changes: 1 to modify.
Bilješka
The what-if operation can't resolve the reference function. Every time you set a property to a template expression that includes the reference function, what-if reports the property will change. This behavior happens because what-if compares the current value of the property (such as true or false for a boolean value) with the unresolved template expression. Obviously, these values will not match. When you deploy the Bicep file, the property will only change when the template expression resolves to a different value.
To preview changes before deploying a Bicep file, use New-AzResourceGroupDeployment or New-AzSubscriptionDeployment. Add the -Whatif switch parameter to the deployment command.
New-AzResourceGroupDeployment -Whatif for resource group deploymentsNew-AzSubscriptionDeployment -Whatif and New-AzDeployment -Whatif for subscription level deploymentsYou can use the -Confirm switch parameter to preview the changes and get prompted to continue with the deployment.
New-AzResourceGroupDeployment -Confirm for resource group deploymentsNew-AzSubscriptionDeployment -Confirm and New-AzDeployment -Confirm for subscription level deploymentsThe preceding commands return a text summary that you can manually inspect. To get an object that you can programmatically inspect for changes, use Get-AzResourceGroupDeploymentWhatIfResult or Get-AzSubscriptionDeploymentWhatIfResult.
$results = Get-AzResourceGroupDeploymentWhatIfResult for resource group deployments$results = Get-AzSubscriptionDeploymentWhatIfResult or $results = Get-AzDeploymentWhatIfResult for subscription level deploymentsTo preview changes before deploying a Bicep file, use:
You can use the --confirm-with-what-if switch (or its short form -c) to preview the changes and get prompted to continue with the deployment. Add this switch to:
For example, use az deployment group create --confirm-with-what-if or -c for resource group deployments.
The preceding commands return a text summary that you can manually inspect. To get a JSON object that you can programmatically inspect for changes, use the --no-pretty-print switch. For example, use az deployment group what-if --no-pretty-print for resource group deployments.
If you want to return the results without colors, open your Azure CLI configuration file. Set no_color to yes.
For REST API, use:
The what-if operation lists seven different types of changes:
FullResourcePayloads, which is the default value.sku.tier property is always set to match sku.name in the Microsoft.ServiceBus namespace.FullResourcePayloads, which is the default value.ResourceIdOnly.You control the level of detail that is returned about the predicted changes. You have two options:
The default value is FullResourcePayloads.
For PowerShell deployment commands, use the -WhatIfResultFormat parameter. In the programmatic object commands, use the ResultFormat parameter.
For Azure CLI, use the --result-format parameter.
The following results show the two different output formats:
Full resource payloads
Resource and property changes are indicated with these symbols:
- Delete
+ Create
~ Modify
The deployment will update the following scope:
Scope: /subscriptions/./resourceGroups/ExampleGroup
~ Microsoft.Network/virtualNetworks/vnet-001 [2018-10-01]
- tags.Owner: "Team A"
~ properties.addressSpace.addressPrefixes: [
- 0: "10.0.0.0/16"
+ 0: "10.0.0.0/15"
]
~ properties.subnets: [
- 0:
name: "subnet001"
properties.addressPrefix: "10.0.0.0/24"
]
Resource changes: 1 to modify.
Resource ID only
Resource and property changes are indicated with this symbol:
! Deploy
The deployment will update the following scope:
Scope: /subscriptions/./resourceGroups/ExampleGroup
! Microsoft.Network/virtualNetworks/vnet-001
Resource changes: 1 to deploy.
To see how what-if works, let's runs some tests. First, deploy a Bicep file that creates a virtual network. You'll use this virtual network to test how changes are reported by what-if. Download a copy of the Bicep file.
resource vnet 'Microsoft.Network/virtualNetworks@2023-11-01' = {
name: 'vnet-001'
location: resourceGroup().location
tags: {
CostCenter: '12345'
Owner: 'Team A'
}
properties: {
addressSpace: {
addressPrefixes: [
'10.0.0.0/16'
]
}
enableVmProtection: false
enableDdosProtection: false
subnets: [
{
name: 'subnet001'
properties: {
addressPrefix: '10.0.0.0/24'
}
}
{
name: 'subnet002'
properties: {
addressPrefix: '10.0.1.0/24'
}
}
]
}
}
To deploy the Bicep file, use:
New-AzResourceGroup `
-Name ExampleGroup `
-Location centralus
New-AzResourceGroupDeployment `
-ResourceGroupName ExampleGroup `
-TemplateFile "what-if-before.bicep"
After the deployment completes, you're ready to test the what-if operation. This time you deploy a Bicep file that changes the virtual network. It's missing one of the original tags, a subnet has been removed, and the address prefix has changed. Download a copy of the Bicep file.
resource vnet 'Microsoft.Network/virtualNetworks@2023-11-01' = {
name: 'vnet-001'
location: resourceGroup().location
tags: {
CostCenter: '12345'
}
properties: {
addressSpace: {
addressPrefixes: [
'10.0.0.0/15'
]
}
enableVmProtection: false
enableDdosProtection: false
subnets: [
{
name: 'subnet002'
properties: {
addressPrefix: '10.0.1.0/24'
}
}
]
}
}
To view the changes, use:
New-AzResourceGroupDeployment `
-Whatif `
-ResourceGroupName ExampleGroup `
-TemplateFile "what-if-after.bicep"
The what-if output appears similar to:
The text output is:
Resource and property changes are indicated with these symbols:
- Delete
+ Create
~ Modify
The deployment will update the following scope:
Scope: /subscriptions/./resourceGroups/ExampleGroup
~ Microsoft.Network/virtualNetworks/vnet-001 [2018-10-01]
- tags.Owner: "Team A"
+ properties.enableVmProtection: false
~ properties.addressSpace.addressPrefixes: [
- 0: "10.0.0.0/16"
+ 0: "10.0.0.0/15"
]
~ properties.subnets: [
- 0:
name: "subnet001"
properties.addressPrefix: "10.0.0.0/24"
]
Resource changes: 1 to modify.
Notice at the top of the output that colors are defined to indicate the type of changes.
At the bottom of the output, it shows the tag Owner was deleted. The address prefix changed from 10.0.0.0/16 to 10.0.0.0/15. The subnet named subnet001 was deleted. Remember these changes weren't deployed. You see a preview of the changes that will happen if you deploy the Bicep file.
Some of the properties that are listed as deleted won't actually change. Properties can be incorrectly reported as deleted when they aren't in the Bicep file, but are automatically set during deployment as default values. This result is considered "noise" in the what-if response. The final deployed resource will have the values set for the properties. As the what-if operation matures, these properties will be filtered out of the result.
Now, let's programmatically evaluate the what-if results by setting the command to a variable.
$results = Get-AzResourceGroupDeploymentWhatIfResult `
-ResourceGroupName ExampleGroup `
--template-file "what-if-after.bicep"
You can see a summary of each change.
foreach ($change in $results.Changes)
{
$change.Delta
}
To preview changes before deploying a Bicep file, use the confirm switch parameter with the deployment command. If the changes are as you expected, respond that you want the deployment to complete.
New-AzResourceGroupDeployment `
-ResourceGroupName ExampleGroup `
-Confirm `
-TemplateFile "what-if-after.bicep"
The text output is:
Resource and property changes are indicated with these symbols:
- Delete
+ Create
~ Modify
The deployment will update the following scope:
Scope: /subscriptions/./resourceGroups/ExampleGroup
~ Microsoft.Network/virtualNetworks/vnet-001 [2018-10-01]
- tags.Owner: "Team A"
+ properties.enableVmProtection: false
~ properties.addressSpace.addressPrefixes: [
- 0: "10.0.0.0/16"
+ 0: "10.0.0.0/15"
]
~ properties.subnets: [
- 0:
name: "subnet001"
properties.addressPrefix: "10.0.0.0/24"
]
Resource changes: 1 to modify.
Are you sure you want to execute the deployment?
[Y] Yes [A] Yes to All [N] No [L] No to All [S] Suspend [?] Help (default is "Y"):
You see the expected changes and can confirm that you want the deployment to run.
When you no longer need the example resources, use Azure CLI or Azure PowerShell to delete the resource group.
az group delete --name ExampleGroup
You can use the what-if operation through the Azure SDKs.
For Python, use what-if.
For Java, use DeploymentWhatIf Class.
For .NET, use DeploymentWhatIf Class.
Obučavanje
Modul
Preview Azure deployment changes by using what-if - Training
Apply the what-if command to see the effect of a deployment before it's applied.
Certifikacija
Microsoft Certified: Azure Developer Associate - Certifications
Build end-to-end solutions in Microsoft Azure to create Azure Functions, implement and manage web apps, develop solutions utilizing Azure storage, and more.
Dokumentacija
Deploy Bicep files with the Azure CLI - Azure Resource Manager
Learn how to use Azure Resource Manager and the Azure CLI to deploy resources to Azure. The resources are defined in a Bicep file.
Use Bicep to deploy resources to resource groups - Azure Resource Manager
Describes how to deploy resources in a Bicep file. It shows how to target more than one resource group.
Bicep CLI commands - Azure Resource Manager
Learn about the commands that you can use in the Bicep CLI. These commands include building JSON Azure Resource Manager templates from Bicep.