Managing Cross-Resource Dependencies | Azure ARM Tutorial

Welcome to the tutorial on managing cross-resource dependencies in ARM templates for Azure Resource Manager. ARM templates provide a powerful way to define and deploy infrastructure and applications in Azure. By managing dependencies between resources, you can ensure that resources are provisioned in the correct order and properly configured.

1. Defining Dependencies

In ARM templates, dependencies are defined using the dependsOn property within a resource's definition. The dependsOn property specifies the list of resources that the current resource depends on.


"resources": [
  {
    "type": "Microsoft.Storage/storageAccounts",
    "name": "myStorageAccount",
    "apiVersion": "2021-04-01",
    ...
  },
  {
    "type": "Microsoft.Compute/virtualMachines",
    "name": "myVM",
    "apiVersion": "2021-03-01",
    "dependsOn": [
      "Microsoft.Storage/storageAccounts/myStorageAccount"
    ],
    ...
  }
]

2. Managing Dependencies

To manage cross-resource dependencies effectively, follow these steps:

Step 1: Identify Dependencies

Identify the dependencies between resources in your deployment. Determine which resources need to be provisioned before others to ensure proper configuration and functionality.

Step 2: Define Dependencies

Within your ARM template, specify the dependsOn property for each resource that has a dependency. List the fully qualified resource IDs that the current resource depends on.


"resources": [
  {
    "type": "Microsoft.Compute/virtualMachines",
    "name": "myVM",
    "apiVersion": "2021-03-01",
    "dependsOn": [
      "Microsoft.Storage/storageAccounts/myStorageAccount"
    ],
    ...
  }
]

Step 3: Ensure Correct Order

Verify that the dependencies are defined in the correct order. Resources with dependencies should be listed after the resources they depend on.


"resources": [
  {
    "type": "Microsoft.Storage/storageAccounts",
    "name": "myStorageAccount",
    "apiVersion": "2021-04-01",
    ...
  },
  {
    "type": "Microsoft.Compute/virtualMachines",
    "name": "myVM",
    "apiVersion": "2021-03-01",
    "dependsOn": [
      "Microsoft.Storage/storageAccounts/myStorageAccount"
    ],
    ...
  }
]

Mistakes to Avoid

Missing or incorrect usage of the dependsOn property for resource dependencies.
Not considering the correct order of resource creation and their interdependencies when defining dependencies.
Not accounting for dependencies between resources in different resource groups or subscriptions.

Frequently Asked Questions (FAQs)

Q: Can I have circular dependencies between resources in ARM templates?
A: No, circular dependencies are not supported in ARM templates. You need to ensure that your template dependencies do not create circular references.
Q: Can I have dependencies across resource groups or subscriptions?
A: Yes, dependencies can be established across resource groups and subscriptions. Ensure that you have the necessary permissions and access rights to the target resources.
Q: How do I handle dependencies for resources that are conditionally deployed?
A: If a resource is conditionally deployed using the condition property, you should include the resource's dependency in the dependsOn list only when the condition is met.
Q: Can I use expressions or functions to define dependencies?
A: No, dependencies in ARM templates are defined using the dependsOn property, and it does not support expressions or functions. Dependencies are based on the resource IDs.
Q: What happens if a resource's dependency is not yet provisioned?
A: ARM templates handle dependencies automatically by ensuring that resources are provisioned in the correct order. If a resource's dependency is not yet provisioned, the deployment will wait until the dependency is created.

Summary

In this tutorial, you learned how to manage cross-resource dependencies in ARM templates for Azure Resource Manager. By defining dependencies using the dependsOn property, you can ensure that resources are provisioned in the correct order and properly configured. By managing dependencies effectively, you can create more robust and reliable deployments in Azure.