Understanding Child Resources in Bicep

In Azure, certain resources are related to or attached to other resources, such as containers within a storage account. These are known as child resources. Defining child resources in a Bicep template can be done in two ways: nested and parent. Each method has its use cases and benefits, which we will explore in this post.

Nested Resources

Nested resources are defined directly within the parent resource's definition. This approach is straightforward and keeps the related resources encapsulated within the main resource. Here's an example:

// Definition of the main resource
resource sa 'Microsoft.Storage/storageAccounts@2023-05-01' = {
  name: 'myStorageAccount'
  location: resourceGroup().location
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
  
  // Nested resource: Blob service within the storage account
  resource blobservice 'blobServices@2023-05-01' = {
    name: 'default'

    // Nested resource: Blob container within the blob service
    resource container 'containers@2023-05-01' = {
      name: 'myContainer'
    }
  }
}

In this example, the blobservice resource is nested within the sa (storage account) resource, and the container resource is further nested within the blobservice resource. This nested structure clearly indicates the hierarchical relationship between the resources.

Parent Resources

Alternatively, child resources can be defined using the parent property. This method establishes the relationship between resources by explicitly specifying the parent resource. Here’s how it looks:

// Definition of the main resource: Storage account
resource sa 'Microsoft.Storage/storageAccounts@2023-05-01' = {
  name: 'myStorageAccount'
  location: resourceGroup().location
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
}

// Definition of the blob service resource within the storage account
resource blobservice 'Microsoft.Storage/storageAccounts/blobServices@2023-05-01' = {
  // Establishing the relationship with the storage account
  parent: sa
  name: 'default'
}

// Definition of the blob container resource within the blob service
resource container 'Microsoft.Storage/storageAccounts/blobServices/containers@2023-05-01' = {
  // Establishing the relationship with the blob service
  parent: blobservice
  name: 'myContainer'
}

In this example, the blobservice resource specifies sa as its parent, and the container resource specifies blobservice as its parent. This approach makes it clear which resources are related to each other through the parent property.

The Choice

The choice between using nested resources or parent resources in Bicep largely depends on your preference and the complexity of your resource relationships. Nested resources can make the template more concise and easier to read when dealing with simple hierarchies. On the other hand, using the parent property can make the relationships explicit and more flexible, especially in complex deployments where resources might need to be referenced in various places within the template.

Both methods are valid and can be used interchangeably based on the requirements of your Azure infrastructure deployment.

I hope this clarifies the concept of child resources in Bicep and helps you choose the best method for your deployments. If you have any questions or need further assistance, feel free to reach out!

Happy coding!