Azure Bicep Inheritance: Global & Module Tags Workaround

Inheritance is not natively supported in Azure Bicep, but with the creative use of modules and functions like union, we can implement a similar behavior.

This article demonstrates a practical workaround to manage global tags and extend them with module-specific tags dynamically.

The example includes creating two modules.

Storage Account
Log Analytics Workspace

These modules receive and process tags via a centralized Tags module.

Problem Statement

Azure resources often require consistent tagging for governance, cost management, and resource tracking. While global tags can be applied at a subscription or resource group level, module-specific tags might still be needed. Combining these efficiently within the Bicep can be challenging.

Objective

Create a centralized Tags module to handle global tags and allow extension with module-specific tags.
Use the union function to combine global and module-specific tags dynamically.
Demonstrate the implementation of a Storage Account and Log Analytics Workspace.

Features of Azure Bicep function Union

Returns a single array or object with all elements from the parameters.
For arrays, duplicate values are included once.
For objects, duplicate property names are only included once.
The union function merges not only the top-level elements but also recursively merges any nested objects within them. Nested array values are not merged.

Ref: https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/bicep-functions-array#union

Solution Design

Solution Design

1. Tags Module

File: modules/tags.bicep

This module accepts the below params.

global tags
module-specific tags

Returns a new object by combining both the global tags and the module-specific tags using the Bicep function union.

param globalTags object
param moduleTags object = {}
var combinedTags = union(globalTags, moduleTags)
output tags object = combinedTags

2. Storage Account Module

File: modules/storage.bicep

This module demonstrates applying tags to a Storage Account resource.

param storageAccountName string
param location string
param tags object

resource storageAccount 'Microsoft.Storage/storageAccounts@2022-09-01' = {
  name: storageAccountName
  location: location
  kind: 'StorageV2'
  sku: {
    name: 'Standard_LRS'
  }
  tags: tags
}

3. Log Analytics Workspace Module

File: modules/loganalytics.bicep

This module applies tags to a Log Analytics Workspace resource.

param workspaceName string
param location string
param tags object
resource logAnalyticsWorkspace 'Microsoft.OperationalInsights/workspaces@2023-03-01' = {
  name: workspaceName
  location: location
  sku: {
    name: 'PerGB2018'
  }
  tags: tags
}
output workspaceId string = logAnalyticsWorkspace.id

4. Main Bicep File

File: main.bicep

The main file integrates all modules and demonstrates the inheritance mechanism by combining global tags with module-specific tags.

// Global tags
var globalTags = {
  environment: 'Production',
  owner: 'TeamA'
}

// Module-specific tags
var storageTags = {
  moduleType: 'StorageAccount'
}

var logAnalyticsTags = {
  moduleType: 'LogAnalyticsWorkspace'
}

// Tags for Storage Account
module tagsStorage 'modules/tags.bicep' = {
  name: 'tagsStorage'
  params: {
    globalTags: globalTags
    moduleTags: storageTags
  }
}

// Deploy Storage Account
module storage 'modules/storage.bicep' = {
  name: 'storageAccount'
  params: {
    storageAccountName: 'prodstorage001'
    location: 'eastus'
    tags: tagsStorage.outputs.tags
  }
}

// Tags for Log Analytics Workspace
module tagsLogAnalytics 'modules/tags.bicep' = {
  name: 'tagsLogAnalytics'
  params: {
    globalTags: globalTags
    moduleTags: logAnalyticsTags
  }
}

// Deploy Log Analytics Workspace
module logAnalytics 'modules/loganalytics.bicep' = {
  name: 'logAnalyticsWorkspace'
  params: {
    workspaceName: 'prodloganalytics001'
    location: 'eastus'
    tags: tagsLogAnalytics.outputs.tags
  }
}

After running the bicep code, below is how the tags are created in Storage and the Log Analytics Workspace.

Storage Account Tags

Storage Account Tags

Log Analytics Workspace

Log Analytics Workspace

Explanation

Tags Module: Combines global and module-specific tags using the union function.
Storage and Log Analytics Modules: Create each Azure resource and also use the combined tags as inputs for resource creation.
Main File: Demonstrates tag inheritance by passing global tags to the Tags module and dynamically adding a module type tag.

Benefits

Centralized tag management simplifies governance.
Flexible design allows module-specific customization without duplicating global tags.
Scalable for additional modules.

Summary

This article provides a practical approach to implementing inheritance-like behavior in Azure Bicep by leveraging the union function for tag management. The solution centralizes global tags and allows dynamic extension with module-specific tags. By combining these efficiently, we achieve a scalable, maintainable, and consistent tagging strategy across different Azure resources.