ARM Template vs Bicep: Key Differences and When to Use Each

An ARM template is a JSON file used to define Azure resources declaratively, while Bicep is a newer, simpler language that compiles into ARM templates. Bicep offers easier syntax and better readability, making infrastructure code easier to write and maintain.

Quick Comparison

Here is a quick side-by-side comparison of ARM templates and Bicep for Azure infrastructure as code.

Factor	ARM Template	Bicep
Syntax	Verbose JSON	Concise, domain-specific language
Readability	Harder to read and write	Easier to read and write
Tooling	Supported by Azure tools	Built-in support with better tooling
Compilation	Direct deployment	Compiles to ARM JSON before deployment
Learning Curve	Steeper for beginners	Gentler for beginners
Modularity	Complex with nested templates	Simpler with modules and reuse

Key Differences

ARM templates use JSON format, which can be very detailed and verbose. This makes them harder to write and understand, especially for beginners or large projects. They require careful management of syntax like commas and brackets.

Bicep is a new language designed to simplify Azure infrastructure as code. It uses a clean, readable syntax that looks like a programming language instead of JSON. Bicep files compile into ARM templates, so they work with all Azure deployment tools.

Another key difference is tooling. Bicep has built-in support in Azure CLI and Visual Studio Code with features like syntax highlighting, autocompletion, and error checking. ARM templates have tooling too but are less user-friendly. Bicep also supports easier modularity, letting you reuse code with simple modules.

Code Comparison

Here is an example of creating an Azure Storage Account using an ARM template in JSON format.

json

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2021-04-01",
      "name": "examplestorageacct",
      "location": "eastus",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "StorageV2",
      "properties": {}
    }
  ]
}

Output

Deploys a Storage Account named 'examplestorageacct' in East US with Standard_LRS SKU.

Bicep Equivalent

The same Storage Account created with Bicep looks much simpler and easier to read.

bicep

resource storageAccount 'Microsoft.Storage/storageAccounts@2021-04-01' = {
  name: 'examplestorageacct'
  location: 'eastus'
  sku: {
    name: 'Standard_LRS'
  }
  kind: 'StorageV2'
  properties: {}
}

Output

Deploys a Storage Account named 'examplestorageacct' in East US with Standard_LRS SKU.

When to Use Which

Choose ARM templates if you need direct JSON control or are working with legacy projects already using them. They are also useful if you want to avoid an extra compilation step.

Choose Bicep when starting new Azure infrastructure projects for easier writing, better readability, and improved tooling support. Bicep reduces errors and speeds up development, making it ideal for beginners and teams wanting cleaner code.

Key Takeaways

Bicep is a simpler, more readable language that compiles into ARM templates.

ARM templates use verbose JSON and have a steeper learning curve.

Bicep offers better tooling and modularity for Azure infrastructure as code.

Use ARM templates for legacy or direct JSON needs; use Bicep for new projects.

Bicep improves productivity and reduces errors compared to ARM templates.