Getting Started with Templates for Azure Infrastructure as Code

Introduction

In the world of cloud computing, automating resource deployment and management is critical. Microsoft Azure’s ARM (Azure Resource Manager) Templates provide a way to define your cloud infrastructure in code, ensuring consistency, speed, and version control in your deployments. ARM Templates use JSON syntax to describe Azure resources, enabling you to deploy, update, or delete any Azure resource consistently.

In this blog, we’ll cover:

• What ARM Templates are
• Why you should use them
• Key components of an ARM Template
• Steps to create and deploy ARM Templates
• Best practices for using ARM Templates effectively

What is an ARM Template?

An ARM Template is a JSON file that defines the configuration and deployment of resources in Azure. The template file contains the infrastructure you need, such as virtual machines, storage accounts, databases, or networking components. ARM Templates are declarative, meaning you define the “what” instead of the “how” in your infrastructure setup.

With ARM Templates, you can deploy the same environment multiple times with consistency, making it ideal for DevOps and CI/CD practices.

Why Use ARM Templates?

Using ARM Templates provides many benefits:

1. Consistency: Every deployment is identical, reducing the risk of configuration drift.
2. Reusability: Once you create an ARM Template, you can reuse it for similar environments.
3. Version Control: ARM Templates can be stored in repositories like GitHub, allowing you to track changes.
4. Parameterization: Customize templates for different environments (e.g., dev, test, production) with parameters.
5. Automated Provisioning: Use templates in CI/CD pipelines to automate deployments.
6. Orchestration: Easy orchestration.

What are ARM Template Deployment Modes?

ARM Template deployment modes control how Azure handles resources in a target resource group during a deployment. Depending on the mode selected, resources not defined in the template may either be left untouched or deleted, impacting the overall configuration of your environment.

The two modes are:

1. Incremental Mode
2. Complete Mode

Incremental Deployment Mode

This mode is the by default used mode for ARM Templates. When you deploy in incremental mode, Azure adds or updates resources specified in the template without affecting any other existing resources in the resource group. This mode is ideal for scenarios where you want to deploy additional resources or update existing ones without making unintended changes.

Complete Deployment Mode

Complete mode offers a more rigid deployment approach, ensuring that the resource group matches exactly what’s defined in the ARM Template. In this mode, Azure removes any resources in the target resource group that are not specified in the template, effectively making the environment a mirror of the template definition.

Key Components of an ARM Template

An ARM Template schema:

1. $schema: Defines the location of the JSON schema for validating the template.
2. contentVersion: Specifies the version of the template content.
3. parameters: Allows you to pass values into the template to make it flexible.
4. variables: Stores values that remain constant, like resource names or locations.
5. resources: Describes the Azure resources you want to deploy or manage, such as virtual machines, storage, or databases.
6. outputs: Specifies the values returned after deployment, such as connection strings or resource IDs.

Here’s a basic template structure:

{

“$schema”: “https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#”,

“contentVersion”: “1.0.0.0”,

“parameters”: {},

“variables”: {},

“resources”: [],

“outputs”: {}

}

Best Practices for ARM Templates

1. Use Parameters for Flexibility: Parameterize values like names, locations, and SKU sizes so that the template is reusable in different environments.
2. Leverage Variables for Repeated Values: If you’re using the same value in multiple places, store it in a variable.
3. Use Outputs to Return Key Information: Define outputs to retrieve important information, like connection strings or resource IDs.
4. Structure Templates Modularly: Break down complex templates into smaller ones and link them using linked templates for easier management.
5. Version Control and Documentation: Store templates in a repository and document them, especially the parameters, to improve collaboration.

What is Bicep?

Bicep is a domain-specific language (DSL) developed by Microsoft to simplify Azure resource deployments. It’s designed to make writing IaC for Azure more readable and manageable than JSON-based ARM Templates. Bicep is a transpiler, meaning it compiles to ARM Template JSON under the hood. Bicep’s syntax is cleaner and more concise, making it ideal for those looking for a more straightforward IaC experience.

Key Features of Bicep:

• Simplified syntax: Bicep is much more readable and compact than JSON.
• Reusable modules: Bicep supports modularity, allowing you to split code into reusable components.
• Direct ARM integration: Compiles to ARM JSON, so it’s fully compatible with existing Azure services.
• Rich tool support: VS Code extension and IntelliSense support for easier authoring and validation.

Key Differences Between ARM Templates and Bicep

When to Use ARM Templates vs. Bicep

• Use ARM Templates if:
  • You have a complex environment already defined in JSON and want to continue managing it without migrating.
  • You’re deploying using legacy systems or tools that require JSON-based templates.
  • You need direct JSON compatibility for backward compatibility with specific Azure tools or configurations.
• Use Bicep if:
  • You’re starting fresh with Azure IaC and want an easier-to-learn, more readable syntax.
  • You prefer modular, maintainable code and anticipate needing reusable components.
  • You want a streamlined, compact IaC experience without the verbosity of JSON.

Conclusion

Both ARM Templates and Bicep are powerful tools for deploying Azure resources. While ARM Templates offer robust, long-standing support in Azure, Bicep brings a more modern, concise approach to IaC. For developers who value readability, modularity, and ease of use, Bicep may be the best choice. However, for those who prefer JSON-based definitions or need maximum compatibility with legacy systems, ARM Templates remain a strong option.

Azure developers now have a choice between these tools to match their project needs, preferences, and deployment styles. Embrace the tool that best aligns with your goals and see the benefits of IaC in your Azure environment!

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