What is Azure Resource Manager (ARM) and how does it differ from the classic deployment model?

Azure Resource Manager (ARM) is the deployment and management service for Azure. It provides a consistent management layer that enables you to create, update, and delete resources in your Azure subscription using infrastructure as code.

ARM vs Classic Deployment Model

The Classic deployment model (also called Azure Service Manager or ASM) was the original Azure deployment system. It treated resources individually and lacked the ability to manage them as a group. ARM replaced it with a resource-group-based approach.

Key differences: In ARM, resources are organized into Resource Groups – logical containers for resources that share the same lifecycle. Classic had no resource grouping. ARM enables declarative templates (ARM templates or Bicep) to define infrastructure. Classic required scripting each resource individually. ARM supports role-based access control (RBAC) at the resource, resource group, or subscription level. Classic had limited access controls. ARM tracks dependencies between resources and deploys them in the correct order. ARM supports tags on resources for cost tracking and organization.

ARM Templates

ARM templates are JSON files that define the infrastructure and configuration for your project. They follow an idempotent deployment model where you define the desired state and ARM ensures the environment matches. Bicep is a domain-specific language (DSL) that compiles to ARM templates and provides cleaner syntax.

Resource Groups

A resource group is a logical container where Azure resources are deployed and managed. All resources in a group share the same lifecycle – you can deploy, update, or delete them together. Resources in the same group can be in different regions. Resource groups enable cost management and access control at a group level.