Virtual machine models
As you may recall from earlier in this book, there are two models for working with many Azure resources: Azure Resource Manager (ARM) and Azure Service Management (often referred to as the classic model or ASM). It is recommended that you use the Resource Manager model for new deployments. The classic model is still supported; however, the newest innovations will be made available only for the Resource Manager model.
For the purposes of this chapter, both models are covered, but the emphasis is on the Resource Manager model.
There are significant and fundamental differences in working with Azure Virtual Machines in these models.
Azure Resource Manager model
When working with the Resource Manager model, you have explicit and fine-grained control over nearly all aspects of the Azure VM. You will explicitly add components such as a network interface card (NIC), public IP address, data disks, load balancer, and much more.
You may recall that Resource Manager uses various resource providers to enable access to and management of Azure resources. There are three main resource providers used when working with Azure Virtual Machines: Network, Storage, and Compute.
The Network resource provider (Microsoft.Network) handles all aspects of network connectivity such as IP addresses, load balancers, NICs, and so on.
The Storage resource provider (Microsoft.Storage) handles the storage of the disks for a VM (in the context of Azure Virtual Machines).
The Compute resource provider (Microsoft.Compute) handles details related to the VM itself, such as naming, operating system details, and configuration (size, number of disks, and so on).
In addition to explicit control over the virtual machine’s components, you have the ability to take advantage of other Resource Manager features, such as:
Deployment and management of related resources as part of a resource group
Tags to logically organize and identify resources
Role Based Access Control (RBAC) to apply necessary security and control policies
Declarative template files
Deployment policies to enforce specific organizational rules
Consistent, orchestrated deployment process
Classic/Azure Service Management model
In the classic deployment model, VM deployments are always in the context of an Azure cloud service—a container for VMs. The container provides several key features, including a DNS endpoint, network connectivity (including from the public Internet if desired), security, and a unit of management. While you get these things for free—because they’re inherited from the cloud service model—you have limited control over them.
Use of the classic model also excludes the use of the additional value adding features available via Azure Resource Manager (tags, template files, and so on).
Source of Information : Microsoft Azure Essentials Fundamentals of Azure Second Edition