Azure Virtual Machines (VMs) let you create and use virtual machines in the cloud.
They provide infrastructure as a service (IaaS).

You can create and provision a VM in minutes when you select a pre-configured VM image.

An image is a template used to create a VM. These templates already include an OS and often other software, like development tools or web hosting environments.

When to use virtual machines?

• During testing and development
• When running applications in the cloud.
• When extending your datacenter to the cloud.
• During disaster recovery.

Scaling VMs in Azure

• Availability sets
• Virtual Machine Scale Sets
• Azure Batch

Availability sets

VMs are put into different update domains. Update domains indicate groups of VMs and underlying physical hardware that can be rebooted at the same time. Update domains are a logical part of each data center and are implemented with software and logic.

The group of virtual machines that share common hardware are in the same fault domain. A fault domain is essentially a rack of servers. It provides the physical separation of your workload across different power, cooling, and network hardware that support the physical servers in the data center server racks. In the event the hardware that supports a server rack becomes unavailable, only that rack of servers is affected by the outage.

The group of virtual machines that share common hardware are in the same fault domain.

A planned maintenance event is when the underlying Azure fabric that hosts VMs is updated by Microsoft. A planned maintenance event is done to patch security vulnerabilities, improve performance, and add or update features.

Unplanned maintenance events involve a hardware failure in the data center, such as a power outage or disk failure. VMs that are part of an availability set automatically switch to a working physical server so the VM continues to run.

With an availability set, you get:

• Up to three fault domains that each have a server rack with dedicated power and network resources
• Five logical update domains which then can be increased to a maximum of 20

Virtual machine scale sets

Azure Virtual Machine Scale Sets let you create and manage a group of identical, load balanced VMs.
Scale sets allow you to centrally manage, configure, and update a large number of VMs in minutes to provide highly available applications.
The number of VM instances can automatically increase or decrease in response to demand or a defined schedule

Azure Batch

Azure Batch enables large-scale job scheduling and compute management with the ability to scale to tens, hundreds, or thousands of VMs.

When you're ready to run a job, Batch does the following:

• Starts a pool of compute VMs for you
• Installs applications and staging data
• Runs jobs with as many tasks as you have
• Identifies failures
• Requeues work
• Scales down the pool as work completes