VIRTUAL MACHINE SCALE SETS (VMSS) AND AVAILABILITY SET
Tags: beginners, tutorial, cloud, azure
Published: 2022-11-04 17:47:19


A VMSS is a service offered by Azure that aids in the creation and management of several identical virtual machines. According to usage or a predetermined schedule, the number of VM instances can automatically increase or decrease.

**What are the Benefits of VMSS?**

- VMSS keeps your environment's configuration (VM size, disc configuration) uniform using the same basic OS image and parameters to produce all VM instances. This method frees you from additional configuration effort or network administration to manage hundreds of VMs. 



- It provides application resiliency and high availability. If ever one of the VM instances experiences an issue, Customers will still access your application through one of the other VM instances with little disruption.


- VMSS gives your application the ability to scale automatically as resource demand varies. Judging from your application’s customer demands, VM Scale Sets automatically increases or decreases the number of VM instances to match customer demand.


- Its auto scale ability to reduce the number of superfluous VM instances that run your application when demand is low enables cost-reduction while still giving customers performance satisfaction. 


**AVAILABILITY SETS** 

Availability set is a logical grouping of virtual machines (VMs) to help Azure comprehend how you created your application that is hosted on the virtual machines in order to provide redundancy and availability. In other words, it ensures that virtual machines are deployed across multiple isolated hardware nodes in a cluster to help manage maintenance updates and hardware problems so resources do not all go down at once. 


**How Does Availability Set Work?** 

Once two or more VMs are created within an availability set, each in your availability set is assigned an update domain and a fault domain by the underlying Azure platform.
 
The update domain is a collection of virtual computers that may be restarted or maintained simultaneously. System updates are ensured to be uninterrupted by the update domain. Each time an update domain is updated or restarted, it is given 30 minutes to recuperate before maintenance on another update domain is started.

Fault domains define the group of virtual machines that share a common power source and network switch. The virtual machines that are set up in your availability configuration by default are dispersed across up to three fault domains by Azure. This strategy lessens the effects of any hardware malfunctions, network attacks, or power outages.

**Differences Between VMSS AND Availability Set**

- VMSS is used for unpredictable work load while Availability set works for predictable work loads.  

- With VMSS, one can increase or decrease VMs based on demand while with Availability set, VMs can only be added upon creation. No modification or transfer can be made in and out of the set. 

- VMSS consist of identical configured VMs created and spread across domains while Availability set can consist of distinct VMs with unique properties and identity spanned across domains