In-Depth Overview of Azure Availability Set

As with on-premises datacenters, planned maintenance operations and potential hardware faults also need to be considered when deploying resources over the cloud. A proper organization of virtual machines therefore becomes essential to avoid or minimize service disruption time. To that end, Microsoft Azure Availability Sets provide administrators the capability to group resources together in order to optimize the execution of maintenance tasks.

Definition of Azure Availability Set

When you deploy new virtual machines (VMs), Azure, by default, does not possess the necessary information to identify dependencies among them. Hence, this may lead to a single point of failure in the hosted service due to an unexpected hardware fault or a maintenance operation.

An Azure Availability Set is a logical grouping capability that guarantees that the VMs included in the same group are isolated from each other. Availability Sets are based on two logical groupings: fault domains and update domains. VMs included in the same fault domain share common power and network resources, similar to a rack at an on-premises datacenter. VMs belonging to the same update domain group can undergo both planned and unplanned maintenance, as well as simultaneous reboots. This configuration covers 99.95% of service-level agreements (SLAs).

A best practice when working with Availability Sets is to create one Availability Set per workload, understanding the workload as a set of servers that work together running the same service (for example, Active Directory Domain Controllers).

Difference Between Availability Set and Availability Zone

Depending on the SLAs required by different organizations, Azure includes different options for building and configuring high availability solutions. Availability Zones are unique physical locations within an Azure Region (set of datacenters). Each zone is made up of one or more data centers equipped with independent power, cooling and networking resources.

The main difference between Availability Zones and Availability Sets is that Availability Zones protect your resources from a potential datacenter failure, whereas Availability Sets only offer protection from hardware failures within a datacenter, thus increasing SLA coverage from 99.95% to 99.99%.

Set Up an Availability Set in Azure

To configure an Availability Set in Azure, two steps are required: the creation of the Availability Set and the assignment of VMs.

Create an Availability Set

To create an availability Set from the Azure portal, follow these steps:

  1. Log on to your Azure account.
  1. Click on Create a Resource, search for Availability Set, and click on the Create button.
  1. Fill the Subscription, Resource Group, Name and Region fields according to your requirements. Next, specify the number of fault domains and update domains needed for this Availability Set. Azure automatically manages the distribution of virtual machines among the created domains, always ensuring the best possible configuration within a group. For this example, we configure two fault domains and two update domains.

Figure 1 - Azure Availability Set

  1. Click on the Review + create button. Once the validation process is complete, click on the Create button.
  1. Once the deployment is complete, you can explore the resource and review its features before assigning new virtual machines.

Availability Sets can also be created using Azure PowerShell.

Assign a Virtual Machine

You assign a VM to an Availability Set through the Create a virtual machine wizard. Under the Basics tab, locate the Availability options field. Select Availability set from the drop-down list, and choose the Availability Set resource needed for the VM being created. Complete the rest of the configuration fields according to your requirements.

Figure 2 - Azure Availability Set

Important things to note are that VMs can be included in an Availability Set only when they are being deployed (existing machines cannot be assigned to an Availability Set), and that the Availability Set of a virtual machine can’t be changed after being created.

Read more regarding how Azure distributes virtual machines among existing fault and update domains.

Parallels RAS on Microsoft Azure

Parallels® Remote Application Server (RAS) supports both hybrid and cloud deployments on Microsoft Azure. Organizations can increase the flexibility and reliability of their Parallels RAS solution by combining Azure native resources, such as Azure Load Balancer, to load balance the front-end traffic and Availability Sets for the Parallels RAS Secure Client Gateways and Parallels RAS Publishing Agents.

Parallels RAS supports Microsoft Azure Hypervisor as a virtual desktop infrastructure (VDI) provider, thus enhancing flexibility and scalability to provision and scale VDI and Remote Desktop Session Host (RDSH) workloads on demand. In combination with Parallels RAS auto-scaling and auto-provisioning features, organizations can optimize their resource usage, which is very important for reducing unnecessary costs when working with cloud providers.

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References

Microsoft

TechNet

Azure Stack Blog