Fault Domains vs Update Domains

Azure Resource Manager Virtual Machines

Virtual Machines are a very foundational and fundamental resource in Cloud Computing. Deploying virtual machines gives you more flexibility and control over your cloud infrastructure and services, however, it also means you have more responsibility to maintain and configure these resources. This course gives you an overview of why use virtual machines as well as how to create, configure, and monitor VMs in Azure Resource Manager.

Azure Resource Manager Virtual Machines: What You'll Learn

Lesson	What you'll learn
Overview	Overview of the course and the Learning Objectives
What is a Virtual Machine?	Understand what are Azure Virtual Machines and what workloads are ideal for VMs
Creating and Connecting to Azure VMs	Learn to deploy Windows and Linux VMs as well as how to connect to these VMs
Scaling Azure Virtual Machines	Understand VM scaling, load-balancing, and Availability Sets in Azure Resource Manager
Configuration Management	Understand the basic concepts of Desired State Configuration and the options available to Azure VMs
Design and Implement VM Storage	Gain an understanding of the underlying Storage options available to VMs as well as Encryption
Configure Monitoring & Alerts for Azure VMs	Learn to monitor VMs in Azure Resource Manager as well as configure alerts.
Summary	Course summary and conclusion

 

In learning how to scale our Azure virtual machines we must first understand what Microsoft calls Fault Domains and Update Domains.

If you were to imagine an image of a Datacenter which has what we call a “rack” of servers, or a group of servers all connected to the same power and networking equipment, then this would be what is referred to in Azure as a Fault Domain (FD). So I have a server on a rack, so what? Well, imagine you are managing a web service which you provided across two different web servers that happen to be on two different racks and thus two Fault Domains. Because each rack shares the same power and network sources separate from other racks, if one of your web servers in one Fault Domain were to go down due to a power or network failure, you still have the other rack available that houses your second web server and your web service continues to operate. To guarantee that this happens you’d have to put your two web servers in what’s called an Availability Set which we will learn about shortly. Azure has an 99.95% SLA for availability of your VMs as long as they are in an Availability Set.

Now let’s contrast this with Update Domains (UD). Just like on-premises there is sometimes a need to bring a server down for reasons such as needing to patch the server or install updates on the underlying host in which case you need to purposely bring down all your servers, however, you’d need to bring them down in a staggered approach. Using Update Domains allows you to accomplish this. You should know that Microsoft does all this for you if you’re using Azure as Platform as a Service or Software as a Service, however remember that in our case we’re using Azure as Infrastructure as a Service, and thus we not only have full control of our VMs, but it is also our responsibility to configure how VMs are updated ourselves.