Editor’s note: In partnership with Microsoft Press, now celebrating their 30th year, MVPs have been contributing to an ongoing guest series on their official team blog. Today’s article is from Cluster MVP David Bermingham which is the 44th in the series.
SQL Server High Availability in Windows Azure Iaas
When deploying SQL Server in Windows Azure you must consider how to minimize both planned and unplanned downtime. Because you have given up control of the physical infrastructure, you cannot always determine when maintenance periods will occur. Also, just because you have given control of your infrastructure to Microsoft it does not guarantee that you are not susceptible to some of the same types of outages that you might expect in your own data center. To minimize the impact of both planned and unplanned downtime Microsoft provides what are called Fault Domains and Upgrade Domains. By leveraging Upgrade Domains and Fault Domains and deploying either SQL Server AlwaysOn Availability Groups (AOAG) or AlwaysOn Failover Cluster Instances (AOFCI) you can help minimize both planned and unplanned downtime in your SQL Server Windows Azure deployment. Throughout this document when I refer to a SQL Server Cluster, I am referring to both AOAG and AOFCI. When needed, I will refer to AOAG and AOFCI specifically.
Fault Domains are essentially “a rack of servers”, with no common single point of failure between different Fault Domains, including different power supplies and network switches. An Update Domain ensures that when Microsoft is doing planned maintenance, only one Update Domain is worked on at a given time. This eliminates the possibility that Microsoft would accidentally reboot all of your servers at the same time, assuming that each server is in a different Update Domain.
When you provision your Azure VM instances in the same Availability Set, you are ensuring that each VM instance is in a different Update Domain and Fault Domain…to an extent. You probably want to read Manage The Availability of Virtual Machines to completely understand how VMs get provisioned in different Fault Domains and Update Domains. The important part of the availability equation is ensuring that each VM participating in your SQL Server cluster is isolated from each other, ensuring that the failure of a single Fault Domain or maintenance in an Update Domain does not impact all of your Azure instances at the same time.
So that is all you need to know….right? Well, not exactly. Azure IaaS does not behave exactly like your traditional infrastructure when it comes to clustering. In fact, before July of 2013, you could not even create a workable cluster in Azure IaaS. It wasn’t until then that they released hotfix KB2854082 that made it possible. Even with that hotfix there are still a few considerations and limitations when it comes to highly available SQL Server in Windows Azure.
Before we dive into the considerations and limitations, you need to understand a few basic Azure terms. These are not ALL the possible terms you need to know to be an Azure administrator, but these are the terms we will be discussing that are specific to configuring highly available SQL Server is Azure IaaS.
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About the author
David Bermingham is recognized within the technology community as a high availability expert and has been honored by his peers by being elected to be a Microsoft MVP in Clustering since 2010. David’s work as director of Technical Evangelist at SIOS has him focused on evangelizing Microsoft high availability and disaster recovery solutions as well as providing hands on support, training and professional services for cluster implementations. David hold numerous technical certifications and draws from over twenty years of experience IT, including work in the finance, healthcare and education fields, to help organizations design solutions to meet their high availability and disaster recovery needs. David has recently begun speaking on deploying highly available SQL Servers in the Azure Cloud and deploying Azure Hybrid Cloud for disaster recovery.
About MVP Mondays
The MVP Monday Series is created by Melissa Travers. In this series we work to provide readers with a guest post from an MVP every Monday. Melissa is a Community Program Manager, formerly known as MVP Lead, for Messaging and Collaboration (Exchange, Lync, Office 365 and SharePoint) and Microsoft Dynamics in the US. She began her career at Microsoft as an Exchange Support Engineer and has been working with the technical community in some capacity for almost a decade. In her spare time she enjoys going to the gym, shopping for handbags, watching period and fantasy dramas, and spending time with her children and miniature Dachshund. Melissa lives in North Carolina and works out of the Microsoft Charlotte office.