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Hyper‑V high availability.

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Let's start by defining our terms.

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What exactly is meant by high availability?

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High availability for our context,

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and you can see the my citation in the lower part of the slide,

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involves the implementation of controls that guarantee your workload is up

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and running despite maintenance operations and outages.

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All right?

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Now, the words on this definition I think are very intentional.

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We have guarantee.

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You may very well be subject to service‑level agreements,

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SLAs, with your employees, with your colleagues,

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with your customers, whomever,

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where you actually quantify the degree of availability your workload has.

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And if your service is down over that SLA amount due

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to a planned or unplanned event,

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this could have big repercussions for your business,

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and frankly, for your job security.

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So we need to understand in Hyper‑V, and speaking as

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Hyper‑V hybrid cloud administrators,

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what are the main Microsoft‑provided options for doing high

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availability workloads in Hyper‑V virtual machines?

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Well, there's two kinds of clustering we'll learn a bit about.

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There's host clustering and guest clustering, and we also have the

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Windows Server Network Load Balancing service,

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also called NLB. Now I'm not going to get deep into the weeds

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in Windows Server failover clustering here because exam AZ‑801

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goes much deeper into clustering.

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So at this point, I just want to be able to differentiate, or I

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want you to be able to differentiate, the two types of

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clustering that we're talking about here.

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Now,

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first of all, to take a step back, clustering is generally speaking

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where you have shared storage between N number of nodes

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participating in the cluster. Now I say generally speaking because

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there are technologies where you can do Windows Server failover

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clustering without shared storage.

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We'll get into that in the AZ‑801 skill set, but let's just kick

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it old school and assume that we've got network accessible or

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locally attached shared storage and we have N number of nodes

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participating in the cluster.

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Now,

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the way that Windows Server failover clustering works is that

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one node is going to be the active node for that clustered

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role, and one of the most common,

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if not the most common clustered role, is the Hyper‑V virtual machine.

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So in this case, the right‑most node,

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the one that's in the three o'clock position, is active for that

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VM, and connectivity happens to that VM by coming into the

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failover cluster's virtual IP address.

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Now,

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what makes failover clustering a high availability solution is

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that if we need to take that node offline,

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the one that's hosting the VM, we can manually move that VM to another node in

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the cluster with minimal or preferably no service disruption.

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Likewise,

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if that node were to go down unexpectedly, the other nodes in the cluster

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are aware via heartbeat messages who's up and who's down, and in that case,

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another node will grab control over that VM.

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How is the node able to grasp that control?

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Well,

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because the VM and its definitions are in that shared storage that's

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accessible to all of the nodes in the cluster. You see the magic there? The

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reason why we're calling this Hyper‑V host clustering is because, in this

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case, your three nodes that are in this diagram are Hyper‑V hosts, as well

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as members of a failover cluster, and the virtual machine is what's called

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a clustered role.

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Now, there is a more specialized version of Windows Server failover clustering.

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What if you have a virtualized infrastructure where you have your

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Hyper‑V hosts, in this case, NodeA1, A2, and A3, and they are, of

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course, hosting virtual machines and highly available file shares and

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SQL Server databases, etc., and offering those clustered roles under

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virtual IPs as usual.

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But what if you wanted to create an internal failover cluster within your

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virtual machine infrastructure? A‑ha! In other words,

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from within the guest VMs. Is it possible to set up a failover

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cluster and advertise services under a virtual IP?

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And, of course, the answer to that is yes. This is

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called Hyper‑V guest clustering.

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Now, there are quite a few implications in terms of how you'd want this to work.

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Of course, one big one would be your cluster nodes really

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should be on top‑level cluster nodes.

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In other words,

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notice that I've gotten NodeB1 virtual machine that's

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being managed by the active node,

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NodeA1, but NodeB2, another member of that guest cluster, is on NodeA2.

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So what you have here is two levels of high availability to where you're

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protecting the VMs that are forming the guest cluster, and then within

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the guest cluster VM's operating system,

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there's another failover cluster where you've got high

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availability for services there. Yes, it's kind of complex and meta, but there you go.