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What happens with a Hyper-V 2012 Cluster with only one DC, if the DC suddenly goes down?

Would the Hyper-V Cluster works after a reboot, if the DC is missing?

Or should we have two DCs?

Jacob Bach Pedersen
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If your only domain controller goes down, you will not be able to authenticate to the domain or access configuration data stored therein. Things such as the cluster service account will be unable to log on. Your domain controller is probably hosting DNS too, which you're also going to need to stay up if you want a happy cluster. The list goes on.

You always want at least two domain controllers in your domain if at all possible. And at least one of those DCs needs to be outside of your cluster.

Ryan Ries
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    Thanks. Is it okay to host one of the DCs on the cluster as a VM? Or should it be running at the host it selfs. – Jacob Bach Pedersen Nov 27 '13 at 21:08
  • No do not put Active Directory in the parent partition of a Hyper-V host. No other roles should be installed on a Hyper-V host. But yes it is OK to have one of your DCs as a VM in the cluster. I just recommend a physical one that is outside cluster in case one or both of the cluster nodes blows up for some reason. Even an inexpensive, 1U entry level HP would be fine. – Ryan Ries Nov 27 '13 at 21:12
  • I'm not saying that you cannot technically install AD and Hyper-V on the same machine, I'm just saying that it's not recommended. The idea is to keep your infrastructure as modular as possible, so that if you suffer a hardware failure one machine, you don't lose everything. – Ryan Ries Nov 27 '13 at 21:17
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AFAIK, cluster bootstrapping in Windows Server 2012 allows an existing cluster to not only boot but to operate without a Domain Controller being available. An available DC is required to create a cluster but once it is created the cluster can boot, operate and be joined without a DC being available. Microsoft also removed the AD dependency from Cluster Shared Volumes so that your CSV can be mounted and accessed without an available DC.

In Windows Server 2012 Microsoft has removed or remediated many of the "chicken or the egg" dependencies related to the Cluster and CSV dependency on AD.

I can't speak to Windows Server prior to 2012 but in Windows Server 2012 the Cluster service runs as Local System.

joeqwerty
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  • Upvoting you because I was thinking about speaking to this exact topic, but, well you want a DC up anyway, right? :) – Ryan Ries Nov 28 '13 at 04:07
  • I agree but I did want to point out the improvements made in Windows Server 2012 related to AD dependencies and failover clusters. – joeqwerty Nov 28 '13 at 04:08
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Would the Hyper-V Cluster works after a reboot, if the DC is missing?

How can it, given that the Cluster configuration data is stored on the DC. YOu would not be the first to run into a boot problem (though most people were "smarter" and put the DC's onto VM's in the cluster - same result on a reboot).

ALWAYS have at least 2 DC's.

TomTom
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I completely agree with the above, always have at least 2 DCs. That being said, Microsoft introduced some new capabilities in Windows 2012 Failover Clustering to make it less reliable on DCs during startup of the cluster services. This will enable a failover cluster to boot to an operational state without having access to a DC.

This is described here:

http://blogs.technet.com/b/wincat/archive/2012/08/29/windows-server-2012-failover-cluster-enhanced-integration-with-active-directory-ad.aspx (Search for "AD-less Cluster Bootstrapping")

Trondh
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  • It almost sounds like the new 2012 cluster, is build to run all DCs on VMs. But all other posts here, do not sounds like that. – Jacob Bach Pedersen Nov 28 '13 at 20:38
  • All I'm saying is what Microsoft is saying :-) Personally I would always go with minimum 2 DCs per site. The cost is minimal compared to the resiliency you achieve. Just be sure to run the DC VMs on separate nodes in your cluster. – Trondh Nov 28 '13 at 20:43