Availability Cloud Witness during Azure region failure

Adam Erot 51 Reputation points
2020-06-15T17:07:25.9+00:00

Hello there,

I have a question about Cloud Witness.

In many articles about Failover Cluster at Azure, we can find infomation about usage of Cloud Witness as quorum witness.

Assume that we want to create SQL Server Always on Availability Groups in multiple Azure regions (ref.: https://learn.microsoft.com/en-us/azure/architecture/reference-architectures/n-tier/multi-region-sql-server )

Then we will create cloud witness in primary region (because in some region we have to create it).

The question - what happens when the primary region will be down/offline ? Where I assume the Cloud Witness will be down too. Nevertheless, the failover should work correctly?

Thank you in advance for your responses.

Best Regards,
AErot

Azure Cloud Services
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  1. vipullag-MSFT 25,866 Reputation points
    2020-08-07T06:35:35.057+00:00

    @Adam Erot

    Apologies in delayed response. I checked with internal team on this to get more details.

    Whether the cluster continues running depends on how many nodes are online in the other regions—the remaining nodes need a majority of votes in the cluster quorum, which could be tricky if you have two nodes + the cloud witness go down together.

    Here is an example of four nodes plus a witness:
    • In this example, if you had two nodes + the witness go offline, the cluster would go down because the remaining two nodes have 2/5 of the votes, which doesn’t comprise a majority.
    • I’m thinking in this kind of scenario, you might want to put the cloud witness in a different region than the primary region so it can act in its intended role as an external tiebreaker.

    Hope this info helps.

    Please 'Accept as answer' if the provided information is helpful, so that it can help others in the community looking for help on similar topics.

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