SQL Always On Active Active Cross premises

Question

Hi fellows,

Can an on-premises SQL AlwaysOn Cluster (2 Node) be extended to Azure (2 additional nodes as Azure VMs) in an active-active model?
On-premises SQL cluster has three availability groups.

Objective is to convert applications to active-active model. where as application layer can easily be configured for active-active scenario. However the databases need to be automatically available on DR, in case if the primary site SQL goes down (planned or unplanned) there should not be any manual intervention required.

Guidelines from anyone who has implemented this before would be very helpful.

Regards.

Answer 1

If by "active-active" you mean having running SQL Instances running secondary replicas of the database, then yes.

You'll need to carefully plan your cluster heartbeat settings, and your quorum model (see eg Cloud Quorum).

Because while it's technically possible to have automatic failover in this scenario, it's difficult. For most applications it's better to have a single async secondary in Azure and the primary and a synchronous secondary on-prem.

The difficulties are:

1) Only synchronous secondaries support automatic failover, and having a synchronous secondary in a remote datacenter can have a serious impact on performance.

And if you want automatic failover, you can't have a quorum voting majority in your datacenter; instead the quorum needs to be in the cloud, eg using Cloud Witness, which necessarily means:

2) In case of a temporary network issue between your Datacenter and Azure the nodes in your datacenter will go offline and the database will fail over.

And you'll need to carefully adjust the cluster timeout values which are always a tradeoff between failover time and false outages.

Answer 2

Hi @Junaid Ahmed ,

Can an on-premises SQL AlwaysOn Cluster (2 Node) be extended to Azure (2 additional nodes as Azure VMs) in an active-active model?

Yes.
Guidelines as this : Rehost an on-premises application with Azure VMs and SQL Server Always On availability groups

BR,
Mia

---

If the answer is helpful, please click "Accept Answer" and upvote it.

Answer 3

Hi @Junaid Ahmed ,

Is the reply helpful?

BR,
Mia

---

If the answer is helpful, please click "Accept Answer" and upvote it.