Hybrid Clusterless and Clustered AGs

  • I'm trying to find out if it's possible to build a hybrid AoHA environment, where two nodes in the AG are Clustered, but there is a 3rd node that is not part of the cluster. The idea is to create a read only replica for a client's hosted databases that's independent of our domain.

    Logic tells me this should be possible, but I can't find anything indicating it is or isn't.

    While Replication or CDC could produce a similar configuration, the environment uses Contained databases, and these two options don't work with contained Databases.

     

    Leo
    Nothing in life is ever so complicated that with a little work it can't be made more complicated.

  • I would suggest looking into Distributed Availability Groups. A Distributed Availability Group is an 'AG of AGs'; it is comprised of two or more AGs. The Primary Replica on the Primary AG of a Distributed Availability Group replicates to all of the Secondary replicas in its own AG, and to the Primary Replica of the Secondary AGs. The Primary Replica on the Secondary AG(s) replicate to their Secondary Replica(s), if any.

    MSFT Doc: 'What is a distributed availability group' https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/distributed-availability-groups?view=sql-server-2017

    You can create an AG with only 1 replica - (the new read-only client database replica), and join that AG and your existing AG into a single DAG.

    I've never tried joining a non-clustered AG to a Distributed AG, but we have plenty of Distributed AGs built from single-replica AGs hosted on separate clusters.

    -Eddie

    Eddie Wuerch
    MCM: SQL

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