Configuring Distributed Availability Group with multiple SQL instances

Question

I am trying to create multiple SQL instances each with its own AG (and listener) on 2 Windows clusters in a Distributed AG as follows:

• Two sites - Primary & DR

• Each site has a WSFC configuration - PrimCluster & DRCluster.

• PrimCluster has two nodes - PrimNodeA & PrimNodeB

• DRCluster has two nodes - DRNodeA & DRNodeB

• Each node has two SQL AG replicas each with an AG (with its own listener) as follows:

• on PrimNodeA & B - Instance1_P_AG

• on PrimNodeA & B - Instance2_P_AG

• on DRNodeA & B - Instance1_DR_AG

• on DRNodeA & B - Instance2_DR_AG

• DAG configuration asynchronous between the two clusters.

• Each local AG is synchronous availability mode and holds its own AG databases.

• all the secondaries are non-readable

This is my first experience with multiple SQL instances on a cluster, each configured with AG and DAG between the two clusters.

My Question please:

• In order to create the DAG, do I need to create a DAG per AG pair as follows:
• Instance1_P_AG and Instance1_DR_AG
• Instance2_P_AG and Instance2_DR_AG

In other words, do I need multiple DAGs or just one between Instance1_P_AG and Instance1_DR_AG will cover all instances in each cluster?

Also, I would appreciate a link to an article on multiple SQL instances in a DAG.

Thank you

Answer 1

In other words, do I need multiple DAGs or just one between Instance1_P_AG and Instance1_DR_AG will cover all instances in each cluster?

A Distributed Availability Group is an Availability Group across two Availability Groups. You'll need a Distributed Availability Group for each Availability Group you'd like to extend.

SQL Server Instances on the same server do not talk to each other in any capacity, each instance is treated as though there were no other instances on the server.