Yes, that's essentially what it does do. It's a virtual client access point into the AlwaysOn group. Connecting via an appropriately configured listener with appropriately configured AlwaysOn group replicas could resulty in different connections being routed to different replicas within the AO group. For instance all read only connections might be routed to a secondary, away from the Primary replica and its database.

However, it's a cluster resource and is subject to the WSFC control.

Part 2 of my guide will be hitting the cluster and quorum configuration quite hard, keep an eye out for it. Have you read part 1 yet?

Since you aksed so nicely!!

When you first create the AO group you are informed of the option of creating a listener, selecting this will require the following

• unique Virtual IP address
• unique Virtual networkname
• a TCP port number

Once the listener has been created i urge you to go to the Failover Cluster Manager and look at the cluster applications\roles. You'll see a role with the same name as the AlwaysOn group that you created. Within the role will be 3 resources,

• Virtual Networkname resource
• Virtual IP address resource
• AlwaysOn listener resource

The role tracks the primary replica when failing over as a direct result of an AlwaysOn group level failover. To see an example, assume the following configuration

Windows Cluster 192.168.0.165

Nodes are

Nodename Node IP

ClusterNode1 192.168.0.166

ClusterNode2 192.168.0.167

ClusterNode3 192.168.0.168

ClusterNode4 192.168.0.169

The cluster nodes have the following instances installed. AOINST3\A3 is a failover cluster instance of SQL Server across nodes 3 and 4 only

Nodename Instancename Instance IP address

ClusterNode1 AOINST1\A1 192.168.0.171

ClusterNode2 AOINST2\A2 192.168.0.172

ClusterNode3 AOINST3\A3 192.168.0.173

ClusterNode4 AOINST3\A3 192.168.0.173

An AlwaysOn group "MyHA" has been created across the 3 instances. During the creation wizard a listener was configured with the following detail

Virtual Networkname Virtual IP Address

MyHAListener 192.168.0.175

Given this we will look at 3 scenarios

Primary failover from AOINST1\A1 to AOINST2\A2

Looking at the Listener clustered role ownership before failover will list ClusterNode1 as the role owner. Once the failover has been completed within the AO group, the new owner of the Listener clustered role will be ClusterNode2

Primary failover from AOINST3\A3 to AOINST\A1 (where AOINST3\A3 is active on ClusterNode3)

Looking at the Listener clustered role ownership before failover will list ClusterNode3 as the role owner. Once the failover has been completed within the AO group, the new owner of the Listener clustered role will be ClusterNode1

Primary failover from AOINST2\A2 to AOINST\A3 (where AOINST3\A3 is active on ClusterNode4)

Looking at the Listener clustered role ownership before failover will list ClusterNode2 as the role owner. Once the failover has been completed within the AO group, the new owner of the Listener clustered role will be ClusterNode4