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I joined a new company this week where I noticed that one always on setup has listener ip configured, while the other doesn't. For the AG setup which doesn't have the listener in it, will the applications connect to the cluster ip address? Can i add the listener at this point of time? What are the HA options if Listener is not present?

First two screenshots show one AG setup without the listener

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For the AG setup with the listner and the fileshare witness

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Not having a listener IP means that you will get the functionality provided by a FCI (Failover Cluster Instance) rather than a fully fledged AG + FCI solution. In effect you are asking what are the effects of using a FCI as a data source as opposed to an AG and how can I expand on it.

The FCI will require you to stop a service on one node with shared storage and wait for it to start on a different node after the resources are started on it. This takes time. By using this IP you will have to deal with this downtime every time you patch or fail over.

An AG has the service running at all times on all the nodes and you get to set much better priority, along with assigning read only node options to your clients connection strings. This means faster failover, dynamic rerouting of applications with the READ_INTENT connection setting, and better management of your entire AG solution and cluster as a whole.

It is very simple to add or remove a listener so do not worry if you don't have one yet.

Edit to question: Having a listener or not in SQL Server doesn't affect a FCI failover unless you do something with the dependencies with each other. Outside of that a FCI will remain independent and operate on the instance level. The FCI will failover if there is a issue with the heartbeat or it's initiated, the AG solution with a listener will do so at the database level. Thus you can have your application working off an AG listener which can work independently of the FCI depending on how the solution is designed. We have some FCI/AG MCM's and experts here who can give you more in depth answers too.

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  • We actually had a production issue 2 days back when the log drive on the primary was filled and a fail over did not happen. I was thinking if adding a listener port would increase the HA options on this setup. Also, if there is no Listener doesnt the system perform an automatic failover because FCI is already present? Thanks for the followup!
    – buddinggeek
    Commented Dec 12, 2016 at 18:58
  • heya updated the question.
    – Ali Razeghi - AWS
    Commented Dec 12, 2016 at 19:02
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    Just to clear this up (for me), while AGs fail over databases in logical units of AGs - in 2014 there are no database level checks. A database could be offline and the AG will not fail. If you're using an FCI with an AG the unit of automatic failover will be the instance as the FCI takes precedence and AGs won't be able to auto failover. @user2923332
    – Sean Gallardy
    Commented Dec 13, 2016 at 3:47
  • Thanks @SeanGallardy, I was hoping you'd step in when I wrote my last line "We have some FCI/AG MCM's and experts here". The community is lucky to have everyone's expertise here like yours. Good insight, I didn't think of that.
    – Ali Razeghi - AWS
    Commented Dec 13, 2016 at 17:51
  • Thank you for the responses. While I understand this would work where there is shared SAN and FCI with no listener, the setup which I mentioned has no shared SAN and disks are independent. Would this configuration still make sense? Kindly clarify.
    – buddinggeek
    Commented Dec 20, 2016 at 5:00

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