Whats the difference CNAME vs Listener in AlwaysON AG?

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Whats the difference CNAME vs Listener in AlwaysON AG?

vsamantha35

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Points: 11551
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June 3, 2017 at 2:07 am

#337451

Hi Experts,
In our environment we have Alwayson 2014 Availability Group setup and has a listener. But I also see a Active directory CNAME record was created and that is been using for application connection string or even while connecting through Management studio. What to know like what is the advantage of having/using CNAME record instead of using Alwayson Listener name in the connection strings.
I want to know this because recently we arent able to connect to AG server using CNAME. Wasnt able to ping the server , unable to TS/remote login to the sever using CNAME. But using invidual servernames/replicas I am able to ping and also able to make remote connection using mstsc, also able to connect vis SQL Server Management studio.
First of all why do someone even create CNAME record for SQL Server?
Thanks,
Sam

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Lowell SSC Guru Points: 323518 More actions · Answer 1

we create CNAMES and make our Developers use those for connection strings specifically so we can upgrade or replace servers behind the scenes.
if everyone connects to the cname [SuperServer], and under the hood the cname points to SQLPRD01FL, i can build a new server to replace SQLPRD01FL, and when the server is ready, i can simply move the cname to point to another server, IE [NewClusterPRD01] or something. no need to change every connection string that had SQLPRD01FL; that means modifying packages, environmental variables, and custom applications/web servers with config files don't need to be touched just because a server is replaced, or got struck by lighting or viruses, etc.

it makes administration cleaner;
replication hates cnames though,and those haveto point to actual machine names.

Lowell

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vsamantha35 SSChampion Points: 11551 More actions · Answer 2

But Sir, the Always on AG Listener is also meant for the same purpose then why CNAME record to be created separately. Correct If I am wrong.

Lowell SSC Guru Points: 323518 More actions · Answer 3

Right, but the administration of everything else except availability groups or replication can be simplified. So yes, the cname is not helpful for that, but it will save time on other things.

Lowell

--help us help you! If you post a question, make sure you include a CREATE TABLE... statement and INSERT INTO... statement into that table to give the volunteers here representative data. with your description of the problem, we can provide a tested, verifiable solution to your question! asking the question the right way gets you a tested answer the fastest way possible!