SQL - Always on avilabilty - Patch updates

Question

we have servers SQL always-On config like below,

Node1 -- primary
Node2 -- seconday1 (automatic ,synch)
Node3 -- secoday2 (manual, synch)

we plan to update patch on both seconday1& 2 on weekdays ( like Wednesday), then Sunday on primary.

so the secondary node updated on Wednesday. till Sunday the Primary is not upto date.

is this create any noise? what are the cons on this ?

we have 1day downtime on sunday only , so that we plan all primary on sunday.

Answer 1

Hi @KIRUBAKARAN J A ,

what are the cons on this?

In addition, during the upgrade process, a secondary replica will not be available for failover or for read-only operations, and after the upgrade, it may take some time for the secondary replica to catch up with the primary replica node depending upon the volume of activity on the primary replica node.
For recommendation about upgrading Always On, please refer to this official documentation.
And as Shashank said, it is better to apply patches on AG’s all nodes on Sunday.
Best Regards,
Amelia

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Answer 2

is this create any noise? what are the cons on this ?

No it should not, as a matter of fact lot of AG users do this. And since you are updating primary on Sunday you should be good. Just make sure if failover happens between this period you "may" see some issues. So get approval from management on this. I answered similar question on how-long-can-cu-and-sp-be-different-across-a-sql-server-always-on-cluster-nodes

we have 1day downtime on sunday only , so that we plan all primary on sunday.

1 day downtime is enough to patch whole AG why are you then planning to keep nodes on different CU level ? I would suggest apply patches on all nodes on Sunday. You will be happy and so will be your customer.

cons

Please note that applying SP on secondary replica would need a reboot, most likely and you need to make sure that AG dashboard is in Sync before doing reboot. You need to be careful. If you want to avoid this risk do it on Sunday when you have a day downtime.