There is no need to shutdown the application because you should be able to carry out the operating system upgraded without an outage to the database particularly since you have a lot of nodes in your cluster.
Provided your cluster has sufficient capacity, you might even have the ability to upgrade multiple nodes in parallel to reduce the upgrade window. If you decide to do nodes in parallel and you fully understand the token allocations and where the nodes are positioned in the ring in each DC, make sure you only upgrade nodes which are at least 5 nodes "away" to the right so you know none of the nodes would have overlapping token ranges and they're not replicas of each other. Other points to consider are: - If a node goes down (for whatever reason), I suggest you upgrade the OS on the node before bringing back up. It's already down so you might as well take advantage of it since you have so many nodes to upgrade. - Resist the urge to run nodetool decommission or nodetool removenode if you encounter an issue while upgrading a node. This is a common knee-jerk reaction which can prove costly because the cluster will rebalance automatically, adding more time to your upgrade window. Either fix the problem on the server or replace node using the "replace_address" flag. - Test, test, and test again. Familiarity with the process is your friend when the unexpected happens. - Plan ahead and rehearse your recovery method (i.e. replace the node) should you run into unexpected issues. - Stick to the plan and be prepared to implement it -- don't deviate. Don't spend 4 hours or more investigating why a server won't start. - Be decisive. Activate your recovery/remediation plan immediately. I'm sure others will chime in with their recommendations. Let us know how you go as I'm sure others would be interested in hearing from your experience. Not a lot of shops have a deployment as large as yours so you are in an enviable position. Good luck! On Thu, Jan 30, 2020 at 3:45 PM Anshu Vajpayee <anshu.vajpa...@gmail.com> wrote: > Hi Team, > What is the best way to patch OS of 1000 nodes Multi DC Cassandra cluster > where we cannot suspend application traffic( we can redirect traffic to one > DC). > > Please suggest if anyone has any best practice around it. > > -- > *C*heers,* > *Anshu V* > > >
