How to isolate 1 MongoDB config server

Question

I need to preform a rolling upgrade on my MongoDB. I've been all over the Mongo documentation and I can't find a solution to my problem (if there is one) Here's a simple sketch of the Architecture:

I have two Sites (A and B) (telecommunications site, not website). When I'm executing a rolling upgrade in one site I need to upgrade everything associated to it.

I place my site B in contingency (there are no requests from outside arriving to that Site) and I start upgrading everything, but when I get to the config server I find a problem.

Config servers are always in sync, and this can't happen because all communication with the outside must be terminated.

Is there a way to isolate the config server on that site? (I know they're replicated) I hope you guys understand my question, is basically how to preform a config server rolling upgrade in multi-host environment without completely stopping all 3 config servers (stopping both sites is not a valid solution)

Will upgrading my config server will have any impact in my service? (in the other site)

Can I shut down 1 config server, upgrade and restart it?

thanks

Answer 1

Yes, you can simply stop one config server, upgrade and restart it. That is one of the reasons why there are three: even when taking down one, there are two others to read from, so one might fail.

A few things to keep in mind, though:

• When one config server is down, the cluster meta data is read only: no chunk splits or migrations during that time. So in order to prevent JumboChunks, you better hurry a bit.
• Talking of JumboChunks: you should check your cluster for them after update
• As for the order: Start with the last server in your configdb string, finish with the first
• Always, Always, ALWAYS read the migration guide of the version you are updating to