We would like to upgrade just a single slave in a 2.0.6 replica set to 2.2.3. This is in a sharded configuration. The reason for this is we want to just upgrade the most minimalistic portion of the set we can, so users can test with their code/drivers against the slave and ensure there aren't core incompatibilities.

We would then shut down everything and upgrade all components to 2.2.3 when they are sure everything works OK.

This doc: http://docs.mongodb.org/manual/release-notes/2.2/ Doesn't appears to address this situation directly. Can you commend on any potential issues with having 1 member of a RS in a sharded configuration as 2.2.3? We would reconfigure it so with priority = 0 so it can't become master.

I am testing this now, and so far it seems to be benign. But I want your official opinion. I have no problem updating the docs and doing a pull request should this be OK.