Hidden replica set do not take part in election

Question

I have a replica set of three server and a backup server, The backup server is made

"hidden"=true and "priority"=0`

My concern is when I have one of my secondary and backup server up, my secondary does not changes into primary, which means hidden server is not taking part in election, but as per the mongo document, it cannot become primary but takes part in election. Is their some extra configuration required to do so?

Answer 1

Replica set member cannot become primary if is unable to connect to a majority of replica set members. If you have four members in a replica set you need to be be able to communicate with three and if only two members are up it is clearly impossible. If you really want configuration like this you should add arbiter to the replica set.

Generally speaking you should avoid even number of members in the replica set.