Primary & DR site with 5 node mongodb. Do i need Arbiter

[Nikhil R]

We are planning a 5 node env i.e 3 nodes in Primary DC & 2 in DR DC.

If my primary DC goes down, i assume one of the node in the DR DC gets elected as a Primary until Primary DC comes up.

Is my assumption true.

Or do we need an arbiter to elect a Primary in DR DC as we will have 2 nodes available?

[Rhys Campbell]

No, the nodes in the DR DC would only be able to summon up 2 votes. You need a majority, *3/5 in your case, to elect a PRIMARY. So if you main data centre goes down your replicaset is read-only.

Here's a good link that contains some recommended topologies...

https://docs.mongodb.com/manual/core/replica-set-architecture-geographically-distributed/