Foursquare describes the 3 different replica set setups for their MongoDB servers:
- Straight-up replica set with arbiter node
- Replica set with dedicated read slaves and single backup node
- Shard on top of replica set with dedicated read slaves
If this all looks simple, it’s because it is. We’ve been very pleased with how replica sets have smoothed out the bumps in handling operational emergencies as well as for general maintenance and scaling out. Our next step is to configure our replica sets for data center awareness, which is not fully supported but workable with the latest version of MongoDB.
Original title and link: Foursquare Setup for MongoDB Replica Sets (NoSQL databases © myNoSQL)