Clustering in MongoDB - MongoDB High Availability - page 36

Implementing clustering in MongoDB
In this section, we will go through the implementation of a cluster in MongoDB using
sharding and replica sets.
Note
A sharded cluster consists of three configuration processes, one or more replica sets, and
one or more mongos routing processes.
You can view this at http://docs.mongodb.org/manual/reference/glossary/#term-sharded-
cluster .
A sharded cluster in MongoDB consists of three components, configuration servers, shards
(replica sets or mongod processes), and mongos . The mongos process is the query router
for all clients.