• Talk to a MongoDB Expert About Scaling 6 

• MongoDB Deployment Topology Consulting Package 7 

• Quick Reference Cards 8 

## 10.2 Sharding Concepts 

These documents present the details of sharding in MongoDB. These include the components, the architectures, and the behaviors of MongoDB sharded clusters. For an overview of sharding and sharded clusters, see Sharding Introduction (page 661). 

Sharded Cluster Components (page 668) A sharded cluster consists of shards, config servers, and mongos in- stances. 

Shards (page 669) A shard is a mongod instance that holds a part of the sharded collection’s data. 

Config Servers (page 670) Config servers hold the metadata about the cluster, such as the shard location of the data. 

Sharded Cluster Architectures (page 671) Outlines the requirements for sharded clusters, and provides examples of several possible architectures for sharded clusters. 

Sharded Cluster Requirements (page 671) Discusses the requirements for sharded clusters in MongoDB. 

Production Cluster Architecture (page 672) Outlines the components required to deploy a redundant and highly available sharded cluster. 

Continue reading from Sharded Cluster Architectures (page 671) for additional descriptions of sharded cluster deployments. 

Sharded Cluster Behavior (page 674) Discusses the operations of sharded clusters with regards to the automatic bal- ancing of data in a cluster and other related availability and security considerations. 

Shard Keys (page 674) MongoDB uses the shard key to divide a collection’s data across the cluster’s shards. 

Sharded Cluster High Availability (page 676) Sharded clusters provide ways to address some availability con- cerns. 

Sharded Cluster Query Routing (page 678) The cluster’s routers, or mongos instances, send reads and writes to the relevant shard or shards. 

Sharding Mechanics (page 684) Discusses the internal operation and behavior of sharded clusters, including chunk migration, balancing, and the cluster metadata. 

Sharded Collection Balancing (page 684) Balancing distributes a sharded collection’s data cluster to all of the shards. 

Sharded Cluster Metadata (page 689) The cluster maintains internal metadata that reflects the location of data within the cluster. 

Continue reading from Sharding Mechanics (page 684) for more documentation of the behavior and operation of sharded clusters. 

