DDS cluster instances consist of mongos, config, and shard nodes. The following diagram shows the node relationships.
Figure 1 Diagram of node relationships
mongos
A mongos is a router for reading and writing data, providing a unified interface for accessing DB instances.
- Each DB instance has 2 to 16 mongos. You can specify the quantity.
- A mongos reads configuration settings from configs and allocates read and write requests to shards. You can connect to a mongos directly.
config
A config stores configuration settings for DB instances and consists of one replica set.
- The availability of a config is the prerequisite to deploying a DB instance or modifying the instance information.
- You cannot connect to a config directly.
shard
In the cluster instance, shards are used to store user data.
- Each DB instance has 2 to 16 shards. You can specify the quantity.
- Each shard is deployed as a replica set to ensure data redundancy and high reliability.
- You cannot connect to a shard directly.