ApsaraDB for MongoDB supports cluster versions. The cluster version and the three-node replica share the same system architecture, using the HA control system, log collection system, monitoring system, online migration system, backup system, and task control system described in the preceding image.
The cluster version provides three components: mongos (service agents), shards (shard servers), and the ConfigServer. You can freely select the number and configuration of mongos and shard nodes and set up MongoDB clusters with different capabilities. The product architecture is as follows:
One mongo is configured with one single node. You can purchase multiple mongos to achieve load balancing and failover capabilities. A single cluster version instance can support 2-32 mongos nodes. For more information, see Correct method for connecting to MongoDB clusters.
Shard nodes are shard servers. Currently, they are structured as three-node replica sets. You can upgrade and downgrade their configurations, but cannot change the number of nodes in the replica set. A single cluster version instance can support 2-32 shard nodes.
The ConfigServer is the essential component of the cluster and its default configuration is a 1-core 2 GB CPU and 20 GB storage space. Now, you cannot upgrade or downgrade this configuration.
The cluster allows you to add mongos and shard nodes, but you cannot do this using native commands. Instead, you must purchase new mongos and shard nodes through the console.
None of shards and the ConfigServer provide domain name access, but you cannot connect to them directly to perform operations. All data operations require you to connect to mongos which then issue the commands.
To use the cluster mode, you must purchase a new instance. Now, you cannot upgrade existing three-node replica sets to cluster versions.