Overview of Scaling In and Out an Instance

Adding CNs for an Instance

Instances can be scaled out by adding CNs. For example, if the original instance is configured with 1 CN, 3 replicas, and 1 shard, the instance will have 3 CNs, 3 replicas, and 1 shard after 2 CNs is added. For details, see Adding Coordinator Nodes for an Instance (Distributed).

Figure 1 Adding CNs for an instance

Adding Shards for an Instance

Instances can be scaled out by adding shards. For example, if the original instance is configured with 3 CNs, 3 replicas, and 1 shard, the instance will have 3 CNs, 3 replicas, and 3 shards after 2 shards is added. For details, see Adding Shards for an Instance (Distributed).

Figure 2 Adding shards for an instance

Deleting CNs for an Instance

Instances can be scaled in by deleting CNs. For example, if the original instance is configured with 3 CNs, 3 replicas, and 3 shards, the instance will have 2 CNs, 3 replicas, and 3 shards after 1 CN is deleted. For details, see Deleting Coordinator Nodes for an Instance (Distributed).

Figure 3 Deleting CNs for an instance

Main processes are running on the main CN (that is, the CN whose component ID is cn_5001), so this CN cannot be deleted for scale-in. You can call the Querying the Components of a DB Instance API to query cn_5001. To scale in the instance, another CN will be deleted. As shown in Figure 4, the CN whose component ID is cn_5003 is deleted instead.

Figure 4 Deleting CNs for an instance

Deleting Shards for an Instance

Instances can be scaled in by deleting shards. For example, if the original instance is configured with 2 CNs, 3 replicas, and 3 shards, the instance will have 2 CNs, 3 replicas, and 2 shards after 1 shard is deleted. For details, see Deleting Shards for an Instance (Distributed).

Figure 5 Deleting shards for an instance