Add a secondary node to an ApsaraDB RDS for MySQL cluster to distribute read traffic across more nodes. The operation does not interrupt existing read or write workloads. A cluster supports up to eight secondary nodes.
Prerequisites
Before you begin, make sure that:
The instance series is Cluster Edition
The instance status is Running
Billing
For more information about the billing rules after nodes are added, see Specification changes.
Add a node
Go to the Instances page. In the top navigation bar, select the region where the instance resides. Find the instance and click its ID.
On the Basic Information page, go to the Instance Topology Management section and click Add or Delete Node.
In the dialog box, select Add Node and click Next.
In the Node section, click the
icon or Add a Node, then configure the following settings:To remove the new node entry, click the
icon to the left of the node entry.Setting Description Zone The zone where the new node is deployed. Instance type The compute specification for the new node. vSwitch The vSwitch within the selected zone. 
Read the terms of service and click Confirm Order.
The node is added when the instance status changes from Adding Node to Running.
What to do next
After the node is added:
Configure the read weight of the cluster's read-only endpoint to distribute read traffic to the new node and balance the load across all nodes.
To add a node programmatically, call the CreateDBNodes API operation.