Creating a Read Replica

Scenarios

Read replicas enhance the read capabilities and reduce the load on your DB instances.

Procedure

1. Log in to the management console.
2. Click in the upper left corner and select a region.
3. Click in the upper left corner of the page and choose Databases > Relational Database Service.
4. On the Instances page, locate the target DB instance and choose More > Create Read Replica in the Operation column.
5. On the displayed page, configure information about the DB instance and click Next.
   Figure 1 Basic information
   

   Table 1 Basic information

   Parameter	Description
   Billing Mode	Yearly/monthly billing and pay-per-use billing are supported.
   Region	By default, read replicas are in the same region as your DB instance.
   DB Engine	Same as the DB engine of your DB instance by default and cannot be changed.
   DB Engine Version	Same as the DB engine version of the primary DB instance by default and cannot be changed.
   Storage Type	Determines the DB instance read/write speed. The higher the maximum throughput is, the higher the DB instance read/write speed can be. Cloud SSD: cloud disks used to decouple storage from compute. Extreme SSD: uses the 25GE network and RDMA technology to provide you with up to 1 million random read/write performance per disk and low latency per channel. NOTE: If you select DSS for Resource Type, only the storage type that you have selected when buying the DSS service is displayed by default.
   AZ	RDS allows you to deploy your DB instance and read replicas in a single AZ or across AZs to improve reliability.

   Figure 2 Specifications
   

   Table 2 Instance specifications

   Parameter	Description
   Instance Class	Refers to the vCPU and memory of a DB instance. Different instance classes have different numbers of database connections and maximum IOPS. After a DB instance is created, you can change its CPU and memory. For details, see section Changing a DB Instance Class. DB instances in a DCC only support the general-enhanced instance class.
   Storage Space	Contains the system overhead required for inodes, reserved blocks, and database operation. By default, storage space of a read replica is the same as that of the primary DB instance.
   Disk Encryption	Disable: indicates the encryption function is disabled. Enable: indicates the encryption function is enabled. Enabling disk encryption improves security but affects system performance. Key Name: indicates the tenant key. You can select an existing key or create a new one. NOTE: If you enable disk encryption during instance creation, the disk encryption status and the key cannot be changed later. After an RDS DB instance is created, do not disable or delete a key that is currently in use. Otherwise, RDS will be unavailable and data cannot be restored. For details about how to create a key, see "Creating a CMK" in Data Encryption Workshop User Guide.

   Figure 3 Connectivity and additional options
   

   Table 3 Connectivity

   Parameter	Description
   DB Instance Name	Different DB instances can have the same name. The instance name must start with a letter and consist of 4 to 64 characters. Only letters (case-sensitive), digits, hyphens (-), and underscores (_) are allowed.
   VPC	Same as the primary DB instance's VPC.
   Subnet	Same as the primary instance's subnet. IPv4 address: A floating IPv4 address is automatically assigned when you create a read replica. You can also enter an unused floating IPv4 address in the subnet CIDR block. After the read replica is created, you can change the floating IP address. IPv6 address: A read replica assigned a floating IPv6 address will be created only when the vCPUs and memory you selected support IPv6 addresses. A floating IPv6 address is automatically assigned during read replica creation and cannot be specified. After the read replica is created, this floating IP address cannot be changed.
   Security Group	Same as the primary DB instance's security group.

   Table 4 Additional options

   Parameter	Description
   Enterprise Project	If your account has been associated with an enterprise project, select the target project from the Enterprise Project drop-down list. For more information about enterprise projects, see Enterprise Management User Guide.
   Tag	Optional. Tags help you easily identify and manage your read replicas. A maximum of 20 tags can be added for each read replica. After a read replica is created, you can view its tag details on the Tags page. For details, see Managing Tags.

   Table 5 Yearly/monthly read replicas

   Parameter	Description
   Required Duration	The system will automatically calculate the configuration fee based on the selected required duration. The longer the required duration is, the larger discount you will enjoy.
   Auto-renew	By default, this option is not selected. If you select this option, the auto-renew cycle is determined by the selected required duration.

6. Confirm specifications.
   • If you need to modify your settings, click Previous.
   • If you do not need to modify your settings, click Submit for pay-per-use read replicas.
   • For yearly/monthly read replicas, click Pay Now.

7. After a read replica has been created, you can view and manage it on the Instances page by clicking on the left of the DB instance to which it belongs.

   You can view the detailed progress and result of the task on the Task Center page. For details, see Task Center.

FAQ

Q: Does creating read replicas during peak hours increase the load on my primary instance when my primary instance's CPU usage is high?

A: Yes. When a read replica is created, it synchronizes data from the primary instance, which consumes I/O and CPU resources of the primary instance. To avoid this impact, you can create read replicas during off-peak hours.

Follow-up Operations

Managing a Read Replica