Creating a Single Read Replica

Scenarios

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

Constraints

• A maximum of 10 read replicas can be created for a DB instance.
• Ensure that the subnet where your instance resides has at least two IP addresses to be assigned to single read replicas.
• The instance class of a read replica must be no smaller than that of the primary DB instance. Otherwise, the read replica creation may fail or the replication delay may increase.
• For details about how to create read replicas in batches, see Creating Read Replicas in Batches.
• Do not perform DDL operations when creating read replicas. Otherwise, creating read replicas may fail.

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 required parameters 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 your DB instance by default and cannot be changed.
   Replica Type	Select Read replica.
   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 Instance configuration
   

   Table 2 Instance specifications

   Parameter	Description
   Instance Class	Refers to the CPU 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 instance class (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 the 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 Network

   Parameter	Description
   DB 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	Select the same subnet as the primary DB instance or another subnet in the same VPC. For details about how to create a subnet, see Creating a Subnet for the VPC. 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: You can create a read replica using a floating IPv6 address only when the vCPU 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 is created, you can view and manage it.

   For details about how to manage read replicas, see Managing a Read Replica.

   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