Creating an HA Read Replica

Scenarios

Read replicas enhance the read capabilities and reduce the load on your DB instances. To create HA read replicas, contact customer service to apply for the required permissions.

After an RDS instance is created, you can create HA read replicas for it as required.

Constraints

• To create HA read replicas, you must have the required permissions. You can contact customer service to apply for the permissions.
• If you are creating an HA read replica, you can select Cloud SSD for Storage Type.
  • Cloud SSD: General-purpose, dedicated, and Kunpeng general-enhanced instance classes are supported.
• If you want to change a single read replica to an HA read replica, the single read replica must use Cloud SSD as its storage type.
  • Cloud SSD: General-purpose, dedicated, and Kunpeng general-enhanced instance classes are supported.

• If you are a DeC user, you can also create HA read replicas or change read replicas to HA read replicas. When you select DSS for Resource Type, only the storage type that you have selected when buying the DSS service is displayed by default.
• When you create an HA read replica, the SSL certificate, disk encryption, port, and subnet of the HA read replica are unconfigurable. They are kept the same as an existing HA read replica, or your primary instance if no HA read replica has been created.
• To change a non-HA read replica to an HA read replica, ensure that the SSL certificate, disk encryption, port, and subnet of the non-HA read replica are the same as an existing HA read replica, or your primary instance if no HA read replica has been created.
• Ensure that the subnet where your instance resides has at least three IP addresses to be assigned to HA read replicas.
• To ensure reliable operation of your workloads, do not modify parameters of HA read replicas.
• For an HA read replica, do not change its port or change it to a non-HA read replica.
• 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.
• Do not perform DDL operations when creating read replicas. Otherwise, creating read replicas may fail.

Creating an HA Read Replica

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 HA read replica.
   Storage Type	The storage type determines the read/write speed of an instance. The higher the maximum throughput is, the higher the read/write speed can be. Cloud SSD: stores data in cloud SSDs to achieve decoupled compute and storage. 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 Specifications

   Parameter	Description
   Instance Class	vCPUs and memory of an instance. Different instance classes support different numbers of database connections and maximum IOPS. After a DB instance is created, you can change its instance class. For details, see Changing a DB Instance Class. DB instances in a DCC only support the general-enhanced instance class.
   Storage Space	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 instance.

   Figure 3 Connectivity and additional options
   

   Table 3 Connectivity

   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 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 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. Using tags can help you easily identify and categorize 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 renew cycle is the same as the selected 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.

   To view the detailed progress and result of the creation, go to 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.

Q: Does an HA read replica can be deployed across AZs?

A: Yes. Although you can select only one AZ when creating an HA read replica, it is deployed across AZs in fact.