Creating a Read Replica

Scenarios

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

Constraints

• Up to 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 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.
• 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 and a project.
3. Click in the upper left corner of the page and choose Database > Relational Database Service.
4. On the Instances page, locate the target DB instance and click Create Read Replica in the Operation column.
5. On the displayed page, configure required parameters and click Next.

   Table 1 Basic information

   Parameter	Description
   Region	By default, read replicas are in the same region as your DB instance.
   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.
   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.
   Storage Type	Determines the DB instance read/write speed. A higher maximum throughput enables faster I/O operations. Cloud SSD: cloud drives used to decouple storage from compute.
   AZ	RDS allows you to deploy your DB instance and read replicas in a single AZ or across AZs to improve reliability.

   Table 2 Specifications and storage

   Parameter	Description
   Instance Class	An instance class determines the vCPUs and memory of a DB 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.
   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	If you deselect this option, disk encryption is disabled. If you select this option, disk encryption is enabled. Enabling disk encryption improves security but affects system performance. If you select Enable, the Key Name parameter is displayed. You can select an existing key or create a new one as the tenant key. 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.

   Table 3 Basic settings and network

   Parameter	Description
   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. 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 DB instance 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.
   Enterprise Project	If your account has been associated with an enterprise project, select the target project from the Enterprise Project drop-down list.

   Table 4 Tags

   Parameter	Description
   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 RDS for MySQL Tags.

6. Confirm specifications.
   • If you need to modify your settings, click Previous.
   • If you do not need to modify your settings, click Submit.

7. After the 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, go to the Task Center page.

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