Creating a 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 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 of the page and choose Databases > Relational Database Service.
3. On the Instances page, locate the target DB instance and choose More > Create Read Replica in the Operation column.
4. On the displayed page, configure required parameters and click Buy.

   Table 1 Basic information

   Parameter	Description
   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.
   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 or Ultra-high I/O Stores data in cloud disks for decoupled storage and compute. The maximum throughput is 350 MB/s. For RDS for MySQL instances, this storage type is normally displayed as Cloud SSD, but for existing instances in certain regions it is displayed as Ultra-high I/O. Extreme SSD Uses 25GE network and RDMA technologies to provide you with up to 1,000 MB/s throughput per disk and sub-millisecond latency.
   AZ	RDS allows you to deploy your DB instance and read replicas in the same AZ.

   Table 2 Specifications and storage

   Parameter	Description
   Instance Class	Refers to the vCPUs and memory of a DB instance. Different instance classes support different numbers of database connections and maximum IOPS.
   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 enhances data security but reduces the database's read and write performance by 5%. 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 the "Creating a Key" section in the Data Encryption Workshop User Guide.

   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	Same as the primary DB 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.
   Security Group	Same as the primary DB instance's security group.

   Table 4 Additional Options

   Parameter	Description
   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 RDS for MySQL 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-renewal cycle is determined by the selected required duration.

5. 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.

6. After a read replica is created, 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