Changing a DB Instance Type from Single to Primary/Standby

Scenarios

RDS enables you to change single DB instances to primary/standby DB instances to improve instance reliability. This operation affects network and disk I/O operations of the primary DB instance.
Primary/standby DB instances support automatic failover. If the primary DB instance fails, the standby DB instance takes over services quickly. You are advised to deploy primary and standby DB instances in different AZs for high availability and disaster recovery.
Anti-affinity deployment is supported for primary/standby DB instances to prevent the entire instance unavailability due to the failure of a single host.

Precautions

RDS single DB instances can be changed to primary/standby DB instances, but not the other way around. You can use Data Replication Service (DRS) or the export and import tool of the client to migrate data from primary/standby DB instances to single DB instances.

Billing

**Table 1** Billing
Billing Mode	Operation	Impact on Fees
Yearly/Monthly	Changing a single DB instance to primary/standby	You need to pay for the difference in price based on the remaining period. The following prices are for reference only. The actual prices are subject to the price displayed on the console. Suppose you purchased a one-month RDS for PostgreSQL 14 single DB instance (instance class: general-purpose, 2 vCPUs \| 8 GB; storage: cloud SSD, 40 GB) in CN-Hong Kong on June 1, 2023. The instance price was $59.56 USD per month. On June 15, 2023, you changed the instance type from single to primary/standby. The instance price became $155.69 USD per month. Price difference = Price for the primary/standby instance × Remaining period - Price for the single instance × Remaining period The remaining period is the remaining days of each calendar month divided by the maximum number of days in each calendar month. In this example, the remaining period and price difference are calculated as follows: Remaining period = 15 (Remaining days in June)/30 (Maximum number of days in June) = 0.5 Price difference = $155.69 USD x 0.5 - $59.56 USD x 0.5 = $48.06 USD
Pay-per-use	Changing a single DB instance to primary/standby	The primary/standby DB instance is billed by hour. For details, see Product Pricing Details.

Procedure

Log in to the management console.
Click in the upper left corner and select a region.
Click in the upper left corner of the page and choose Databases > Relational Database Service.
On the Instances page, locate a single DB instance and choose More > Change Type to Primary/Standby in the Operation column.
Select a standby AZ. Other configurations are the same as those of the primary DB instance by default. Confirm the configurations and click Submit.

It is recommended that the standby AZ be different from the primary AZ to provide failover and high availability.
Check the instance status on the Instances page.
- The DB instance is in the Changing type to primary/standby status. You can view the progress on the Task Center page. For details, see Task Center.
- In the upper right corner of the DB instance list, click to refresh the list. After the DB instance type is changed to primary/standby, the instance status will change to Available and the instance type will change to Primary/Standby.