Changing an Instance Type from Single-Node to Primary/Standby

Scenarios

RDS for PostgreSQL allows you to change an instance type from single-node to primary/standby. This enhances instance reliability while retaining the original instance resources. However, the conversion process affects the primary instance's network I/O and disk I/O.

Instance Architecture

Single-node instances use a standalone architecture. If a fault occurs on a single-node instance, the instance cannot recover in a timely manner.

A primary/standby instance uses a classic HA architecture with a primary node and a standby node. If the primary node fails, the instance automatically performs a failover, allowing the standby node to quickly take over workloads. You are advised to deploy primary and standby instances in different AZs for high availability and disaster recovery. Anti-affinity deployment is supported for primary/standby instances to prevent the entire instance from becoming unavailable due to a single-host failure.

Figure 1 Topology

Precautions

Changing a single-node instance to primary/standby does not change its networking information, including the VPC, subnet, security group, private IP address, private domain name, and database port.

Billing

**Table 1** Billing
Billing Mode	Operation	Impact on Fees
Yearly/Monthly	Changing a single-node 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-node 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-node 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-node 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-node 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 RDS console.
Click in the upper left corner and select a region.
On the Instances page, locate a single-node 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 instance list, click to refresh the list. After the instance type is changed to primary/standby, the instance status will change to Available and the instance type will change to Primary/Standby.