After you create a Global Active Database (GAD) instance group, you can add a secondary instance to it — either by creating a new RDS for PostgreSQL instance or by joining an existing one. You can also remove the secondary instance at any time. A removed instance keeps running as a standalone RDS for PostgreSQL instance; it is not deleted.
Prerequisites
Before you begin, make sure that:
A GAD instance group has been created. For more information, see Create and delete a GAD instance group
The GAD instance group is in the Running state
The GAD instance group is in one of the supported regions: China (Hangzhou), China (Shanghai), China (Beijing), China (Zhangjiakou), China (Shenzhen), China (Hohhot), China (Heyuan), or China (Chengdu)
Impact on the primary instance
Adding a secondary instance triggers an immediate restart of the primary instance. During the restart, which takes approximately 5 to 15 minutes, database connections briefly drop — your business may be interrupted for 10 to 30 seconds.
Plan this operation during a low-traffic maintenance window to minimize impact.
Usage notes
A GAD instance group supports exactly one primary instance and one secondary instance.
Each RDS for PostgreSQL instance can belong to only one GAD instance group, as either the primary or secondary instance.
To release or unsubscribe from a secondary instance, first remove it from the GAD instance group.
Billing
When you use GAD, you are charged for:
The RDS instance used as the secondary instance (only when you create a new instance; no charge if you add an existing one)
The DTS data synchronization between the primary and secondary instances
For details, see Billing.
Add a secondary instance
Two methods are available:
Method 1 — Create a new RDS for PostgreSQL instance and add it as the secondary instance.
Method 2 — Add an existing RDS for PostgreSQL instance as the secondary instance.
Adding a secondary instance restarts the primary instance immediately. Database connections drop for 10 to 30 seconds during the restart process (approximately 5 to 15 minutes total).
Method 1: Create a new instance as the secondary instance
Log in to the RDS console and go to the Global Active Instances page.
In the Actions column for the target instance group, click Add Secondary Instance.
You can also click Add Secondary Instance on the details page of the GAD instance group.
Configure the new RDS for PostgreSQL instance. The instance must meet the following requirements: For all other parameters, see Create an ApsaraDB RDS for PostgreSQL instance.
Parameter Requirement Notes Billing method Subscription or pay-as-you-go — Major engine version Same as the primary instance — Instance type — Dedicated 4 cores and 8 GB of memory or higher — Instance type — General-purpose 2 cores and 4 GB of memory or higher — Storage capacity Greater than or equal to the total storage capacity of the primary instance Check the primary instance's total storage capacity in Basic Information > Instance Resources Configure the Data Transfer Service (DTS) data synchronization task. Keep the default values:
Data Synchronization Type: One-way Synchronization (only option)
Data Synchronization Scope: Instance Synchronization (only option)
Review the configuration and fees, then click Pay Now. In the confirmation dialog, click OK. The system creates the RDS for PostgreSQL instance as the secondary instance and sets up the DTS synchronization task between the primary and secondary instances.
After payment, you are redirected to the GAD instance group details page. Once the secondary instance is added, you can view the instance and the DTS synchronization task on this page. For more information, see View the information about a GAD instance group.
Method 2: Add an existing instance as the secondary instance
Before you add an existing instance, confirm it meets the following requirements. If the instance type or storage capacity does not meet the requirements, change the instance specifications first.
| Parameter | Requirement | Notes |
|---|---|---|
| Billing method | Subscription or pay-as-you-go | — |
| Major engine version | Same as the primary instance | — |
| Instance edition | Same as the primary instance; only Basic Edition and High-availability Edition are supported | — |
| Instance type — Dedicated | 4 cores and 8 GB of memory or higher | Check on the instance's Basic Information page |
| Instance type — General-purpose | 2 cores and 4 GB of memory or higher | Check on the instance's Basic Information page |
| Storage capacity | Greater than or equal to the total storage capacity of the primary instance | Check on the instance's Basic Information page |
Log in to the RDS console and go to the Instances page. Select the region of the existing instance from the top navigation bar, then click the instance ID.
In the upper-right corner of the instance details page, click Add to GAD Cluster.
In the dialog that appears, configure the following parameters:
Parameter Description Region Select the region of the GAD instance group GAD Cluster (Name/ID) Select the GAD instance group Click OK. You are redirected to the GAD instance group details page. Once the secondary instance is added, you can view the instance and the DTS synchronization task on this page. For more information, see View the information about a GAD instance group.
Remove a secondary instance
Removing a secondary instance is separate from releasing or unsubscribing from it. If you want to promote the secondary instance to the primary instance instead, see Promote the secondary instance to the primary instance.
What happens after removal:
The DTS synchronization task between the primary and secondary instances stops.
The removed instance keeps running independently and switches from read-only state to read/write state.
The instance is visible on the Instances page and retains all its data.
The instance can be added to another GAD instance group as a secondary instance if it meets the requirements.
To release or unsubscribe from the secondary instance, remove it from the GAD instance group first, then release or unsubscribe from it. After release, the instance moves to the recycle bin and is permanently deleted after the retention period expires.
Steps:
Log in to the RDS console and go to the Global Active Instances page.
Click the ID of the GAD instance group.
In the List of RDS instances section at the bottom of the page, click Remove in the Actions column for the secondary instance.
In the confirmation message, click Delete.
The connection to the secondary instance and its databases is not interrupted during the removal process. After removal, the instance can be added to another GAD instance group as a secondary instance if it meets the requirements.