ApsaraDB RDS:Create a read-only SQL Server instance

Prerequisites

Before you begin, ensure that you have:

• A primary instance running SQL Server 2017 EE on RDS Cluster Edition, SQL Server 2019 EE on RDS Cluster Edition, or SQL Server 2022 EE on RDS Cluster Edition

• Instance edition: Cluster Edition

• Instance storage type: Enterprise SSD (ESSD), premium performance disk

• Billing method: Subscription or pay-as-you-go (Serverless instances are not supported)

If your primary instance runs Basic Edition or High-availability Edition, upgrade it to Cluster Edition before proceeding. If you do not have a primary instance, create one that meets the requirements above.

Limits

Billing

Read-only instances are billed by subscription or pay-as-you-go. For pricing details, see Pricing.

If the billing method of the primary RDS instance is serverless, you cannot create read-only RDS instances.

Create a read-only instance

Create a read-only instance from the RDS console or by calling the CreateReadOnlyDBInstance API.

1. Log on to the ApsaraDB RDS console and go to the Instances page. In the top navigation bar, select the region where the primary instance resides. Find the instance and click its ID.

2. In the Instance Distribution section, click Add to the right of Read-only Instance.

1. Configure basic resources, then click Next: Instance Configuration. For details, see Storage classes. Specify the instance family, then configure CPU cores, memory capacity, and maximum connections. Storage capacity includes data space, system file space, log file space, and transaction file space. The available range depends on the instance type and storage type you selected. Adjust in increments of at least 5 GB.

   1. Configure the Storage Capacity.

   Place the read-only instance in the same zone as your Elastic Compute Service (ECS) instance for optimal performance. Instances in different zones within the same region have slightly lower performance.

   Each instance type has a defined set of CPU cores, memory, maximum connections, and maximum IOPS. To maintain I/O performance for data synchronization, set the read-only instance memory to be equal to or greater than the primary instance memory.

   The storage capacity of a read-only instance cannot be less than that of the primary instance. For local SSD instances, storage space is tied to the instance type; this restriction does not apply to ESSDs or standard SSDs.

   Billing method	When to use	Key benefit
   Subscription	Long-term use	More cost-effective than pay-as-you-go for extended periods; lower prices for longer durations. Configure the Subscription Duration in the lower part of the page.
   Pay-as-you-go	Short-term or evaluation use	Billed hourly based on actual usage. Release the instance at any time and billing stops immediately. Switch to subscription after confirming the instance meets your requirements.

   Category	Resource allocation	Key benefit
   General-purpose instance types	Memory and I/O: dedicated. CPU and storage: shared	Cost-effective
   Dedicated instance types	All CPU, memory, storage, and I/O resources: dedicated. The dedicated host instance family exclusively occupies all resources of the host.	Better performance and stability

2. Configure network and instance settings, then click Next: Confirm Order. Select the same VPC as your ECS instance for internal network communication. Instances in different VPCs cannot communicate over the internal network. Instances using different vSwitches in the same VPC can communicate over the internal network.

   1. Configure optional parameters as needed. If you have no special requirements, keep the default values.

   Parameter	Description
   Release Protection	Available for pay-as-you-go instances. Enable release protection to prevent accidental instance deletion.
   Resource Group	Use the default resource group or select a custom one.
   Instance Name	2–255 characters. Allowed: letters, digits, underscores (_), and hyphens (-). Must start with a letter or Chinese character.
   Character Set Collation Rule	Defaults to the primary instance's system collation.

3. Review the Parameter Configuration, Quantity, and Subscription Duration (for subscription instances). Click Confirm Order and complete the payment.

   For subscription instances, enable Auto-renewal to avoid service interruptions. Instance creation takes 1 to 10 minutes. Refresh the page to view the new instance.

View a read-only instance

View read-only instances from any of three locations in the console.

On the Instances page

1. Log on to the RDS console. In the navigation pane, click Instances. In the top navigation bar, select the region.

2. Find the read-only instance and click its ID.

On the Basic Information page of the primary instance

1. Log on to the RDS console. In the navigation pane, click Instances. In the top navigation bar, select the region.

2. Find the primary instance and click its ID.

3. On the Basic Information page, hover over the read-only instance count and click the ID of the target read-only instance.

On the Cluster Management page

Prerequisites: Read/write splitting is enabled on the Cluster Management page. For details, see Enable read/write splitting.

1. Log on to the ApsaraDB RDS console.

2. Find the primary instance and click its ID.

3. In the navigation pane, click Cluster Management.

4. Find the read-only instance and click its ID.

What's next

After the read-only instance is created, enable the read/write splitting endpoint and configure the weight ratio for the read-only address. The system routes read requests based on the configured weight ratio.

FAQ

SELECT
    ag.name AS [availability_group_name]
    , d.name AS [database_name]
    , ar.replica_server_name AS [replica_instance_name]
    , drs.truncation_lsn
    , drs.log_send_queue_size
    , drs.redo_queue_size
FROM
    sys.availability_groups ag
    INNER JOIN sys.availability_replicas ar
        ON ar.group_id = ag.group_id
    INNER JOIN sys.dm_hadr_database_replica_states drs
        ON drs.replica_id = ar.replica_id
    INNER JOIN sys.databases d
        ON d.database_id = drs.database_id
WHERE drs.is_local=0
ORDER BY
    ag.name ASC, d.name ASC, drs.truncation_lsn ASC, ar.replica_server_name ASC