Switch workloads over between primary and secondary ApsaraDB RDS for SQL Server instances - ApsaraDB RDS

ApsaraDB RDS for SQL Server provides the primary/secondary switchover feature to ensure high availability. If the primary RDS instance of your database system fails due to system operation errors or hardware failures, the system automatically switches your workloads over from the primary RDS instance to the secondary RDS instance. After the primary/secondary switchover is complete, the secondary RDS instance becomes the new primary RDS instance. The endpoint that is used to connect to your database system remains unchanged. Your application can automatically connect to the new primary RDS instance by using the endpoint. This ensures high availability. You can also manually switch your workloads over between the primary and secondary RDS instances when you need to upgrade, maintain, or troubleshoot your database system.

Prerequisites

The primary RDS instance runs RDS High-availability Edition or RDS Cluster Edition.

Note

If you use RDS Cluster Edition, only automatic primary/secondary switchovers are supported. You cannot manually switch workloads over between primary and secondary RDS instances. If you want to manually switch workloads over between primary and secondary RDS instances, contact Alibaba Cloud technical support.
If you want to manually switch workloads over between primary and secondary RDS instances, contact Alibaba Cloud technical support.

Feature description

Automatic primary/secondary switchover: By default, the automatic primary/secondary switchover feature is enabled. If the primary RDS instance fails, the system automatically switches your workloads over to the secondary RDS instance. For more information about the causes of primary/secondary switchovers, see Reasons for primary/secondary switchovers.
Manual primary/secondary switchover: You can manually switch your workloads over between the primary RDS instance and the secondary RDS instance even if the automatic primary/secondary switchover feature is enabled. You can perform manual primary/secondary switchovers for disaster recovery drills. You can also perform manual primary/secondary switchovers if you use the multi-zone deployment method and want to connect your application to the RDS instance in the zone that is closest to your application.

Note

Data is synchronized between the primary RDS instance and the secondary RDS instance in real time. You can access only the primary RDS instance. The secondary RDS instance runs only as a standby.

Limits

Serverless RDS instances do not support manual primary/secondary switchovers. For more information, see Overview. If a serverless RDS instance fails, the system automatically switches workloads over between primary and secondary serverless RDS instances.

Usage notes

A service interruption that lasts approximately 30 to 120 seconds occurs during a primary/secondary switchover. Make sure that your application is configured to automatically reconnect to your database system.
After a primary/secondary switchover, the read-only RDS instances that are attached to the primary RDS instance must re-establish the connections that are used to replicate data to and synchronize incremental data from the primary RDS instance. As a result, the data on the read-only RDS instances shows latencies of a few minutes.
The primary/secondary synchronization mechanism of ApsaraDB RDS for SQL Server ensures full data synchronization between the primary RDS instance and secondary RDS instance of your database system. However, not all parameter settings of the ALTER LOGIN statement are synchronized. Only the settings of the SID, login_name, and password parameters in the ALTER LOGIN statement are synchronized. ApsaraDB RDS for SQL Server uses the default values for all the other parameters in the ALTER LOGIN statement. For more information, see ALTER LOGIN (Transact-SQL).

Impacts

A service interruption that lasts approximately 30 to 120 seconds occurs during a primary/secondary switchover. Make sure that your application is configured to automatically reconnect to your database system.
After a primary/secondary switchover, the read-only RDS instances that are attached to the primary RDS instance must re-establish the connections that are used to replicate data to and synchronize incremental data from the primary RDS instance. As a result, the data on the read-only RDS instances shows latencies of a few minutes.
A primary/secondary switchover does not cause changes to the endpoints that are used to connect to your RDS instance. However, the IP addresses that are associated with the endpoints may change. If your application uses endpoints to connect to your RDS instance, your application can still run as expected after a primary/secondary switchover.

Perform a manual primary/secondary switchover

Go to the Instances page. In the top navigation bar, select the region in which the RDS instance resides. Then, find the RDS instance and click the ID of the instance.
In the left-side navigation pane of the page that appears, click Service Availability.
In the Availability Information section of the page that appears, click Switch Primary/Secondary Instance.
Specify the time at which you want to perform a primary/secondary switchover. Then, click OK.
Note
You cannot perform specific operations during a primary/secondary switchover. For example, you cannot manage databases and accounts or change the network type. We recommend that you select Within Specified Time Range.

Disable automatic primary/secondary switchovers for a short period of time

Scenarios

By default, the automatic primary/secondary switchover feature is enabled. If the primary RDS instance fails, the system automatically switches your workloads over from the primary RDS instance to the secondary RDS instance. You can temporarily disable the automatic primary/secondary switchover feature in the following situations:

A large-scale sales promotion during which you do not want a primary/secondary switchover to affect system availability
An important application upgrade during which you do not want a primary/secondary switchover to cause unexpected issues
A major event during which you do not want a primary/secondary switchover to affect system stability

Procedure

Go to the Instances page. In the top navigation bar, select the region in which the RDS instance resides. Then, find the RDS instance and click the ID of the instance.
In the left-side navigation pane of the page that appears, click Service Availability.
In the Availability Information section, click Automatic Primary/Secondary Switchover.
Note
If you cannot find Automatic Primary/Secondary Switchover, check whether the primary RDS instance meets all prerequisites.
Select Temporarily Disable, configure the Deadline parameter, and then click OK.
Note
- When the date and time specified by the Deadline parameter arrives, the automatic primary/secondary switchover feature is automatically enabled.
- If you do not configure the Deadline parameter, the automatic primary/secondary switchover feature is disabled for one day by default. You can set the Deadline parameter to 23:59:59 seven days later at most.

After the configuration is complete, you can check the deadline after which the automatic primary/secondary failover feature is automatically enabled on the Service Availability page.

View primary/secondary switchover logs

Note

You can view primary/secondary switchover logs only when the primary RDS instance runs SQL Server 2008 R2 with local disks.

Go to the Instances page. In the top navigation bar, select the region in which the RDS instance resides. Then, find the RDS instance and click the ID of the instance.
In the left-side navigation pane of the page that appears, click Service Availability.
In the Primary/Secondary Switching Logs section of the page that appears, select a time range and view the primary/secondary switchover logs that are generated over the selected time range.

FAQ

Do I need to manually switch my workloads over from the secondary RDS instance to the primary RDS instance after a primary/secondary switchover?
No, you do not need to manually switch your workloads over from the secondary RDS instance to the primary RDS instance after a primary/secondary switchover. The data in the primary RDS instance is the same as the data in the secondary RDS instance. After a primary/secondary switchover, the secondary RDS instance serves as the new primary RDS instance. No additional operations are required.
Each time a primary/secondary switchover is performed, my RDS instance does not run as expected 10 minutes after the primary/secondary switchover is complete. What are the possible causes? How do I handle the issue?
If an exception on your RDS instance triggers a primary/secondary switchover to ensure high availability, your application may fail to identify and respond to the changes to the connections. If no timeout periods are specified for socket connections, your application waits for the database to return the results. In most cases, your application is disconnected after hundreds of seconds. During this period, some connections to the database cannot work as expected, and a large number of SQL statements fail to be executed. To avoid invalid connections, we recommend that you configure the connectTimeout and socketTimeout parameters to prevent your application from waiting for a long period of time due to network errors. This reduces the time required to recover from failures.
You must configure these parameters based on your workloads and usage modes. For online transactions, we recommend that you set the connectTimeout parameter to 1 to 2 seconds and the socketTimeout parameter to 60 to 90 seconds. This configuration is for reference only.

Related operations

Operation	Description
SwitchDBInstanceHA	Switches workloads over between primary and secondary instances.
ModifyHASwitchConfig	Enables or disables the automatic primary/secondary switchover feature for an instance.
DescribeHASwitchConfig	Queries the settings of the automatic primary/secondary switchover feature for an instance.