ApsaraDB for RDS offers four editions: Basic Edition, High-availability Edition, Cluster Edition, and Enterprise Edition. This topic describes the Cluster Edition.

The Cluster Edition is developed based on the native SQL Server technology AlwaysOn. Only SQL Server 2017 supports the Cluster Edition. In the Cluster Edition, computing is separated from storage, and you can create read-only instances to implement read/write splitting. After you create read-only instances, you can apply for a read-only routing endpoint. By default, each read-only instance is assigned an independent internal endpoint that is used to connect only to the specified read-only instance.

Note After you enable the read-only routing endpoint, you must add the read-only routing endpoint and the endpoint of the primary instance to your application. This allows your database system to forward write requests to the primary instance and read requests to the read-only routing endpoint.
The Cluster Edition provides one primary instance and one secondary instance by default. You can create up to seven read-only instances later based on your business requirements. The following figure shows the topology of your database system in the Cluster Edition.


  • Scalable read capability
    You can create read-only instances to scale up the read capability of your database system. The specifications of the read-only instances can differ from those of the primary instance. Therefore, you can create read-only instances that have higher specifications than the primary instance. This allows you to increase the read capability of your database system.
    Note The read-only instances do not support the high availability architecture. To ensure high availability, we recommend that you create at least two read-only instances.
  • Flexible cost control

    The read-only instances belong to the general-purpose instance family that delivers high cost-effectiveness. They can offload read requests from the primary instance to optimize the configuration of your database system. In addition, the read-only instances can have lower specifications than the primary instance. You can create such read-only instances to process read requests from background applications, such as intelligent analytics applications.

    The Cluster Edition also supports the maximum performance mode. This mode is under development. In this mode, you can configure asynchronous replication between the primary and secondary instances during peak hours. This allows you to maximize the performance of your database system.


  • Use read-only instances to offload read requests during peak hours

    For example, you can create read-only instances for new retail enterprises. This allows you to process read requests that grow several times during online shopping festivals, such as Double 11. The read-only instances allow you to implement read/write splitting and traffic throttling.

  • Confine analytics tasks to read-only instances

    Enterprises can create an independent read-only instance that uses intelligent methods to analyze data. This reduces the probability of blocked requests on the primary instance, increases the concurrency of transactions, and decreases interruptions to crucial workloads. This way, you can ensure the service stability of your database system.

Create an RDS instance

For more information about how to create an RDS instance that runs the Cluster Edition, see Create an ApsaraDB RDS for SQL Server instance.