ApsaraDB RDS is available in four editions: Basic Edition, High-availability Edition, Cluster Edition, and Enterprise Edition. This topic describes Cluster Edition.

Cluster Edition is supported for SQL Server 2017 and SQL Server 2019. Cluster Edition is developed based on the native SQL Server technology AlwaysOn. In Cluster Edition, computing is separated from storage, and you can create read-only RDS instances to implement read/write splitting. After you create a read-only RDS instance, you can apply for a read-only routing endpoint to implement read/write splitting. By default, each read-only RDS instance is assigned an independent internal endpoint. The internal endpoint of a read-only RDS instance is used to connect only to that read-only RDS instance.

Note After you enable read/write splitting for a primary RDS instance that runs Cluster Edition, you can specify read weights for the primary RDS instance, secondary RDS instance, and read-only RDS instances. After you enable the read-only routing endpoint, you must add the read-only routing endpoint and the endpoint of the primary RDS instance to your application. This way, your database system can route write requests to the primary RDS instance and route read requests to the read-only routing endpoint.
By default, if you use Cluster Edition, your database system consists of a primary RDS instance and a secondary RDS instance. These instances work together in a high-availability architecture. You can create up to seven read-only RDS instances for your database system based on your business requirements. The following figure shows the topology of a database system that runs Cluster Edition.

Benefits

  • Scalable read capability
    You can create read-only RDS instances to linearly increase the read capability of your database system. The specifications of read-only RDS instances can be different from the specifications of the primary RDS instance. You can create read-only RDS instances that have higher specifications than the primary instance to attain a strong read capability.
    Note No secondary RDS instance is provided as a standby for a read-only RDS instance to ensure high availability. To ensure high availability, you must create at least two read-only RDS instances.
  • Flexible cost control

    Read-only RDS instances can use general-purpose and dedicated instance types, which are cost-effective. You can create read-only RDS instances to offload read requests from the primary RDS instance. This helps reduce costs and optimize system configurations. Read-only RDS instances can have lower specifications than the primary RDS instance. You can create read-only RDS instances with low specifications to process read requests from background applications, such as intelligent analytics applications. This way, you can also reduce costs.

  • Configurable read attribute of a secondary RDS instance

    If you purchase an ApsaraDB RDS instance that runs Cluster Edition, a primary RDS instance and a secondary RDS instance are provisioned. You can configure the read attribute for the secondary RDS instance. After you enable read/write splitting for the primary RDS instance that runs Cluster Edition, the secondary RDS instance serves as a read-only RDS instance by default. This helps reduce the cost of cloud migration. For more information, see Configure the read attribute for a secondary RDS instance of a primary ApsaraDB RDS for SQL Server instance.

Use scenarios

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

    For example, you can create read-only RDS instances that have high specifications to help new retail enterprises implement read/write splitting and traffic throttling and process read requests that grow several times during large-scale online promotional events, such as Double 11.

  • Confine analytics tasks to read-only RDS instances.

    An enterprise can create an independent read-only RDS instance that uses intelligent technologies to analyze data. This reduces the probability of blocking on the primary RDS instance, increases concurrency, and mitigates interruptions to crucial workloads to ensure service stability.

Create an RDS instance that runs Cluster Edition

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