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

Only SQL Server 2017 supports ApsaraDB RDS Cluster Edition. 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 read-only RDS instances, you can apply for a read-only routing endpoint. 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 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 differ 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 instance types, which are cost-effective. You can create general-purpose 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.

    Cluster Edition supports the maximum performance mode. This mode is in development and will be available in the future. In this mode, you can configure asynchronous replication between the primary RDS instance and the secondary RDS instance during peak hours to maximize the performance of your database system.

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 promotions, 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.