This topic describes the architectures, benefits, and scenarios of RDS Cluster Edition for ApsaraDB RDS for SQL Server.
Introduction to RDS Cluster Edition
In RDS Cluster Edition, your database system consists of a primary RDS instance and a secondary RDS instance. These instances work in HA mode. RDS Cluster Edition uses the Always On architecture of native SQL Server to implement compute-storage separation and allows you to create up to seven read-only RDS instances to implement read/write splitting and increase the read capability.
After you create read-only RDS instances for your RDS instance that runs RDS Cluster Edition, 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 to isolate queries.
After you enable read/write splitting for a primary RDS instance that runs RDS 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 forward write requests to the primary RDS instance and read requests to the read-only routing endpoint.
In RDS Cluster Edition, a primary RDS instance and a secondary RDS instance work in HA mode. If the primary RDS instance fails, your workloads are automatically switched over to the secondary RDS instance. This improves service stability.
Read-only RDS instances cannot ensure HA. If the primary RDS instance fails, your workloads cannot be automatically switched over to the read-only RDS instances. No disaster recovery RDS instances are provided for a read-only RDS instance. To ensure business availability and continuity, we recommend that you create at least two read-only RDS instances. If a read-only RDS instance fails, the other read-only RDS instance can continue to provide services.
When you purchase an RDS instance that runs RDS Cluster Edition, we recommend that you select multi-zone deployment to implement cross-zone disaster recovery.
Architecture
RDS Cluster Edition is supported by RDS instances that run SQL Server 2022, SQL Server 2019, and SQL Server 2017. The following figure shows the architecture of RDS Cluster Edition.
Benefits
Scalable read capabilities
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 RDS instance to attain a strong read capability.
Cost-effectiveness
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 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.
Configure the read attribute for a secondary RDS instance
If you purchase an 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 RDS Cluster Edition, the secondary RDS instance becomes readable and serves as a read-only RDS instance by default. This helps reduce the costs of a read-only RDS instance and cloud migration. For more information, see Configure the read attribute for a secondary RDS instance.
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. This helps improve the system performance and response speed.
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 business stability.
Scenarios of RDS Cluster Edition for ApsaraDB RDS for SQL Server
Item | Description |
Configuration of an RDS cluster | |
Upgrade of an RDS instance to RDS Cluster Edition |
Create an RDS instance that runs RDS Cluster Edition
For more information about how to create an RDS instance that runs RDS Cluster Edition, see Create an ApsaraDB RDS instance for SQL Server instance.