How to create a read-only instance in SQL Server?

To create a read-only instance in SQL Server, you typically set up a secondary replica that is configured for read-only access. This is often done using Always On Availability Groups, which allow you to create a high-availability and disaster-recovery solution while also providing a read-scale-out capability.

Here’s how you can create a read-only instance:

1. Set Up Always On Availability Groups:

   • Ensure that your SQL Server environment is set up for Always On Availability Groups. This requires a Windows Server Failover Cluster (WSFC) and at least two SQL Server instances.
   • Configure the primary replica and one or more secondary replicas.

2. Configure the Secondary Replica for Read-Only Access:

   • During the setup of the secondary replica, you can configure it to allow read-only access. This is done by setting the Readable Secondary option to Yes when configuring the replica.
   • You can also configure the secondary replica to allow read-only routing, which directs read-only queries to the secondary replica.

3. Create an Availability Group Listener:

   • An availability group listener is a DNS name that clients use to connect to the availability group. It automatically routes connections to the primary replica for write operations and to the secondary replicas for read-only operations.
   • Configure the listener to support read-only routing.

4. Connect to the Read-Only Instance:

   • Clients can connect to the read-only instance by using the availability group listener and specifying the ApplicationIntent=ReadOnly parameter in the connection string. This ensures that the connection is routed to a read-only replica.

Example:

-- Connection string for a read-only instance
Server=your-ag-listener;Database=your-database;Integrated Security=SSPI;ApplicationIntent=ReadOnly;

In a cloud environment, you can leverage managed database services that support read-only instances. For example, Tencent Cloud's Managed Database for SQL Server provides high availability and read-only replica capabilities, allowing you to easily set up and manage read-only instances without the complexity of configuring Always On Availability Groups manually. This service simplifies the process and ensures high performance and reliability for your database workloads.