The following figure illustrates the use of SQL Server AlwaysOn Availability Group (AOAG) in high availability (HA-High Availability) and disaster recovery (DR-Disaster Recovery). Generally speaking, HA nodes will be located in the same data center. Since the network latency is relatively low in the same subnet, synchronous data replication settings are usually adopted. As for the DR node, if it is set in data centers of different subnets, the network delay will be higher, so data replication generally adopts asynchronous settings.
If AOAG is set in a multisubnet environment (such as multiple data centers), in the URL (connection string) parameter of the application ODBC or JDBC, remember to add "MultiSubnetFailover=True" to ensure that the client is in After the failover event occurs, quickly try to reconnect the database.
If AOAG is only set in a single data center (single subnet), this parameter setting can also speed up the client's attempt to reconnect to the database after a failover event occurs.