ApsaraDB for MongoDB:Why does ApsaraDB for MongoDB trigger primary/secondary switchover?

Notification example

[Alibaba Cloud] Dear \*\*\*\*: Your ApsaraDB for MongoDB instance dds-bp\*\*\*\* (name: \*\*\*\*) has an error. A switchover is triggered to ensure stable running of your instance. We recommend that you check whether your application is still connected to your instance and configure your application to automatically reconnect to your instance.

How it works

A replica set instance has three nodes by default. Each shard in a sharded cluster instance also has three nodes. Primary and secondary nodes handle application connections, while hidden nodes serve as standby targets for switchover. For more information, see Replica set instances or Sharded cluster instances.

Why a switchover was triggered

Two conditions can trigger a primary/secondary switchover:

• Node unavailable: The node health monitoring system detects that a node is not responding and promotes a hidden node to primary.

• Host offline: An exception occurs on the host running the primary node. The HA system switches to a healthy host to prevent extended downtime.

Impact of a switchover

• The switchover causes a transient connection interruption of less than 30 seconds.

• If your application connects directly to the primary node endpoint, read/write operations are affected during the switchover window.

What to do

For immediate reconnection issues: Configure your application to reconnect automatically after a disconnection. Most MongoDB drivers support automatic reconnection by default.

For production environments: Use a connection string URI to connect to the instance, so your application fails over to a healthy node automatically — keeping read/write operations available even when the primary switches. For more information, see Connect to a replica set instance or Connect to a sharded cluster instance.