FAQ about instance migration - - Alibaba Cloud Documentation Center

To provide a better user experience and improve service performance and stability, Alibaba Cloud migrates instances from time to time. The system migrates some of your instances to new server nodes to upgrade software, hardware, and network facilities. This topic provides answers to frequently asked questions about instance migration.

Impacts of instance migration events

Point in time	Description	Impact
Migration task creation time	Alibaba Cloud notifies you of the schedule of the migration task by text message, phone call, email, or internal message.	No impact.
Start time Note The start time of a task is automatically generated based on the scheduled switchover time.	The system starts to perform operations related to instance migration, such as applying for new instance resources and synchronizing data.	You can use the database service, but cannot perform instance-level operations, such as changing the configurations of the instance and migrating the instance across zones. You cannot modify the scheduled switchover time while the system is performing the migration task.
Scheduled switchover time	The system switches your workloads to the destination instance.	The instance experiences a transient connection and stays in the read-only state for up to 30 seconds to wait till all data is synchronized. Upgrade the instance during off-peak hours and make sure that your application can automatically reconnect to the instance. Important If the instance uses the cluster or read/write splitting architecture, each shard involved in a switchover experiences a transient connection and stays in the read-only state for up to 30 seconds. Data Management (DMS) and Data Transmission Service (DTS) are temporarily affected. After the switchover is complete, these services return back to normal.
Migration completion time	The task related to the instance is removed from the scheduled events.	No impact. The zone, account, network, and endpoint of the instance are unaffected.

FAQ about start time and scheduled switchover time

How long in advance is a notification about a migration task sent?
The system sends a notification at least 40 hours in advance. After the scheduled switchover time starts, the system switches workloads to the destination instance within the upcoming maintenance window. You can change the switchover time to meet your business requirements. For more information, see View and manage scheduled events.
How do I modify the scheduled switchover time?
You can modify the scheduled switchover time in the Tair console or by calling the related API operation. For more information, see View and manage scheduled events and ModifyActiveOperationTask.
Why am I unable to modify the scheduled switchover time?
If the migration operation has already started, you cannot modify the scheduled switchover time.
Can I estimate the end time of a migration task?
Only the start time of the migration is displayed. The end time cannot be estimated because it is affected by multiple factors, such as the network latency, task queue, and data size.

Other FAQ

Why are instances migrated?
To provide a better user experience and improve service performance and stability, Alibaba Cloud migrates instances from time to time. The system migrates some of your instances to new server nodes to upgrade software, hardware, and network facilities.
Can instances be migrated across zones?
No, instances can only be migrated within the current zone.
Can I cancel an instance migration task?
You cannot cancel the migration task because the instance migration is a task of high urgency. However, you can reschedule the switchover time. For example, you can select a point in time during off-peak hours to perform the switchover.
Are data shards or proxy nodes in a cluster or read/write splitting instance switched over in parallel?
- The data shards are switched over in parallel.
- The proxy nodes are switched over in parallel. A maximum of half of proxy nodes in the instance can be concurrently switched over.
How does the system handle a failed switchover?
Within 1 minute after the switchover is performed, the system checks whether the switchover is successful. If the switchover fails, the system waits for a while and then re-initiates the switchover.
How do I confirm whether an instance migration task is completed?
After an instance migration task is completed, the task is removed from the scheduled events. You can create alert rules. This enables CloudMonitor to monitor tasks and send notifications to you when tasks are completed. For more information, see Alert settings.
Why are two switchovers involved during an instance migration event?
In most cases, an O&M task for an instance requires only one switchover, which occurs at the scheduled switchover time. However, if the instance is deployed across two zones, a second switchover takes place within 120 minutes after the first one to switch the master node back to its original primary zone. This ensures that the instance is located in the same data center as the other services or applications that it interacts with. You do not need to perform any operations during this process. The interval between the two switchovers depends on the speed at which the new replica node is rebuilt after the first switchover.