Failover process for an RDS Custom for SQL Server Multi-AZ deployment
If a planned or unplanned outage of your DB instance results from an infrastructure defect, Amazon RDS automatically switches to a standby replica in another Availability Zone if you have turned on Multi-AZ. The time that it takes for the failover to complete depends on the database activity and other conditions at the time that the primary DB instance became unavailable. Failover times are typically 60 – 120 seconds. However, large transactions or a lengthy recovery process can increase failover time. When the failover is complete, it can take additional time for the RDS console to show the new Availability Zone.
Note
You can force a failover manually when you reboot a DB instance with failover. For more information on rebooting a DB instance, see Rebooting a DB instance
Amazon RDS handles failovers automatically so you can resume database operations as quickly as possible without administrative intervention. The primary DB instance switches over automatically to the standby replica if any of the conditions described in the following table occurs. You can view these failover reasons in the RDS event log.
| Failover reason | Description |
|---|---|
|
A failover was triggered during the maintenance window for an OS patch or a security update. For more information, see Maintaining a DB instance. |
|
The Multi-AZ DB instance deployment detected an impaired primary DB instance and failed over. |
|
RDS monitoring detected a network reachability failure to the primary DB instance and triggered a failover. |
|
A DB instance modification triggered a failover. For more information, see Modifying an RDS Custom for SQL Server DB instance. |
|
The Multi-AZ DB instance deployment detected a storage issue on the primary DB instance and failed over. |
|
The RDS Custom for SQL Server Multi-AZ DB instance was rebooted with failover. For more information, see Rebooting a DB instance. |
|
The primary DB instance is unresponsive. We recommend that you try the following steps:
|
To determine if your Multi-AZ DB instance has failed over, you can do the following:
Set up DB event subscriptions to notify you by email or SMS that a failover has been initiated. For more information about events, see Working with Amazon RDS event notification.
View your DB events by using the RDS console or API operations.
View the current state of your RDS Custom for SQL Server Multi-AZ DB instance deployment by using the RDS console, CLI, or API operations.
Time to live (TTL) settings with applications using an RDS Custom for SQL Server Multi-AZ deployment
The failover mechanism automatically changes the Domain Name System (DNS) record of the DB instance to point to the standby DB instance. As a result, you need to re-establish any existing connections to your DB instance. Ensure that any DNS cache time-to-live (TTL) configuration value is low, and validate that your application will not cache DNS for an extended time. A high TTL value might prevent your application from quickly reconnecting to the DB instance after failover.