RDS Aurora MySQL 5.6 -> 5.7 upgrade stalled

Please open a ticket with support, as they have access to backplane and logs, without access to logs, its very hard to figure out what exactly is going on. How big is the database, Major version upgrade does take several hours to complete.

The best way to proceed forward is to follow up with support as was initially suggested, but here is what is likely happening. Aurora MySQL performs a clean shutdown for the writer DB instance during the upgrade and progress events are recorded every 15 minutes for operations where Aurora purges the undo records for old versions of rows and rolls back any uncommitted transactions. MySQL maintains a history of all undo changes and this "list" can be quite long depending on a number of factors like long running transactions. You can read about the Global History functionality of InnoDB in the link provided below

https://blog.jcole.us/2014/04/16/the-basics-of-the-innodb-undo-logging-and-history-system/.

The command "SHOW ENGINE INNODB STATUS" can give you some information about the length of this list.
Reducing the size of this list and the UNDO records prior to upgrading will reduce the amount of time that Aurora needs to purge these records during the upgrade. As was mentioned, our support team can provide more guidance.

In addition to the advice my colleagues have provided, this Knowledge Center Article has more information about purge and undo records.