It was mentioned in the video that replica is for boosting performance only but not for disaster recovery but the quiz and also the aws reference page " https://aws.amazon.com/rds/faqs/#Read_Replicas" is telling differently, which says "You may use a read replica for disaster recovery of the source DB instance, either in the same AWS Region or in another Region." Please clarify.
In addition to using Read Replicas to reduce the load on your source DB instance, you can also use Read Replicas to implement a DR solution for your production DB environment. If the source DB instance fails, you can promote your Read Replica to a standalone source server. Read Replicas can also be created in a different Region than the source database. Using a cross-Region Read Replica can help ensure that you get back up and running if you experience a regional availability issue.
An important metric to monitor with a Read Replica is the replica lag, which is the amount of time that the replica is behind the source database. A replica lag can impact your recovery. Replica lag can vary based on the network latency between the source and destination Regions. It can also be affected by the amount of traffic that is being replicated. Because Read Replicas have a running DB instance, the time required to recover after a disaster is lower. However, using Read Replicas in this way is generally a more expensive option than using automated backups or database snapshots.
as I understood, main purpose of read replica is boosting performance of read operations. But replica is an exact copy of your primary db, so no one can stop you from using it if something is wrong with your primary db. Just only thing: you should manually promote it to primary – and you’re back online. With mutli AZ – AWS would switch to secondary automatically no manual action required.
Thus, "can replica be technically used for disaster recovery? " – yes, with manual actions, but it can be used.