You're going to need the unique ID that has been assigned to an RDS read replica. If you followed the Creating a database with automatic failover and Creating a database read replica recipes, then you'll be all set.
It's also a good idea to have backups enabled on this read replica before promoting it. This shortens the promotion process because you won't need to wait for a backup to be taken. You'll want to set the backup retention period to a value between 1 and 8.
Enabling backups on your read replica will cause it to reboot!
To enable backups, you can use the following CLI command:
aws rds modify-db-instance
--db-instance-identifier <identifier-for-read-replica>
--backup-retention-period <days-to-keep-backups-for>
--apply-immediately
You can drop the --apply-immediately parameter if you prefer to wait for the reboot to happen during the configured maintenance window. But you'll still want to wait until after the reboot happens before you continue with the promotion process.
To ensure that you have the most up-to-date data before promotion, you'll want to stop all write traffic to the current source primary DB before going ahead. It's also a good idea to make sure that the replication lag on your read replica is 0 (you can check this in CloudWatch).
To ensure that you have the most up-to-date data before promotion, you'll want to stop all write traffic to the current source primary DB before going ahead. It's also a good idea to make sure that the replication lag on your read replica is 0 (you can check this in CloudWatch).