How to change a RDS instance class on master instance with a read replica?

Question

I would like to change a RDS Instance class and also change the RDS instance class to its replica. I read in the AWS Documentation that read replica becomes a standalone instance when Master (source) instance goes down. I also read that Modifying Instance Class requires a requires a reboot. So, if the reboot happens on the master instance (during the time it is unavailable), Read replica might take over and become a Standalone instance which I don't intend to happen. Should I stop read replica when I change the instance class on master instance? What are the steps to make sure Read replic continues after the instance class is changed both on Master Instance and read replica?

Below, I composed a set of steps based on the documentation but i'm not sure if this is the right approach: 1. Stop RDS replica-test-1 (reader) 2. Change instance class to db.r4.large on master RDS test-1 and let the status change to “available” 3. Reboot master RDS test-1 and see that it is available again 4. Start RDS replica-test-1 (reader) 5. Change instance class to db.r4.large on replica-test-1 and let the status change to “available” 6. Reboot replica-test-1 and see that it is available again.

Could someone please help me know if this is the right approach?

Answer 1

You can also try to enable Multi A-z deployment for both master and slaves where the master and slave will be available even if it is rebooted multiple times.

Answer 2

I read in the AWS Documentation that read replica becomes a standalone instance when Master (source) instance goes down.

You have misinterpreted something. This is a description of what happens when you promote a read replica to master. This is a deliberate administrative action you do. The service never does this automatically, in RDS for MySQL or MariaDB.

None of your proposed steps is necessary. Just modify the master server. The replica will not be promoted when the master reboots.