Necessity of having two instances (Reader and Writer) in Amazon Aurora I'm managing an Amazon Aurora account. Somebody set it up months ago.
The service has TWO instances (same AZ):
- project
- project-eu-central-1b

Same class (db.t2.small), but different "Replication Role". First is Reader and the second is Writer. The service has only one cluster:project-cluster-1

I wouldn't like paying twice if I need only one instance but I'm not sure if Aurora actually needs two instances (W and R) to work or it was a bad initial setup.

Can I use one instance for reading/writing and "move permissions" on MySQL-side?
I'm also interested in "Reserved instances". In actual scenario I think I need to buy two reserved instances, right? 

Thanks.
Yes, you are paying twice for the instances, but only once for the storage, because they share a single Aurora cluster storage volume (there is only one volume per cluster), which is part of why replication is nearly instantaneous. 

You can remove the reader instance, as long as you understand that this will slow down recovery if the lone remaining instance fails -- Aurora will have to spin up a new one, instead of automatically promoting the reader to become a writer, which is what it would otherwise do if the current writer fails.