I want to change my reader instance to one that can write and delete the existing writer instance.

Hello, joeylover

It is fully understandable that you are trying to delete the writer instance, and allow the reader instance to perform both reader and writer roles for cutting costs. Unfortunately, RDS and Aurora clusters cannot replace one another once the role of reader and writer instances has been established at the first time. Since the reader instance has been given the role of reader, it has become impossible to write data internally, the reader instance cannot take over the role of the writer instance.

Additionally, when you are using Aurora cluster and have 1 writer instance and 1 reader instance, if you delete a writer instance, the reader instance is converted to a writer instance, resulting in only one writer instance remaining. Therefore, you cannot place only reader instances, or create instances that perform both reader and writer.

I understood the DB connection address of the reader instance that you inquired about as the endpoint of the reader instance. For endpoint of a reader instance, the value is maintained even if you modify the settings associated with the reader instances.

If I have missed anything or answered wrong, please feel free to ask me again. Also you have any questions, comment please!

It is not clear from the question whether the system is an RDS DB with a reader instance, or a DB cluster. Or, whether it is RDS MySQL or RDS Aurora MySQL.

In either case what you wish to achieve can be achieved but the steps would be different.