AWS RDS read replicas interaction with application

Question

I am very new to cloud computing. I have never worked with MySQL outside of 1 instance. I am trying to understand how AWS RDS read replicas work with my application. For example say I have 1 master and 2 read replicas. I then from my application server send the query to AWS:

SELECT * FROM users where username = 'bob';

How does this work now? Do I need to include more into my code to choose a certain read replica or does AWS automatically reroute the request or how does it work?

Answer 1

Amazon does not currently provide any sort of load balancing or other traffic distribution across RDS servers. When you send queries to the primary RDS endpoint, 100% of that traffic goes to the primary RDS server. You would have to architect your system to open connections to each server and distribute the queries across the different database servers.

To do this in a way that is transparent to your application, you could setup an HAProxy instance between your application and the database that manages the traffic distribution.

Use of Elastic Load Balancers to distribute RDS traffic is an often requested feature, but Amazon has given no indication that they are working on this feature at this time.