Inquiry on Different Connection Pool Settings for RDS Proxy with Aurora PostgreSQL

Hello.

Could you confirm if my understanding and calculations are correct regarding how RDS Proxy manages the connection limits for both the Read-Write and Read-Only endpoints in this configuration?

Yes, I think your calculations are correct.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/rds-proxy-endpoints.html#rds-proxy-endpoints-reader

The more reader DB instances that you have in the cluster, the more simultaneous connections you can make using reader endpoints. For example, suppose that your cluster has four reader DB instances, each configured to support 200 simultaneous connections. Suppose also that your proxy is configured to use 50% of the maximum connections. Here, the maximum number of connections that you can make through the reader endpoints in the proxy is 100 (50% of 200) for reader 1. It's also 100 for reader 2, and so on, for a total of 400. If you double the number of cluster reader DB instances to eight, then the maximum number of connections through the reader endpoints also doubles, to 800.

Additionally, I’d appreciate any insights on whether these limits apply per instance or if there's a different mechanism in place for managing connections through the RDS Proxy in a multi-instance environment.

As I read the explanation in the above document, I thought that it would be limited per instance rather than endpoint.

Furthermore, I am interested in setting different percentages for the connection pools of the Read-Write and Read-Only endpoints. Is creating two separate RDS Proxies the only way to achieve different connection pool percentages for these endpoints, or is there an alternative configuration within a single RDS Proxy setup?

Do you mean you want to set different percentages for writer and reader endpoints?
In that case, as far as I know, I don't think it can be configured with one RDS Proxy.