Does RDS proxy affects current application side pooling?

Question

I have a Saas application on AWS ECS and databases on AWS RDS. We are planning to implement AWS RDS Proxy for pooling implementation. From the RDS proxy documentation, I saw that we don't need to make any changes to the application code. Currently, we are using application side connection pooling. When we implement an RDS proxy for pooling, does the current pooling have any impact?

Do we need to remove the application side pooling to work with RDS effectively?

My main concern is, if I choose 100% pooling in RDS proxy and from application pooling configuration if we limit that to say 100 max connection. Will that be a bottleneck?

Answer 1

TLDR: keep the connection pool in your application, and size it to the number of connections required by that one instance of your application (e.g. the ECS task or EKS pod).

With a database proxy in the middle, there are two separate legs to a "connection":

1. First, there is a connection from the application to the proxy. What you called the "application side pooling" is this type of connection. Since there's still overhead associated with creating a new instance of this type of connection, continuing to use a connection pool in your application probably is a good idea.
2. Second, there is a connection from the proxy to the database. These connections are managed by the proxy. The number of connections of this type is controlled by a proxy configuration. If you set this configuration to 100%, then you're allowing the proxy to use up to the database's max_connections value, and other clients may be starved for connections.

So, when your application wants to use a connection, it needs to get a connection from its local pool. Then, the proxy needs to pair that with a connection to the database. The proxy will reuse connections to the database where possible (this technique also is called multiplexing). Or, quoting the official docs: "You can open many simultaneous connections to the proxy, and the proxy keeps a smaller number of connections open to the DB instance or cluster. Doing so further minimizes the memory overhead for connections on the database server. This technique also reduces the chance of "too many connections" errors."

As your container orchestrator (e.g. ECS or EKS) scales your application horizontally, your application will open/close connections to the proxy, but the proxy will prevent your database from becoming overwhelmed by these changes.