+1 to ProxySQL, especially in RDS environments with huge monoliths attached that open a shitload of threads. RDS has fixed max_connections depending on the instance size so if you don't want to pay $$$$ for bigger but underused instances - and while you are trying to get the devs update all the hundreds old dependencies in the monolith to improve it, ProxySQL - can save your day. It did, for me. And yes, it's a self-managed system but it's pretty easy to operate and very stable.