This might be the best explanation I have seen of the benefits and pitfalls of deploying pgbouncer ( or any connection pooler as they are all similar ). The only thing I would add is from a deployment perspective, you should run two layers of pgbouncer. One that runs on the same host as your application ( sidecar container in k8s ), and one global layer that all connections to your DB must pass through. Every large scale application generally gets to this kind of architecture for various reasons, and it helps to just start with it. Some people will argue that connection pooling at the application layer is good enough to replace the sidecar proxy, but from my experience management is simplified by having the pooling done via the sidecar.
My large scale application certainly didn't run the pooler on the host. I don't see any reason to do this except for not wanting to become familiar with postgres itself.
What about running PHP, Django, Node, or Ruby based applications ? They all do connection per request so the pooler on host gives you an immediate improvement to connection latency.
Even if you are using a language with a built in connection pooler like Go or Java being able to manage your connections external to your application is enough of a benefit to keep the pooler separate.
