Coming from ActiveRecord gem, pgbouncer has been great. I'd say the real advantage is transaction level pooling, which will free up connections when they're not

Coming from ActiveRecord gem, pgbouncer has been great. I'd say the real advantage is transaction level pooling, which will free up connections when they're not actively in a transaction (vs request level isolation). I don't see how this is possible across a large number of isolated servers without a cooperating agent like pgbouncer. I would advocate for pgbouncer at the DB ingress level and your languages connection pooler at the application level.