protected boolean isOverPerServerWaterline(int connectionsInPool) {
        int poolWaterline = config.perServerWaterline();
        return poolWaterline > -1 && connectionsInPool >= poolWaterline;
    }
function to run when a connection is acquired before returning it to caller.
zuul-core/src/main/java/com/netflix/zuul/netty/connectionpool/PerServerConnectionPool.java