protected void reusePooledConnection(
            CurrentPassport passport,
            AtomicReference<? super InetAddress> selectedHostAddr,
            PooledConnection conn,
            Promise<PooledConnection> promise) {
        conn.startRequestTimer();
        conn.incrementUsageCount();
        conn.getChannel().read();
        onAcquire(conn, passport);
        initPooledConnection(conn, promise);
        selectedHostAddr.set(getSelectedHostString(serverAddr));
    }
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