protected void updateServerStatsOnRelease(PooledConnection conn) {
        DiscoveryResult discoveryResult = conn.getServer();
        discoveryResult.decrementActiveRequestsCount();
        discoveryResult.incrementNumRequests();
    }
Gracefully shuts down a DefaultClientChannelManager by allowing in-flight requests to finish before closing the connections.
Idle connections in the connection pools are closed, and any connections associated with an in-flight request
will be closed upon trying to return the connection to the pool
zuul-core/src/main/java/com/netflix/zuul/netty/connectionpool/DefaultClientChannelManager.java