protected boolean isConnectionExpired(long usageCount) {
        // if the connection has been around too long (i.e. too many requests), then close it
        // TODO(argha-c): Document what is a reasonable default here, and the class of origins that optimizes for
        return usageCount > connPoolConfig.getMaxRequestsPerConnection();
    }
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