code: public NettyServerBuilder permitKeepAliveTime(long keepAliveTime, TimeUnit timeUnit) {
      checkArgument(keepAliveTime >= 0, "permit keepalive time must be non-negative");
      permitKeepAliveTimeInNanos = timeUnit.toNanos(keepAliveTime);
      return this;
    }
docs: Specify the most aggressive keep-alive time clients are permitted to configure. The server will
  try to detect clients exceeding this rate and when detected will forcefully close the
  connection. The default is 5 minutes.
  
  <p>Even though a default is defined that allows some keep-alives, clients must not use
  keep-alive without approval from the service owner. Otherwise, they may experience failures in
  the future if the service becomes more restrictive. When unthrottled, keep-alives can cause a
  significant amount of traffic and CPU usage, so clients and servers should be conservative in
  what they use and accept.
  
  @see #permitKeepAliveWithoutCalls(boolean)
  @since 1.3.0