nginx 连接限制新语法

[SNIA Computer System] The ability of a system to perform its function continuously (without interruption) for a significantly longer period of time than the reliabilities of its individual components would suggest.系统在相当长的时间范围内连续不中断地执行其功能的能力，这个时间段要长于其独立组件所支持工作的时间。High availability is most often achieved through failure tolerance. High availability is not an easily quantifiable term. Both the bounds of a system that is called highly available and the degree to which its availability is extraordinary must be clearly understood on a case-by-case basis.获取高可用性最常用的方式是容错。高可用性不是一个容易计量的术语。必须在逐个基础项，同时清晰地理解要求具有高可用性的系统本身所具有的限制以及可用性所能达到的程度。 简单地说高可用性主要是指系统的稳定性和数据的可靠性。稳定性指作为服务方的中心主机能够提供持续不间断服务的能力即7×24小时的服务。可靠性是指系统出错情况下数据不会丢失出错。