一般做负载均衡，都需要后端多台web服务器之间实现session共享，否则用户登录可能就有问题了。
今天看nginx文档时候，发现nginx可以根据客户端IP进行负载均衡，在upstream里设置ip_hash，就可以针对同一个C类地址段中的客户端选择同一个后端服务器，除非那个后端服务器宕了才会换一个。
原文如下：
The key for the hash is the class-C network address of the client. This method guarantees that the client request will always be forwarded to the same server. But if this server is considered inoperative, then the request of this client will be transferred to another server. This gives a high probability clients will always connect to the same server.
