Nginx快速定位异常
"upstream prematurely（过早的） closed connection"
请求uri的时候出现的异常，是由于upstream还未返回应答给用户时用户断掉连接造成的，对系统没有影响，可以忽略
"recv() failed (104: Connection reset by peer)"
（1）服务器的并发连接数超过了其承载量，服务器会将其中一些连接Down掉；
（2）客户关掉了浏览器，而服务器还在给客户端发送数据；
（3）浏览器端按了Stop
"(111: Connection refused) while connecting to upstream"
用户在连接时，若遇到后端upstream挂掉或者不通，会收到该错误
"(111: Connection refused) while reading response header from upstream"
用户在连接成功后读取数据时，若遇到后端upstream挂掉或者不通，会收到该错误
"(111: Connection refused) while sending request to upstream"
Nginx和upstream连接成功后发送数据时，若遇到后端upstream挂掉或者不通，会收到该错误
"(110: Connection timed out) while connecting to upstream"
nginx连接后面的upstream时超时
"(110: Connection timed out) while reading upstream"
nginx读取来自upstream的响应时超时
"(110: Connection timed out) while reading response header from upstream"
nginx读取来自upstream的响应头时超时
"(110: Connection timed out) while reading upstream"
nginx读取来自upstream的响应时超时
"(104: Connection reset by peer) while connecting to upstream"
upstream发送了RST，将连接重置
"upstream sent invalid header while reading response header from upstream"
upstream发送的响应头无效
"upstream sent no valid HTTP/1.0 header while reading response header from upstream"
upstream发送的响应头无效
"client intended to send too large body"
用于设置允许接受的客户端请求内容的最大值，默认值是1M，client发送的body超过了设置值
"reopening logs"
用户发送kill -USR1命令
"gracefully shutting down"
用户发送kill -WINCH命令
"no servers are inside upstream"
upstream下未配置server
"no live upstreams while connecting to upstream"
upstream下的server全都挂了
"SSL_do_handshake() failed"
SSL握手失败
"ngx_slab_alloc() failed: no memory in SSL session shared cache"
ssl_session_cache大小不够等原因造成
"could not add new SSL session to the session cache while SSL handshaking"
ssl_session_cache大小不够等原因造成