nginx常见内部错误
错误日志：
| 错误信息 | 错误说明 |
| upstream prematurely closed connection(过早地关掉连接) |
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，服务器会将其中一部分连接Down掉； 2).客户端主动关闭连接，而服务器还正在给客户端发送数据； 3).浏览器端按了stop； |
| (111:Connection refused) while connection to upstream | 用户在连接时，若遇到后端upstream挂掉或者不通，会受到该错误 |
| (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upsteam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 time out) while connection to upstream | nginx连接后面的upstream时，超时 |
| (110:Connection time out) while reading upstream | nginx读取来自upstream的响应时，超时 |
| (110:Connection time out) while reading response header from upstream | nginx读取来自upstream的响应头时，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 to valid HTTP/1.0 header while reading response header from upstream | upstream发送的响应头无效 |
| client intended to send to large body | 用于设置允许接收的客户端请求内容的最大值，默认值是1M，client发送的body超过了设置的值 |
| 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下未设置server |
| no live upstream while connection to upstream | upstream下的server全都挂了 |
| SSL_do_handshake() failed. | SSL握手失败 |
| SSL_write() failed(SSL:) while sending to client | |
| (13:Permission denied) while reading upstream | |
| (98:Address already in use) while connection to upstream | |
| (99:Cannot assign requested address) while connection to upstream | |
| ngx_slag_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 handsharking | ssl_session_cache 大小不够等原因造成 |
| send() failed (111:Connection refused) | |
