nginx proxy_next_upstream模块 重复提交问题

proxy_next_upstream表示对于后端服务器，出现问题后将会转移到另外一台服务器

proxy_next_upstream

语法: proxy_next_upstream [error|timeout|invalid_header|http_500|http_503|http_404|off]

默认值: proxy_next_upstream error timeout

上下文: http, server, location

Directive determines, in what cases the request will be transmitted to the next server:

• error ― an error has occurred while connecting to the server, sending a request to it, or reading its response;
• timeout ― occurred timeout during the connection with the server, transfer the requst or while reading response from the server;
• invalid_header ― server returned a empty or incorrect answer;
• http_500 ― server returned answer with code 500
• http_503 ― server returned answer with code 503
• http_404 ― server returned answer with code 404
• off ― it forbids the request transfer to the next server

Transferring the request to the next server is only possible when nothing has been transferred to the client -- that is, if an error or timeout arises in the middle of the transfer of the request, then it is not possible to retry the current request on a different server.