upstream prematurely closed connection while reading response header from upstream nginx iis

nginx代理iis，外网突然报502
nginx日志upstream prematurely closed connection while reading response header from upstream
查看iis日志发现有收到请求，但是回调时候走了1.0，导致nginx没处理；
nginx增加proxy转换后解决：

proxy_http_version 1.1;
proxy_set_header Connection "";