502, 575 errors appear in the access log

118.89.60.119 - - [01/May/2017:11:25:55 +0800] "GET /api/articles?
payload%5Bvalue%5D=&payload%5Badd%5D=true&payload%5Bpage%5D=4 HTTP/1.0" 502 
575 "http://www.xuhaodong.cn/articles" "Mozilla/5.0 (Windows NT 10.0; Win64; 
x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 
Safari/537.36" "-"

Error log

2017/05/01 11:24:33 [error] 28978#0: *64838 recv() failed (104: Connection 
reset by peer) while reading response header from upstream, client: 
118.89.60.119, server: www.xuhaodong.cn, request: "GET /api/articles?
payload%5Bvalue%5D=&payload%5Badd%5D=true&payload%5Bpage%5D=4 HTTP/1.0", 
upstream: "http://118.89.60.119:80/api/articles?
payload%5Bvalue%5D=&payload%5Badd%5D=true&payload%5Bpage%5D=4", host: 
"www.xuhaodong.cn", referrer: "http://www.xuhaodong.cn/articles"