We are using nodejs(v 0.10.29 ) ,express,nginx( version 1.4.6) with mongodb(v 2.6.3) replicaset and getting intermittent 502 bad gateway error. pm2 logs is unable to log error though nginx aerror.log is showing

recv() failed (104: Connection reset by peer) while reading response header from upstream, client: xxx.xxx.xxx.xxx, server: somedomain.com, request: "GET /img/abc.png HTTP/1.1", upstream: "http://127.0.0.1:3000/img/abc.png", host: "domain.com", referrer: "http://domain.com/admin/"

and access.log is saying:

"GET /url/abc.html HTTP/1.1" 502 723 "http://domain.com/admin/" "Mozilla/5.0 (X11; Linux i686) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Safari/537.36"

can anyone guide me with the issue?