getting intermittent '502 bad gateway ' error.

[shobhit]

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?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,252227,252227#msg-252227