Some other 'solutions' you can try;
https://www.scalescale.com/tips/nginx/upstream-timed-out/
http://serverfault.com/questions/647411/nginx-lots-of-connection-timed-out-errors
https://kb.plesk.com/en/120210
http://stackoverflow.com/questions/28347184/upstream-timed-out-110-connection-timed-out-for-static-content
https://www.scalescale.com/tips/nginx/upstream-timed-out/
http://serverfault.com/questions/647411/nginx-lots-of-connection-timed-out-errors
https://kb.plesk.com/en/120210
http://stackoverflow.com/questions/28347184/upstream-timed-out-110-connection-timed-out-for-static-content