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I have a machine running Haproxy. Under heavy load, I can see that all the response codes are 503. The back end server for a lot of the entries in the log file is NOSRV, but not all:

https_proxy https_proxy/NOSRV -1/1/2/-1/1034 503
https_proxy https_proxy/MYSERVER3 -1/1/0/-1/562 503

(removed angle brackets around NOSRV above as wasn't displaying properly with them)

MYSERVER3 has a lot of connections in CLOSE_WAIT. I'm not sure how to approach the problem - perhaps forceclose in Haproxy, increase kernel parameter net.core.somaxconn on the Haproxy box, something else?

Any guidance greatly appreciated.

Thanks, Paul

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I would sincerely doubt HAProxy is your issue. Even with a default configuration file, it can handle tens of thousands of requests per second.

Your issues are more likely to be the back end that it is passing requests to.

Have a look at this question, Tuning Linux + HAProxy

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