A barrage of unexplained timeouts

Eric Wong normalperson at yhbt.net
Thu Aug 22 04:09:03 UTC 2013

Jimmy Soho <jimmy.soho at gmail.com> wrote:
> fwiw, we experience this too irregularly, about once a week or 2 weeks
> for a few seconds, and sometimes up to a minute or 2 minutes long. for
> no apparent reasons indeed. and at random times.

Wait, based on what you say below, is this happening to unicorn or

> my suspicion so far has always been that this is due to bad (wifi)
> networks of clients. what happens when a request is handled
> successfully by rails, but for whatever reason the last bit of the
> response can't be delivered because the receiving end is not consuming
> in a timely fashion?

So nginx is complaining about disconnected clients, not unicorn,

> If i'm not mistaken i think that rails logs a 200 success message
> before the response is actually send back?

Correct, rails/unicorn won't know if the client disconnected until
nginx breaks the connection to unicorn.

> Is a response send back by rails / unicorn fully buffered by nginx? Or
> is a unicorn worker blocked until the response is confirmed to have
> been successfully received by the client?

nginx fully buffers both requests and responses by default.
Which leads us to...

> Aside: how do you protect your unicorn workers against a barrage of
> client requests that eat the response veeeeeery sloooooooowly?

That's the whole point of using nginx with unicorn.  nginx shields
unicorn from slow clients.

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