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From: Pierre <oct@fotopedia.com>
To: unicorn list <mongrel-unicorn@rubyforge.org>
Subject: Re: Unicorn and HAProxy, 500 Internal errors after checks
Date: Thu, 2 Dec 2010 09:38:38 +0100	[thread overview]
Message-ID: <AANLkTimHCSGv9c-a9y+zN42_Gf+csTHQ+e5wh8OvKib9@mail.gmail.com> (raw)
In-Reply-To: <20101201195858.GD12001@dcvr.yhbt.net>


On Wed, Dec 1, 2010 at 8:58 PM, Eric Wong <normalperson@yhbt.net> wrote:
> Pierre <oct@fotopedia.com> wrote:
>> On Wed, Dec 1, 2010 at 5:52 PM, Eric Wong <normalperson@yhbt.net> wrote:
>> > Hi Pierre, HAProxy should be configured to send proper HTTP checks and
>> > not just TCP connection checks, the problem will go away then.
>> I understood this could be fixed this way and we will probably do that
>> soon. However, I think this is also the responsibility of Unicorn not
>> to reply anything when there's no request or at least log the error
>> somewhere :)
> I'm not sure how Unicorn is actually replying to anything, does HAProxy
> write *anything* to the socket?

It does. To reproduce the behavior, start a unicorn, start a sniffing
tool (ngrep for example), connect to the unicorn and disconnect

Connecting endpoint:

[08:22][virtual] root@infrabox:~# telnet localhost 2002
Connected to infrabox.virtual.ftnz.net.
Escape character is '^]'.
telnet> quit
Connection closed.

Sniffing Console:

[08:22][virtual] root@infrabox:~# ngrep "" port 2002 -d lo
interface: lo (
filter: (ip or ip6) and ( port 2002 )
T -> [AFP]
  HTTP/1.1 500 Internal Server Error....

Further packet inspection reveals that the 500 Internal Server Error
is sent after the telnet has sent a FIN packet which means it will
just be discarded. I understand logging it could be a DoS vector, but
you must admit that seing 500's from the server without any obvious
reason can be frightening at first.

Re HAProxy, and to complete Laurence reply from my point of view,

> If you serve large responses that can't fit in kernel socket buffers,
> then Unicorn will get stuck writing out to a client that isn't reading
> fast enough.

That can definitely be a problem in that case. To work around that we
use a cache in the stack above the lower level of HAProxy (we have two
other levels of HAProxy in the stack).

Pierre <oct@fotopedia.com>
Server Shepherd at http://www.fotopedia.com/
Unicorn mailing list - mongrel-unicorn@rubyforge.org
Do not quote signatures (like this one) or top post when replying

  parent reply	other threads:[~2010-12-02  9:05 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-12-01 11:59 Unicorn and HAProxy, 500 Internal errors after checks Pierre
2010-12-01 16:12 ` Clifton King
2010-12-01 17:02   ` Pierre
2010-12-01 16:52 ` Eric Wong
2010-12-01 17:14   ` Pierre
2010-12-01 19:58     ` Eric Wong
2010-12-02  0:42       ` Lawrence Pit
2010-12-02  4:59         ` Eric Wong
2010-12-02  8:38       ` Pierre [this message]
2010-12-02 17:39         ` Eric Wong
2010-12-03  8:41           ` Pierre
2010-12-04 23:38             ` Eric Wong
2010-12-05  1:04               ` russell muetzelfeldt
2010-12-06 18:39                 ` Eric Wong
2010-12-02 17:41     ` Eric Wong

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