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From: Christos Trochalakis <yatiohi@ideopolis.gr>
To: Eric Wong <e@80x24.org>
Cc: Dmitry Smirnov <onlyjob@debian.org>,
	Hleb Valoshka <375gnu@gmail.com>,
	unicorn@packages.debian.org, unicorn-public@bogomips.org
Subject: Re: [DRE-maint] unicorn: native systemd service
Date: Tue, 30 Jun 2015 12:20:26 +0300	[thread overview]
Message-ID: <20150630092026.GB6022@luke.ws.skroutz.gr> (raw)
In-Reply-To: <20150627030501.GA24759@dcvr.yhbt.net>

On Sat, Jun 27, 2015 at 03:05:01AM +0000, Eric Wong wrote:
>Christos Trochalakis <yatiohi@ideopolis.gr> wrote:
>> On Thu, Jun 25, 2015 at 11:26:26PM +0000, Eric Wong wrote:
>> >With socket activation, you should just be able to kill unicorn using
>> >SIGQUIT (just master, or even all workers) and restart without ever
>> >dropping a connection.  I do NOT suggest using SIGTERM for unicorn,
>> >since that'll cause the master to kill all workers ASAP.
>> Yes, you are right socket activation is also an option! I have made some
>> experiments with a simple rack app to test it.
>> systemd uses the LISTEN_FDS env variable that is an integer indicating the
>> number of inherited file descriptors. Those FDs have consecutive numbers
>> starting from `SD_LISTEN_FDS_START` which is `3` (man sd_listen_fds).
>> So for example if LISTEN_FDS="2", UNICORN_FD should be "3,4". I used a
>> simple wrapper script for that. Here is the full configuration:
>OK, I'll probably add LISTEN_FDS and LISTEN_PID support to unicorn
>directly so the wrapper is unnecessary.
>> KillMode=mixed
>I don't think KillMode=mixed is necessary, here.  systemd can send
>SIGQUIT to workers.

Perhaps there is a race here, if a worker receives SIGQUIT first, and the
master respawns a new worker before receiving/handling its own SIGQUIT.
This is definitely a longshot, and will probably never happen, but
even then every process will eventually quit gracefully.

>> TCP socket options are not applied by unicorn on inherited sockets (TCPSocket
>> === sock is false). systemd socket files have support for most options now but
>> we might want unicorn to `setsockopt` them as well. For example,
>> 'DeferAcceptSec', 'KeepAliveIntervalSec', 'NoDelay' are supported since v216, so
>> they are not available in jessie (v215).
>They are now :)
>We don't have KeepAliveIntervalSec
>(aka TCP_KEEPINTVL) since it's not-portable and probably over
>Are you sure about that?

I added 'KeepAliveIntervalSec' by mistake. `KeepAlive`, a supported
option by unicorn, is included in jessie (systemd v215). Either way with
your last patch those options are enforced by unicorn.

>> socket activation is a really interesting setup, but personally I would not run
>> it with a large application. Clients would have to wait for the new master to
>> be up and running before a reply is returned, and that could take tenths of
>> seconds. The USR2 rexec solves that problem since both old and new workers are
>> accepting on the socket and we can kill the old ones when we are ready. In that
>> case the PIDFile trick is handy to support zero downtime restarts with no
>> latency.
>Is it possible to make systemd fire up two unicorn masters?
>That would be a nice feature to have with socket activation.

That would be great! I am a bit surprised that specifying multiple
services ('Service=' option) is not supported.

  parent reply	other threads:[~2015-06-30  9:20 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <16714105.fRFKlev1fp@debstor>
     [not found] ` <3137844.nsIDTWmvl4@debstor>
     [not found]   ` <CAAB-Kc=s-uSK83PcfDsybPRiYvTaLVxcu2x4eWDPaTf27AJ_XQ@mail.gmail.com>
     [not found]     ` <1810167.FXDESjsu8Z@debstor>
2015-06-24 23:26       ` unicorn: native systemd service Eric Wong
2015-06-25 23:43         ` Dmitry Smirnov
2015-06-25 23:49           ` Eric Wong
     [not found]   ` <20150625083118.GA22140@luke.ws.skroutz.gr>
2015-06-25 23:26     ` [DRE-maint] " Eric Wong
2015-06-26 11:41       ` Christos Trochalakis
2015-06-27  3:05         ` Eric Wong
2015-06-27  4:01           ` [RFC] emulate sd_listen_fds for systemd support Eric Wong
2015-06-30  8:47             ` Christos Trochalakis
2015-07-05  0:27               ` [PATCH v2] " Eric Wong
2015-06-30  9:20           ` Christos Trochalakis [this message]
2015-06-30 17:30             ` [DRE-maint] unicorn: native systemd service Eric Wong
2015-07-08 13:08               ` Christos Trochalakis

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