On Sat, Jun 27, 2015 at 03:05:01AM +0000, Eric Wong wrote:
Christos Trochalakis <yati...@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.
<snip>
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.
<snip>
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 :)
http://bogomips.org/unicorn-public/m/1435373879-4299-1-git-send-emai...@80x24.org.txt
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.
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