netdev - Re: Seamless Service Restart / Port Takeover

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Message-ID: <CAGVGHmugM7Ta3mafe1V5n76QZrZzCryMo3kr=XPfb4knmPP_hg@mail.gmail.com>
Date:	Thu, 13 Oct 2011 11:56:04 +0200
From:	Olaf van der Spek <ml@...pek.org>
To:	Rick Jones <rick.jones2@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: Seamless Service Restart / Port Takeover

On Wed, Oct 12, 2011 at 7:14 PM, Rick Jones <rick.jones2@...com> wrote:
> On 10/12/2011 09:53 AM, Olaf van der Spek wrote:
>>
>> Hi,
>>
>> When restarting a service, a webserver for example, you'd like this to
>> be seamless for clients. Often, first a signal is send to the old
>> process to close listening sockets, then the new process is started.
>> This has both a race condition (sometimes 'avoided' with a sleep in
>> between) and service interruption.
>> Wouldn't it be possible to introduce mv / move like behaviour, where
>> the socket can be rebound without races and without interruption?
>
> I believe you can do that today if you write the application such that the
> old instance, before it closes the listen endpoint and terminates, instead
> passes access to it to the new instance via a Unix domain socket between the
> two.

Hi Rick,

That sounds rather complicated. What daemons implement the
functionality this way?
I think an easier way to accomplish this would be quite welcome.

Olaf
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