Zero-Downtime Servicing of a Varnish Server Behind a F5 BIG-IP

[Hettwer, Marian]

Actually the F5 box would have the same problem as you're describing for
varnish.
If the F5 box behaves correctly, marking the varnish out of service means
that the F5 should not accept new connections, but is also not allowed to
drop existing connections.

Therefor I do wonder how the F5 machine would solve this without errors to
the client.
I would bet it also aggressively shuts down existing connections.

Or if it doesn't, well okay, then there is nearly no way around it for
doing it on the varnish.


You might think about installing two varnish boxes in an active/passive
carp(4) and pfsync(4) setup. But that means you probably have to go with
FreeBSD on your server. I'm not sure about implementations of carp(4) and
pfsync(4) for linux.


With carp you could do the fail over you wanna do.
While thinking about it, active/active carp(4) would work too.

So carp(4) / pfsync(4) for the win it is! :-D

HTH,
Marian

On 09.07.12 23:24, "Steven Engelhardt" <sengelha at gmail.com> wrote:

>Because of the usage patterns of the web service, I'm not sure that even
>a 1-second timeout would be sufficient to get all HTTP client connections
>to close.
>
>
>The idea of setting sess_timeout to be 0 was strictly in the context of
>taking a Varnish server out of service, in order to (somewhat indirectly)
>force the out of service Varnish server to close all its HTTP
>connections.  We would restore sess_timeout to a
> sensible value before putting it back in service.
>
>
>Steve
>
>On Mon, Jul 9, 2012 at 4:07 PM, Javier Casares
><javier at casares.org> wrote:
>
>If  sess_timeout  is set by default to 5 seconds, you could try to set
>this to 4, 3, 2 or 1 and test if has a better performance... i suposse
>that set this to 0 will close all connectiond and seems to be an epic
>fail...
>
>Javier Casares
>http://javiercasares.com/
>
>
>2012/7/9 Steven Engelhardt <sengelha at gmail.com>:
>> Just to be clear, would you suggest something like:
>> 1. Mark the Varnish server as disabled in the BIG-IP
>> 2. Use varnishadm to set sess_timeout to 0 to start aggressively closing
>> HTTP requests?
>> 3. Wait for connections to drain
>>
>> Steve
>>
>> On Mon, Jul 9, 2012 at 3:59 PM, Javier Casares <javier at casares.org>
>>wrote:
>>>
>>> 
>https://www.varnish-cache.org/docs/3.0/reference/varnishd.html
><https://www.varnish-cache.org/docs/3.0/reference/varnishd.html>
>>>
>>> sess_timeout
>>>
>>>         Units: seconds
>>>         Default: 5
>>>
>>>     Idle timeout for persistent sessions. If a HTTP request has not
>>> been received in this many seconds, the session is closed.
>>>
>>> ¿?
>>>
>>> Javier Casares
>>> http://javiercasares.com/
>>>
>>>
>>> 2012/7/9 Steven Engelhardt <sengelha at gmail.com>:
>>> > I have two Varnish servers behind a F5 BIG-IP load balancer.  Both
>>> > servers
>>> > are constantly active and serving ~5,000 requests/second 24x7.
>>>Clients
>>> > aggressively use HTTP 1.1 Keep-Alives.
>>> >
>>> > I'm looking to develop a process for servicing and upgrading the
>>>Varnish
>>> > servers which results in 0 downtime to the client.  Our normal
>>>process
>>> > for
>>> > performing changes on production servers is:
>>> > 1. Mark the server as disabled in the BIG-IP
>>> > 2. Wait for the connections on the server to drop to 0
>>> > 3. Service the machine
>>> >
>>> > However, because of the aggressive and constant use of HTTP
>>>Keep-Alives,
>>> > clients virtually never drop their connections, and the machine
>>> > continues to
>>> > serve traffic for quite a long time after it is disabled in the
>>>BIG-IP.
>>> >
>>> > Is there a way to tell Varnish to aggressively close all client HTTP
>>> > connections?
>>> >
>>> > Thank you,
>>> > Steve
>>> >
>>> > --
>>> > Steven Engelhardt
>>> > sengelha at gmail.com
>>> >
>>> > _______________________________________________
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>>> > varnish-misc at varnish-cache.org
>>> > 
>https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc
><https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc>
>>>
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>>
>>
>>
>>
>> --
>> Steven Engelhardt
>> sengelha at gmail.com
>>
>> _______________________________________________
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>> varnish-misc at varnish-cache.org
>> 
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><https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc>
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>
>
>
>
>
>
>-- 
>Steven Engelhardt
>sengelha at gmail.com
>