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Re: how does LVS persistence work?

To: Tomasz Chmielewski <mangoo@xxxxxxxx>
Subject: Re: how does LVS persistence work?
Cc: lvs-devel@xxxxxxxxxxxxxxx
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Wed, 19 Oct 2011 06:40:37 +0900
On Tue, Oct 18, 2011 at 11:26:43PM +0200, Tomasz Chmielewski wrote:
> According to http://www.linuxvirtualserver.org/docs/persistence.html:
> 
>       In the persistent port, when a client first accesses the
>       service, LinuxDirector will create a connection template
>       between the given client and the selected server, then create
>       an entry for the connection in the hash table. The template
>       expires in a configurable time, and the template won't expire
>       until all its connections expire.
> 
> 
> Suppose I have two real servers and persistence set to 30 minutes.
> 
> 
> How will LVS persistence behave for a client which first connects at 01:00?
> 
> 1) persistence is always "first connected + 30 minutes".
> 
> When the client connects at 01:00, LVS sets persistence to 30 minutes.
> All connections from this client, between 01:00-01:30 will be
> directed to one server.
> At ~01:31, persistence will expire and will be set again; it's
> possible that the client will hit the other server, even though the
> last connection was made at 01:29.
> 
> Meaning - if the client makes one short connection every 25 minutes
> and persistence is set to 30 minutes, the chances are it will hit a
> different server (almost) every time.
> 
> lvs-devel@xxxxxxxxxxxxxxx
> 2) persistence is always extended and is "last connection + 30 minutes".
> 
> In other words - if the client makes one short connection every 25
> minutes and persistence is set to 30 minutes, it is practically
> guaranteed the client will always hit the same server.
> 
> 
> Which one is true, 1) or 2)?

2) is true.
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