Re: [lvs-users] ldirectord parallelising checks ?

To: " users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [lvs-users] ldirectord parallelising checks ?
From: chris barry <Christopher.Barry@xxxxxxxxxx>
Date: Thu, 20 Dec 2007 01:50:08 -0500
On Thu, 2007-12-20 at 14:18 +0900, Simon Horman wrote:
> On Wed, Dec 19, 2007 at 12:28:30PM -0600, Aaron Linnen wrote:
> > Jean-Paul BALOCHE [STG] wrote:
> > > Hi,
> > >
> > > I'm a new user of ldirectord. I've got a running configuration with 20 
> > > http servers.
> > > I've got a question regarding the way ldirector check the availibilty of 
> > > http servers.
> > > On each http server, I've got 10 virtual hosts each one on a specific 
> > > port. ldirector is configured to check every virtual host of every 
> > > servers. It do it sequentialy, so if several virtual hosts are done, I 
> > > have to wait for the timeout to arrive. So it take a long time to check 
> > > all servers. Is it possible to parallelise checks ?
> > >
> > > Thanks for your answer ;-)
> > >
> > > JPB
> > >   
> > You can look in the list archives for the thread titled RFC: Forking 
> > ldirecterd [PATCH] by Ryan Castellucci which starts with:
> > 
> >   The attached patch modifies ldirectord to fork a process for each
> >   virtual server to speed up response time with large numbers of virtual
> >   servers. I am testing this vs multiple instances of ldirectord, two
> >   virtual servers, three real servers each, and it uses about 25MB less
> >   ram over that, and starts up a lot quicker.
> > 
> > 
> > Looks like what you want. That patch should be included in the next 
> > ldirectord release.
> Its possible to parallelise the checks at the real-server level and
> at the virtual-service level. Currently ldirectord only supports the
> latter in two different ways, "execute" and "fork". 
> "execute" is an older way of having ldirectord run multiple processes.
> By adding one or more execute directives to an file
> it will spawn a copy of ldirectord with the specified sub-configuration
> file. By splitting virtual services up between configuration files,
> some degree of parallelism can be achieved.
> "fork" is a new method, which when activated in the configuration
> file causes ldirectord to spawn a child process for each virtual
> service. Again, this gives elms parallelism in the checks. This
> was added to the repository quite recently, and as Aaron mentions,
> should appear in the next release.
> Neither of these methods address parallisation at the real-server level.
> Forking is probably a bit heavy for this. But on the other hand,
> many of the protocol checks included in ldirectord can't readily
> be ported to a select()/poll()/whatever based method of having
> a single process handle multiple requests simultaneously. In sorts,
> its a somewhat more tricky problem than the parallelisation options
> that are already supported.
> Lastly, ldirectord does include some code such that if the same
> real-server is present in multible virtual-services (that will
> be checked by the same ldirectord process), then the check
> is only preformed once per loop, rather than once for each
> virtual-service that it appears in. If there are several
> virtual-services mapping onto the same group of real-servers
> this can be a big win.

To your last point, while this verifies the RS itself is responding to
'something', a ping perhaps, it does not verify the 'skipped' service on
the RS is up and returning expected results. Or am I misunderstanding


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