Re: [Xen-users] how to start VMs in a particular order

[Joost Roeleveld <joost@xxxxxxxxxxxx>]

On Sunday 29 June 2014 18:31:44 lee wrote:
> "squidmobile@xxxxxxxxxxx" <squidmobile@xxxxxxxxxxx> writes:
> > granted, the lack of dns affects the nfs clients, but wouldn't the
> > nfs server (mostly) ignore dns until it finished booting and began
> > nfs operations?
> 
> No --- or maybe.  When you put host names into exports, the NFS server
> tries to resolve them.  IIRC it does that when reading exports, which it
> has to before others can require its services (which one of the other
> VMs does).

Also my experience.

> >> How do you find out whether a VM is fully up or not even within the very
> >> same VM?
> > 
> > well, dom0 can maintain a log of vm console output (i forget
> > exactly where, but i think somewhere under /var/log/xen/console).
> > tweak your vm startup scripts to echo something like "start the
> > next vm" and let the dom0 auto script wait for the signal before xl
> > create the next vm.  put a sleep 5 in the auto script to keep it
> > from thrashing.  would some variant of this work for you?
> 
> I think enforcing a particular order in which the VMs are started and a
> waiting period between starting each VM is the most reasonable approach
> in my case.
> 
> It has the advantage of not needing to modify each VM to send a "ready"
> message and not needing to somehow catch all the console output of each
> VM.  That keeps things a lot simpler and less prone to mistakes and
> errors.

I used to do it this way. Untill I ended up with varying boot times due to 
aging hardware, network congestion to the internet for some services and 
filesystem checks because of max mount-count reached or too long without 
checking.
With the disks you are using, you are more likely to end up with varying boot 
times then if you would be using disks that do not have aggressive 
powersaving.

> The disadvantage is that it might take a bit longer than otherwise until
> all VMs are up.  IMO, the simplicity outweighs the disadvantage,
> especially since I can adjust the timers to minimise the waiting
> periods.
> 
> I guess I could "encode" the waiting periods in the file names ... With
> a name like '02-0300-VMx.cfg', I could make the starting script wait 300
> seconds before it actually starts that VM, and it would start
> '01-0000-VMz.cfg' before that, without waiting.  That would be plain and
> simple.
> 
> Actually, the default xendomains script should do that ...

No, it shouldn't.
An additional option inside the config-file might be an option. But I wouldn't 
want the default init-script to use the filename for any configuration item.

--
Joost

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