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

["J. Roeleveld" <joost@xxxxxxxxxxxx>]

On Saturday, June 28, 2014 01:11:05 PM lee wrote:
> "J. Roeleveld" <joost@xxxxxxxxxxxx> writes:
> > On Saturday, June 28, 2014 08:25:11 AM lee wrote:
> >> "J. Roeleveld" <joost@xxxxxxxxxxxx> writes:
> >> > On Thursday, June 26, 2014 06:19:30 PM lee wrote:
> >> >> Since dom0 crashes once every 24 hours, it would be nice if I could at
> >> >> least get the machine rebooted without more intervention than having
> >> >> to
> >> >> press the reset button ...
> >> > 
> >> > I would fix this with a higher priority, to be honest.
> >> 
> >> Yes, if I could ...
> >> 
> >> So far, I might have made some progress on that by removing a package
> >> that checks the status of the RAID volumes.  It's too early to tell for
> >> sure; at least the server hasn't crashed since.
> > 
> > Interesting. Maybe check on a Debian mailing list to see what that package
> > might be doing to cause a crash?
> 
> Apparently it's using arcconf to query the status of the
> volumes/controller.  Last crash, I got a message on the console saying
> that arcconf appeared to be hanging for 120 seconds, and the regularity
> of the crashes was suspicious.  The software is ancient, so it's
> possible that it causes problems with somewhat recent kernels :(

Quite possibly. Am I correct in assuming you are using old hardware with 
closed-source software?

> >> On Debian, /etc/init.d/xendomains seems to be what brings up the domains
> >> automatically.  It would be a good place to add a timer or to add checks
> >> for services.
> > 
> > That script is part of Xen, not just Debian. I have the same file in
> > Gentoo.
> Hm, is it still there when systemd is used?

When using systemd, it is not used.
However, I see more issues with using systemd instead of openrc when compared 
to the benefits.
I use Xen on servers where stability is more important then a fast boottime. 
(especially as the BIOS takes longer then booting the OS)

> >> So when you're careful, you can specify the order in which VMs are
> >> brought up (at least when using Debians' script) --- but is it a granted
> >> feature that the names always appear in any particular order?  It looks
> >> more like a side effect.
> > 
> > It is how the shell, by default, orders files when enumerating wild-cards.
> > This can be relied upon.
> 
> With any shell that might be used?

I use Bash or Perl when scripting. On both of these, I always have this 
behaviour.
It is also how classical sysv-init ensures the init-scripts are started in a 
consistent order. (used to be soft-links to the actual files using numbers at 
the start of the names.)

> >> Anyway, I think I'll modify the script so that the domains are brought
> >> up in a particular order with fixed delays as needed.  That seems the
> >> most simple and efficient way to do it.
> > 
> > I did something similar.
> > I have the following directories:
> > 
> > ****
> > # ls /etc/xen/auto/
> > disabled  stage1  stage2  stage3  stage4  stage5
> > ****
> > 
> > I then have duplicates for the xendomains script, with a few changes, that
> > starts the domains in the relevant stage folder.
> > Currently, I check that the domains in the stage-folder are started
> > successfully before the next one is started.
> 
> That's a good idea; I'll do that likewise.

All the domUs have their console inside a screen-session. These also log the 
output to:
/var/log/xen-consoles/<domu-name>.log

By checking if these have the login prompt, you can also ensure the domU has 
started correctly. At least the scripts I get with Gentoo cycle when the 
screen-session is created.

--
Joost

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