Hi Martin,
thank you. Definitely I want to propose patch to libvirt-guests, but this weekend I am taking family holiday, so be patient and wait little bit more.On Wed, Sep 23, 2015 at 3:12 PM, Martin Kletzander <mkletzan@xxxxxxxxxx> wrote:
Oh, so here is what I have misunderstood. Well, just misread, ofOn Wed, Sep 23, 2015 at 11:39:29AM +0200, Marek Lukács wrote:
Hi Martin,
thank you for your reply. Please check my comments.
On Wed, Sep 23, 2015 at 10:50 AM, Martin Kletzander <mkletzan@xxxxxxxxxx>
wrote:
On Tue, Sep 22, 2015 at 07:33:30AM +0200, Marek Lukács wrote:
Hi,To be honest, I don't think that's _exactly_ what you want _just_ from
It will be nice feature to have configuration option
ALWAYS_START="$uri:$name $uri:name ..." in libvirt-guests
configuration file.
If ON_BOOT is "start" and if ALWAYS_START is not empty, it iterates
over the ALWAYS_START and starts guests with same conditions (delays
etc.) before it starts guests from LISTFILE.
libvirt itself; let me explain.
Benefits:
- guests are started with delays
Delays that are done due to the guests are not something we should
handle. Guests and mainly the applications inside them should handle
this gracefully. Just delaying the starts is still error-prone.
I fully understand this and fully agree with you. Production application
has to handle this gracefully. But still I see a space for doing it in
environments where it is not so necessary to configure application so
gracefully, like development or testing environments. Delays are fine for
many not production environments, where applications are not in production
state.
- guests are started after host failure
That's what libvirt-guests does already. And if you want some domains
to be started on every start, there's the 'autostart' parameter for
domains.
No, libvirt-guests only starts those domains which has been running before
"service" libvirt-guests has been stopped. In case of host failure, there
is no LISTFILE in filesystem, as it has not been generated by
libvirt-guests stop mechanism.
course libvirt-guests doesn't handle host failures.
But probably I do not understand "script" libvirt-guests correctly and why
it is in libvirt. I will be happy, if you will give me more details, why
there is this script, even if libvirt has 'autostart' parameter for domains.
- For what usage is libvirt-guests designed?
My interpretation is that it is there in order for you to be able to
shutdown and boot later without losing the machines you were running.
Autostart says that particular domain should be started every time the
daemon is started. Basically says that particular guest should be
running on the host all the time.
- Why it supports delays?
Because most of the time you'll want to resume from managed save and
you might cause a big load in case you're starting bunch of machines
because all of those will start loading everything from disk and so
on.
- Why to have libvirt-guests if there is 'autostart' domain parameter?
It does two different things. Domain with autostart will be started
every time daemon (actually not even the computer) is started, but
libvirt-guests will stop/save domains that are running when the
computer is being shut down and start/resume them when it is starting
back.
- For who is libvirt-guests and who should use 'autostart' domain parameter?
Well, libvirt-guests was added by a guy who was too lazy to clean up
his machine before rebooting (sorry Jirka, I had to). But you get the
picture. Use it for whatever you like and whatever suits you. I'm
not even against adding what you suggested, I just wanted to make sure
you're not relying on the script for something critical as my
understanding of it that it is not very error prone.Well, there is no reference purpose and as I said I'm not even against
- guests are started in specific order (for example complex
environment, when DB should be started before other guest, etc.)Again, same as the first point. This should be handled gracefully in
the application itself or at least worked around in the guest (not
starting DB-related app before DB is accessible).
Anyway, if you *really* want this, then the easiest thing to do is
creating a service that starts before libvirt-guests, but after
libvirt, which is just something similar to "local", so it just runs a
script that does:
for i in domain_one some_other_domain database_dom
do
virsh start "$i"
sleep 60 # or you can try connecting to make sure it started
done
or something similar. However, you might still propose a simple patch
for the feature you described.
For me it is no problem to design my own script to handle my needs. I have
spent some time googling, if there is already a tool for it. I found only
similar questions, so I got feeling, that I am not the only one with
similar requirements.
Script libvirt-guests in my eyes handles very similar task. It starts
domains with delays, it starts domains what has been running at previous
stop, but do not handle situation in case of host failure and do not starts
domain in specific order. I prefer and I think, that it is better to not
create new script no one knows about, but to modify existing one everybody
knows about. But again, maybe I do not understand why and for what
libvirt-guests is.
adding your option there. And if we get it into libvirt-guests,
others might use it. Would you mind proposing it as a patch? It
could be pretty straightforward, I guess.
Have a nice day,
Martin
Anyway, much easier in case of testing and development environments is to
set start sequence in /etc/rc.local and forget about script like
libvirt-guests, if it does not have features I described.
Regards,
Marek Lukács
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