Re: [libvirt] [libvirt-guests] New feature ALWAYS_START
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. Regards, Marek On Wed, Sep 23, 2015 at 3:12 PM, Martin Kletzander <mklet...@redhat.com> wrote: > On 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 <mklet...@redhat.com> >> wrote: >> >> On Tue, Sep 22, 2015 at 07:33:30AM +0200, Marek Lukács wrote: >>> >>> Hi, >>>> >>>> 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. >>>> >>>> >>>> To be honest, I don't think that's _exactly_ what you want _just_ from >>> 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. >> >> > Oh, so here is what I have misunderstood. Well, just misread, of > 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. > > > >> - guests are started in specific order (for example complex >>> >>>> environment, when DB should be started before other guest, etc.) >>>> >>>> >&g
Re: [libvirt] [libvirt-guests] New feature ALWAYS_START
Hi Martin, thank you for your reply. Please check my comments. On Wed, Sep 23, 2015 at 10:50 AM, Martin Kletzander <mklet...@redhat.com> wrote: > On Tue, Sep 22, 2015 at 07:33:30AM +0200, Marek Lukács wrote: > >> Hi, >> >> 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. >> >> > To be honest, I don't think that's _exactly_ what you want _just_ from > 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. 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? - Why it supports delays? - Why to have libvirt-guests if there is 'autostart' domain parameter? - For who is libvirt-guests and who should use 'autostart' domain parameter? > - 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. 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 >> >> -- >> libvir-list mailing list >> libvir-list@redhat.com >> https://www.redhat.com/mailman/listinfo/libvir-list >> > -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
[libvirt] [libvirt-guests] New feature ALWAYS_START
Hi, 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. Benefits: - guests are started with delays - guests are started after host failure - guests are started in specific order (for example complex environment, when DB should be started before other guest, etc.) Regards, Marek Lukács -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
