Re: [ovirt-users] Automatically migrate VM between hosts in the same cluster

18 Sep 2015

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On 18/09/15 07:30, Luca Bertoncello wrote:
...
Hi all,
thank you very much for your answers.
So:
1)Of course, we have UPS. More than one, in our server room, and of 
course they will send an advice to the host if they are on battery
Good.
...
2)My question was: what can I do, so that in case of Kernel Panic or 
similar, the VM will be migrated (live or not) to another host?
You would make the VMs HA and acquire a fencing solution.
...
3)Id like to have a shutdown-script on the host that put the host in 
Maintenance and wait until its done, so that I can just shutdown or 
reboot it without any other action. Is it possible? It would help to 
manage the power failure, too, assuming that other hosts have better 
UPS (it can be possible)
You could probably use the REST API on the Ovirt Engine for that.But it 
might be better to have a highly available machine (VM or not) running 
something like Nagios or Icinga which would perform the monitoring of 
your hosts and connect to the REST API to perform maintenance and 
shutdown. You might also consider a UPS service like NUT (unless you're 
already doing it).

Cheers

Alex
...
Thanks a lot
Mit freundlichen Grüßen
Luca Bertoncello
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*From:*users-bounces@ovirt.org [mailto:users-bounces@ovirt.org] *On 
Behalf Of *matthew lagoe
*Sent:* Thursday, September 17, 2015 9:56 PM
*To:* 'Alex Crow'; 'Yaniv Kaul'
*Cc:* users@ovirt.org
*Subject:* Re: [ovirt-users] Automatically migrate VM between hosts in 
the same cluster
There are PDUs that you can monitor power draw per port and that 
would kind of tell you if a PSU failed as the load would be 0
*From:*users-bounces@ovirt.org <mailto:users-bounces@ovirt.org> 
[mailto:users-bounces@ovirt.org] *On Behalf Of *Alex Crow
*Sent:* Thursday, September 17, 2015 12:31 PM
*To:* Yaniv Kaul <ykaul@redhat.com <mailto:ykaul@redhat.com>>
*Cc:* users@ovirt.org <mailto:users@ovirt.org>
*Subject:* Re: [ovirt-users] Automatically migrate VM between hosts in 
the same cluster
I don't really think this is practical:
- If the PSU failed, your UPS could alert you. If you have one...
If you have only one PSU in a host, a UPS is not going to stop you 
losing all the VMs on that host. OK, if you had N+1 PSUs, you may be 
able to monitor for this (IPMI/LOM/DRAC etc)and use the API to put a 
host into maintenance. Also a lot of people rely on low-cost white-box 
servers and decide that it's OK if a single PSU in a host dies, as, 
well, we have HA to start on other hosts. If they have N+1 PSUs in the 
hosts do they really have to migrate everything off? Swings and 
roundabouts really.
I'm also not sure I've seen any practical DC setups where a UPS can 
monitor the load for every single attached physical machine and figure 
out that one of the redundant PSUs in it has failed - I'd love to know 
if there are as that would be really cool.
- If the machine is going down in an ordinary flow, surely it can
    be done.
Isn't that what "Maintenance mode" is for?
Â
Even if it was a network failure and the host was still up,
        how would you live migrate a VM from a host you can't even
        talk to?
It could be suspended to disk (local) - if the disk is available.
Then the decision if it is to be resumed from local disk or not
    (as it might be HA'ed and is running elsewhere) need to be taken
    later, of course.
Yes, but that's not even remotely possible with Ovirt right now. I was 
trying to be practical as the OP has only just started using Ovirt and 
I think it might be a bit much to ask him to start coding up what he'd 
like.
Â
The only way you could do it was if you somehow magically knew
        far enough in advance that the host was about to fail (!) and
        that gave enough time to migrate the machines off. But how
        would you ever know that "machine quux.bar.net
        <http://quux.bar.net> is going to fail in 7 minutes"?
I completely agree there are situations in which you can't foresee
    the failure.Â
But in many, you can. In those cases, it makes sense for the host
    to self-initiate 'move to maintenance' mode. The policy of what to
    do when 'self-moving-to-maintenance-mode' could be pre-fetched
    from the engine.
Y.
Hmm, I would love that to be true. But I've seen so many so called 
"corner-cases" that I now think the failure area in a datacenter is a 
fractal with infinite corners. Yes, you could monitor SMART on local 
drives, pick up uncorrected ECC errors, use "sensors" to check for 
sagging voltages or high temps, but I don't think you can ever hope to 
catch everything, and you could end up doing a migration "storm" for . 
I've had more than enough of "Enterprise Spec" switches suddenly going 
nuts and spamming corrupt MACs all over the LAN to know you can't ever 
account for everything.
I think it's better to adopt the model of redundancy in software and 
services, so no-one even notices if a VM host goes away, there's 
always something else to take up the slack. Just like the origins of 
the Internet - the network should be dumb and the applications should 
cope with it! Any infrastructure that can't cope with the loss of a 
few VMs for a few minutes probably needs a refresh.
Cheers
Alex
.
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    <div class="moz-cite-prefix">On 18/09/15 07:30, Luca Bertoncello
      wrote:<br>
    </div>
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      <div class="WordSection1">
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi
            all,<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US">thank you very much for your answers.<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US">So:<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US"><o:p> </o:p></span></p>
        <p class="MsoListParagraph"
          style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US"><span style="mso-list:Ignore">1)<span
                style="font:7.0pt "Times New Roman"">      </span></span></span><!--[endif]--><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US">Of course, we have UPS. More than one, in our
            server room, and of course they will send an advice to the
            host if they are on battery</span></p>
      </div>
    </blockquote>
    <br>
    Good.<br>
    <br>
    <blockquote
      cite="mid:DC8168E813106D47ADB2BA2C8A46E9FF327AB9C13C@sphinx.queo.local"
      type="cite">
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        <p class="MsoListParagraph"
          style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US"><o:p></o:p></span></p>
        <p class="MsoListParagraph"
          style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US"><span style="mso-list:Ignore">2)<span
                style="font:7.0pt "Times New Roman"">      </span></span></span><!--[endif]--><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US">My question was: what can I do, so that in
            case of Kernel Panic or similar, the VM will be migrated
            (live or not) to another host?</span></p>
      </div>
    </blockquote>
    <br>
    You would make the VMs HA and acquire a fencing solution.<br>
    <br>
    <blockquote
      cite="mid:DC8168E813106D47ADB2BA2C8A46E9FF327AB9C13C@sphinx.queo.local"
      type="cite">
      <div class="WordSection1">
        <p class="MsoListParagraph"
          style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US"><o:p></o:p></span></p>
        <p class="MsoListParagraph"
          style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US"><span style="mso-list:Ignore">3)<span
                style="font:7.0pt "Times New Roman"">      </span></span></span><!--[endif]--><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US">Id like to have a shutdown-script on the host
            that put the host in Maintenance and wait until its done,
            so that I can just shutdown or reboot it without any other
            action. Is it possible? It would help to manage the power
            failure, too, assuming that other hosts have better UPS (it
            can be possible)</span></p>
      </div>
    </blockquote>
    <br>
    You could probably use the REST API on the Ovirt Engine for that.But
    it might be better to have a highly available machine (VM or not)
    running something like Nagios or Icinga which would perform the
    monitoring of your hosts and connect to the REST API to perform
    maintenance and shutdown. You might also consider a UPS service like
    NUT (unless you're already doing it).<br>
    <br>
    Cheers<br>
    <br>
    Alex<br>
    <br>
    <blockquote
      cite="mid:DC8168E813106D47ADB2BA2C8A46E9FF327AB9C13C@sphinx.queo.local"
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        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
            lang="EN-US">Thanks a lot<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
        <p class="MsoNormal" style="margin-bottom:12.0pt"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Mit
            freundlichen Grüßen<br>
            <br>
            Luca Bertoncello<br>
            <br>
            -- <br>
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              <p class="MsoNormal"><b><span
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style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
                  <a class="moz-txt-link-abbreviated" href="mailto:users-bounces@ovirt.org">users-bounces@ovirt.org</a>
                  [<a class="moz-txt-link-freetext" href="mailto:users-bounces@ovirt.org">mailto:users-bounces@ovirt.org</a>] <b>On Behalf Of </b>matthew
                  lagoe<br>
                  <b>Sent:</b> Thursday, September 17, 2015 9:56 PM<br>
                  <b>To:</b> 'Alex Crow'; 'Yaniv Kaul'<br>
                  <b>Cc:</b> <a class="moz-txt-link-abbreviated" href="mailto:users@ovirt.org">users@ovirt.org</a><br>
                  <b>Subject:</b> Re: [ovirt-users] Automatically
                  migrate VM between hosts in the same cluster<o:p></o:p></span></p>
            </div>
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          <p class="MsoNormal"><o:p> </o:p></p>
          <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
              lang="EN-US">There are PDUs that you can monitor power
              draw per port and that would kind of tell you if a PSU
              failed as the load would be 0<o:p></o:p></span></p>
          <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"
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          <div>
            <div style="border:none;border-top:solid #E1E1E1
              1.0pt;padding:3.0pt 0cm 0cm 0cm">
              <p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:windowtext"
                    lang="EN-US">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:windowtext"
                  lang="EN-US"> <a moz-do-not-send="true"
                    href="mailto:users-bounces@ovirt.org">users-bounces@ovirt.org</a>
                  [<a moz-do-not-send="true"
                    href="mailto:users-bounces@ovirt.org">mailto:users-bounces@ovirt.org</a>]
                  <b>On Behalf Of </b>Alex Crow<br>
                  <b>Sent:</b> Thursday, September 17, 2015 12:31 PM<br>
                  <b>To:</b> Yaniv Kaul <<a moz-do-not-send="true"
                    href="mailto:ykaul@redhat.com">ykaul@redhat.com</a>><br>
                  <b>Cc:</b> <a moz-do-not-send="true"
                    href="mailto:users@ovirt.org">users@ovirt.org</a><br>
                  <b>Subject:</b> Re: [ovirt-users] Automatically
                  migrate VM between hosts in the same cluster<o:p></o:p></span></p>
            </div>
          </div>
          <p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
          <p class="MsoNormal" style="margin-bottom:12.0pt"><span
              lang="EN-US">I don't really think this is practical:<br>
              <br>
              <o:p></o:p></span></p>
          <blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
            <div>
              <div>
                <div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">- If the PSU
                        failed, your UPS could alert you. If you have
                        one...<o:p></o:p></span></p>
                  </div>
                </div>
              </div>
            </div>
          </blockquote>
          <p class="MsoNormal" style="margin-bottom:12.0pt"><span
              lang="EN-US"><br>
              If you have only one PSU in a host, a UPS is not going to
              stop you losing all the VMs on that host. OK, if you had
              N+1 PSUs, you may be able to monitor for this
              (IPMI/LOM/DRAC etc)and use the API to put a host into
              maintenance. Also a lot of people rely on low-cost
              white-box servers and decide that it's OK if a single PSU
              in a host dies, as, well, we have HA to start on other
              hosts. If they have N+1 PSUs in the hosts do they really
              have to migrate everything off? Swings and roundabouts
              really.<br>
              <br>
              I'm also not sure I've seen any practical DC setups where
              a UPS can monitor the load for every single attached
              physical machine and figure out that one of the redundant
              PSUs in it has failed - I'd love to know if there are as
              that would be really cool.<br>
              <br>
              <o:p></o:p></span></p>
          <blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
            <div>
              <div>
                <div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">- If the
                        machine is going down in an ordinary flow,
                        surely it can be done. <o:p></o:p></span></p>
                  </div>
                </div>
              </div>
            </div>
          </blockquote>
          <p class="MsoNormal" style="margin-bottom:12.0pt"><span
              lang="EN-US"><br>
              Isn't that what "Maintenance mode" is for?<br>
              <br>
              <o:p></o:p></span></p>
          <blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
            <div>
              <div>
                <div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">Â <o:p></o:p></span></p>
                  </div>
                  <blockquote style="border:none;border-left:solid
                    #CCCCCC 1.0pt;padding:0cm 0cm 0cm
6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
                    <p class="MsoNormal"><span lang="EN-US"><br>
                        Even if it was a network failure and the host
                        was still up, how would you live migrate a VM
                        from a host you can't even talk to?<o:p></o:p></span></p>
                  </blockquote>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">It could be
                        suspended to disk (local) - if the disk is
                        available.<o:p></o:p></span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">Then the
                        decision if it is to be resumed from local disk
                        or not (as it might be HA'ed and is running
                        elsewhere) need to be taken later, of course.<o:p></o:p></span></p>
                  </div>
                </div>
              </div>
            </div>
          </blockquote>
          <p class="MsoNormal" style="margin-bottom:12.0pt"><span
              lang="EN-US"><br>
              Yes, but that's not even remotely possible with Ovirt
              right now. I was trying to be practical as the OP has only
              just started using Ovirt and I think it might be a bit
              much to ask him to start coding up what he'd like.<br>
              <br>
              <o:p></o:p></span></p>
          <blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
            <div>
              <div>
                <div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">Â <o:p></o:p></span></p>
                  </div>
                  <blockquote style="border:none;border-left:solid
                    #CCCCCC 1.0pt;padding:0cm 0cm 0cm
6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
                    <p class="MsoNormal"><span lang="EN-US"><br>
                        The only way you could do it was if you somehow
                        magically knew far enough in advance that the
                        host was about to fail (!) and that gave enough
                        time to migrate the machines off. But how would
                        you ever know that "machine <a
                          moz-do-not-send="true"
                          href="http://quux.bar.net" target="_blank">quux.bar.net</a>
                        is going to fail in 7 minutes"?<o:p></o:p></span></p>
                  </blockquote>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">I completely
                        agree there are situations in which you can't
                        foresee the failure.Â <o:p></o:p></span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">But in many,
                        you can. In those cases, it makes sense for the
                        host to self-initiate 'move to maintenance'
                        mode. The policy of what to do when
                        'self-moving-to-maintenance-mode' could be
                        pre-fetched from the engine.<o:p></o:p></span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><span lang="EN-US">Y.<o:p></o:p></span></p>
                  </div>
                </div>
              </div>
            </div>
          </blockquote>
          <p class="MsoNormal"><span lang="EN-US"><br>
              Hmm, I would love that to be true. But I've seen so many
              so called "corner-cases" that I now think the failure area
              in a datacenter is a fractal with infinite corners. Yes,
              you could monitor SMART on local drives, pick up
              uncorrected ECC errors, use "sensors" to check for sagging
              voltages or high temps, but I don't think you can ever
              hope to catch everything, and you could end up doing a
              migration "storm" for . I've had more than enough of
              "Enterprise Spec" switches suddenly going nuts and
              spamming corrupt MACs all over the LAN to know you can't
              ever account for everything.<br>
              <br>
              I think it's better to adopt the model of redundancy in
              software and services, so no-one even notices if a VM host
              goes away, there's always something else to take up the
              slack. Just like the origins of the Internet - the network
              should be dumb and the applications should cope with it!
              Any infrastructure that can't cope with the loss of a few
              VMs for a few minutes probably needs a refresh.<br>
              <br>
              Cheers<br>
              <br>
              Alex<br>
              <br>
              <br>
              <br>
              <br>
              <br>
              . <o:p></o:p></span></p>
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