[ovirt-users] Autostart VMS

Fri Apr 8 21:07:10 UTC 2016

On Fri, 2016-04-08 at 21:50 +0300, Nir Soffer wrote:
> On Fri, Apr 8, 2016 at 9:33 PM, Brett I. Holcomb 
> m> wrote:
> > 
> > On Fri, 2016-04-08 at 19:25 +0300, Nir Soffer wrote:
> > 
> > On Fri, Apr 8, 2016 at 7:17 PM, Brett I. Holcomb 
> > com>
> > wrote:
> > 
> > On Fri, 2016-04-08 at 11:31 +0200, Martin Sivak wrote:
> > 
> > Hi,
> > 
> > 
> > I set highly available on, did not pin to any host, and also set
> > the
> > watchdog which should reset if they go down but I'm not sure that
> > will start
> > them if the host comes up and the VMs are not running.  I'll look
> > at the CLI
> > first.
> > 
> > 
> > The engine will try to keep the VM running. So if one host goes
> > down,
> > it will restart the VM on some other host automatically. We will
> > also
> > migrate the VM (or some other to free resources) when the current
> > host
> > gets too loaded. We do not require any migration addons, it just
> > works. But of course we have usually more hosts in a cluster to
> > make
> > this possible.
> > 
> > I do not really remember what happens when all hosts are restarted
> > (power outage) though as that is quite special case.
> > 
> > Regards
> > 
> > --
> > Martin Sivak
> > SLA / oVirt
> > 
> > 
> > 
> > Thanks.  I only have one host so who knows what will happen.  I'm
> > working on
> > a script that will basically emulate what VMware does - start VMS
> > in a given
> > order at startup of the host/engine.  I'll also file a feature
> > request.
> > 
> > 
> > Why do you care about the order?
> > 
> > Isn't it enough to restart all the vms after a host was restarted?
> > 
> > Nir
> > 
> > 
> > Does the Engine start all VMs after the host is powered up and the
> > engine
> > running if I set a watchdog on a VM?  I know it will try to restart
> > the VM
> > if it goes down once oVirt is up and running.   If it will start
> > the VMs at
> > reboot time that helps.
> I think only HA vms are restarted. Adding Michal to add more info on
> this.
> 
> > 
> > The reason for the order is that you need some servers such as DNS,
> > file
> > servers, up first before other systems can resolve addresses or
> > mount
> > shares.  For Windows you need domain controllers running before the
> > other
> > windows systems that are part of the domain.  For applications such
> > as Lotus
> > Notes the servers had to come up in the correct order.
> Lets say you have a way to order the vms when some vms are down.
> 
> What will happen to when dns, file servers or domain controller will
> crash?
> Do you have to restart all the vms depending on them or they can
> recover and detect that vm they depend on were restarted?
> 
> Seems that what you need is a systemd for your data center - every
> host define the host it depends on, and the system generate the
> correct order to start the vms, starting vms in the same time when
> possible.
> 
> Please reply also to the list, this thread may be useful to others.
> 
> Nir
Hopefully this will go to the list as i"ve been making sure users at ovirt
.org is in the To field.
I think we need to make sure we distinguish between the start up phase
and the running phase which is what happens after everyone is up and
running happily.  Based on my experience the crash of a server is
considered separately from startup. 
As mentioned in my response to the list to someone else's comment the
startup sequence is the same as people flipping switches on physical
servers following a documented procedure to start or shutdown a
datacenter as we did in the "old days".  With physical boxes we had to
shutdown/startup manually and we did it in a sequence that we had
written down.  With virtualization and since we had VMware we could
automate that process so as we spun up the hosts VMware started
spinning up the guests in the order specified so we got our DNS boxes
up first, then others.  For Active Directory we started the domain
controllers first, then other servers such as file servers, application
servers in the sequence needed for the applications to run.
Crashing of DNS, File Server, Domain Controllers crashing after the
datacenter is up and running is handled (or should be) by redundancy of
servers or process the service provides.  You have multiple DNS servers
and the resolver will try the secondary/tertiary/whatever if the
primary is down.  File servers are the same.  For Gluster, CephFS, MS
DFS you have (or should have setup) the ability to keep running if one
of the servers goes down.  A redundant file server setup will handle a
server crash.  For Domain Controllers you should have at least two (we
had six in our environment) and when one goes down the others keep the
domain running by shifting the services to others and continuing to
provide authentication, etc.  Generally what we did when a domain
controller crashed is fix it if possible and if it was not fixable pull
it's pieces out of the domain and spin up a new one.   Same for DNS or
file servers.  When they go down find out why, fix it or replace the
server, and get the service redundant again.  Also, oVirt has the
watchdog function so if a VM goes down it will try and restart it.  If
it can't restart then we're dealing with a crashed server which we
should have provided for in our data center design.
My wish is to have oVirt allow us to do what VMware does and allow us
to say start/don't start these servers up in the order I specify so
that when the Engine is ready it looks at the list and begins turning
on VMs in the order specified.  Shutdown is done in the reverse order).
 For large datacenters with many VMS manual startup is a pain.  Once
it's running rely on good practices of having redundant servers (i.e.
more than one DNS), file servers that can handle the failure of a
server, multiple domain controllers which is not something we need to
burden oVirt with.  Handling of failures needs to be done by the people
in charge who are supposed to design the data center based on their
risk/cost analysis. 
If I  understand what you said - I'm not sure we have to define a
dependancy list where we define dependancies like we would with systemd
or a package manger.  It doesn't need to be complex since just a simple
list of priority: VM id/name pairs will work. All we need is to be able
to say "start these VMs when the Engine is ready".  The order or
dependency is set by where I put the VM in the list.  If it's at the
top start it first, then move to the second one, and so on.  There can
be settings for delay between starting VMs and how long to wait for a
VM to come up before assuming it's dead and moving on to the next.
 Tasking oVirt with the job of figuring VM dependancies would be a
nightmare for oVirt and whoever had to program it <G>.  We as data
center administrators should be handling that task.  Yes, we manually
set the list but trying to automate a dependancy chain would be pretty
difficult.
I envision a web admin portal GUI where we define a simple list of VMs
that we want the Engine to autostart. We need to be able to move them
up/down the list.  The list is stored somewhere for the Engine
(database?, whatever else the Engine has as storage areas - not really
familiar with the Engine internals) and when the Engine is up and ready
to start VMs it retrieves the list and starts at the first VM in the
list and starts it, waits some time (0-?? seconds), and then moves on
to the next one.  If the VM hasn't started in the set time the Engine
moves on to the next one.
Note that Microsoft's Hyper-V also provides automatic VM startup but it
is done on a VM level where you just tell the VM to start whenthe Hypr-
V starts.  If you want sequencing you have to set time delays.  Auto
 start up is better than nothing but Hyper-V is a nightmare trying to
sequence VMs.
I think VMware did it right in allowing both autostart and being able
to sequence the startup of VMS so it's host independent.  As
information VMware also allowed delays between VM startups as does
Hyper-V.
> > 
> > On Wed, Apr 6, 2016 at 9:10 PM, Brett I. Holcomb <biholcomb at l1049h.com>
> > >
> > wrote:
> > 
> > On Wed, 2016-04-06 at 13:42 -0400, Adam Litke wrote:
> > 
> > On 06/04/16 01:46 -0400, Brett I. Holcomb wrote:
> > 
> > In VMware we could setup guests to autostart when the host started and
> > define the order.  Is that doable in oVirt?  The only thing I've seen
> > is the watchdog and tell it to reset but nothing that allows me to
> > define who starts up when and if they autostart.  I assume it's there
> > but I must be missing it or haven't found it in the web portal.
> > 
> > 
> > In oVirt guests aren't tied to a host by default (although you can set
> > them to run only on a specific host if you want).  The closest thing I
> > can think of would be the High Availability features (VM->Edit).
> > oVirt will try to restart highly available VMs if they go down.  You
> > can also set the priority for migration and restart in that pane.
> > Hopefully a combination of host pinning and the  high availability
> > settings will get you close enough to where you want to be.
> > 
> > Otherwise, you could always do some scripting with the ovirt REST API
> > using the SDK or CLI.
> > 
> > 
> > If you had the VMware migration extra add-on you could have hosts move as
> > needed so they were not tied to any host either but we could set a startup
> > order and specify auto, manual so that once the host started the VMs were
> > brought up as specified no matter what host they were running on.
> > 
> > I am running hosted-engine deployment with the Engine VM on the host.
> > 
> > I set highly available on, did not pin to any host, and also set the
> > watchdog which should reset if they go down but I'm not sure that will start
> > them if the host comes up and the VMs are not running.  I'll look at the CLI
> > first.
> > 
> > It would be nice if oVirt added this feature as it's really required for
> > large installations and is a help for any size installation, even small
> > ones.
> > 
> > 
> > 
> > 
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