[ovirt-users] Some questions about Ovirt architecture

[Gianluca Cecchi]

Disclaimer: These are preliminary answers. I'm not part of oVirt team ;-)


On Wed, Aug 23, 2017 at 10:05 AM, Khoi Thinh <thinhduckhoi at gmail.com> wrote:

> Hello,
>
> My name is Khoi. I'm totally new to Ovirt and i'd like to know some
> knowledge related to Ovirt's architecture as well as how it works.
> As far as i understand, in each "Node" we can have many "guest".
> My questions are:
>
> 1.We need to install Ovirt management engine in order to manage system.
> But that engine would be installed on "Node" or can be installed on "Guest"?
>

There are 2 scenarios:

- engine is kept separate from oVirt infra itself. In this case the related
sw components should be installed on a server that is not one of the nodes
an not one of its guests. This server could be a physical server or a
virtual server (in this second case part of a different virtual
infastructure, oVirt or not oVirt)
Eg: I have a vSphere environment where I configured a CentOS 7.3 VM and on
it I installed the engine sw components for managing an oVirt
infrastructure. So this vSphere virtual machine is my "oVirt management
engine", using your words.
HA of this server and its backup/restore policies naturally inherited from
what offered by VMware and its agents

- engine is itself a VM of the oVirt infrastructure that it has to manage
This kind of environment is known as Self Hosted Engine environment
The technological approach is similar to the one described here for VMware:
https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=10087

There is also the choice to use an already set-up virtual appliance as done
in VMware:
https://docs.vmware.com/en/VMware-vSphere/6.0/com.vmware.vsphere.vcsa.doc/GUID-223C2821-BD98-4C7A-936B-7DBE96291BA4.html

See here for oVirt:
http://www.ovirt.org/documentation/self-hosted/chap-Deploying_Self-Hosted_Engine/

and here for RHEV:
https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/html/self-hosted_engine_guide/deploying_self-hosted_engine



> 2.Let's say i have 2 "Node" with 4 "Guest" in each "Node"
> It would be something like this
> [ ■  ■] Node 1
> [ ■  ■]
>
> [ ■  ■]  Node 2
> [ ■  ■]
>
> If the management engine can be installed on the first guest of Node1,
> from that we can manage everything in Node1 and Node2? Or we just only
> manage the other guest in Node1?
>

When you use Self Hosted Engine Environment, the guest used as engine mgmt
virtual server is not "owned" by a particular host.
In a certain moment in time it will run on Node1 or Node2 but it can be for
example live migrated if you desire.
A subset of the Hosts of the infrastructure can be selected as "Hosted
Engine" Hosts, so to be able to guest the engine VM
You should define at least more than one hosts of this kind, if you want
redundancy for the engine vm in this case.

See here the RHEV doc to add a new host and set it as an "hosted engine"
host, I don't find the related part in oVirt docs (link missing...)

https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.1/html/self-hosted_engine_guide/chap-installing_additional_hosts_to_a_self-hosted_environment
Feel free also to RTFM.. both oVirt and RHEV, they are done well in my
opinion, starting here:
https://access.redhat.com/documentation/en/red-hat-virtualization?version=4.1/

the match is not 1-1 between oVirt and RHEV same versions but I would say
at least 90%


>
> 3.Regard of High availability of Ovirt
> If the first guest of Ovirt1 (which we install management engine on) went
> down, what would happen? We can pull a image from Shared Storage and use it
> to deploy a new management engine on other Guest? (On Node1 or Node2)
>

Based on the answers above, this applies only in self hosted engine
scenario, and as written above, you should take care of setting more than
one host as "hosted engine" host, so that the HA of the engine VM will be
guaranteed.
I opened a bug to propose this to be the default in case of self hosted
engine environment.
See here
https://bugzilla.redhat.com/show_bug.cgi?id=1399613

and also this related one:
https://bugzilla.redhat.com/show_bug.cgi?id=1399609



>
> Best regards,
>
>
> --
> *Khoi Thinh*
>
> _______________________________________________
> Users mailing list
> Users at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/users
>
>
Cheers,
Gianluca
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ovirt.org/pipermail/users/attachments/20170823/8e0b8734/attachment.html>