[Users] Hosted-Engine purpose for gateway check?

[Itamar Heim]

On 04/06/2014 10:20 AM, Andrew Lau wrote:
> On Sun, Apr 6, 2014 at 4:55 PM, Yedidyah Bar David <didi at redhat.com> wrote:
>> ----- Original Message -----
>>> From: "Andrew Lau" <andrew at andrewklau.com>
>>> To: "users" <users at ovirt.org>
>>> Sent: Sunday, April 6, 2014 3:10:19 AM
>>> Subject: [Users] Hosted-Engine purpose for gateway check?
>>>
>>> Hi,
>>>
>>> I was recently playing around with the new ovirt 3.4 ga, I'm very
>>> happy all those issues I reported got fixed :D
>>>
>>> I found a new issue regarding the use of PREFIX vs NETMASK which I've
>>> uploaded here https://bugzilla.redhat.com/show_bug.cgi?id=1084685
>>>
>>> Anyway -- I'm wondering what is the purpose for the gateway check in
>>> the hosted-engine setup? In my test case, I had the following NIC
>>> configuration
>>>
>>> eth0 - public (has gateway)
>>> eth1 - management
>>> eth1.1 - storage
>>> eth2 - vm data (no IP address)
>>>
>>> So during the hosted engine install, it will not let me assign eth2 as
>>> the NIC because it has no IP address or gateway. So I proceed to use
>>> eth1 instead as, as it has an IP address but again that would fail
>>> because no gateway. Luckily I have a L3 switch, so I put up a gateway
>>> for eth1 and that solved that issue.
>>>
>>> What is the gateway check supposed to achieve? I also tried to put in
>>> my eth0's IP address as the gateway but it still failed because of
>>> those config issues. If management/ovirtmgmt/vmdata are all on a L2
>>> switch environment, effectively there becomes no gateway and it
>>> prevents the installation.
>>
>> It actually does not need to really be a gateway. It's used only as
>> part of a calculation trying to assess the liveliness of the host.
>> See [1] for details, especially pages 33-34.
>>
>> [1] http://www.ovirt.org/images/8/88/Hosted_Engine_Deep_Dive.pdf
>> --
>> Didi
>
> I've recall reading that pdf before - however my comments are a little
> aimed towards why does the setup require the GATEWAY=x be in the
> ifcfg-ethx file when it also asks for the gateway in the otopi setup.
> It seems a little redundant and also prevents the ability to proceed
> with the setup if you're in a L2 switch environment.
>
> The hosted-engine VM will require a gateway as it only has one nic and
> needs to be publicly accessible, so let's say we have:
> eth1 -> ovirtmgmt (172.16.0.10) -> hosted-engine (192.168.100.10 w/
> 192.168.100.1 as gateway)
>
> Isn't 192.168.100.1 the gateway we want to be checking for?
>
> Although now that I think of it, I'm confused where the gateway check
> has it's example scenario, is it just for checking to make sure the
> hosted-engine will be externally accessible? Wouldn't it also work to
> do something like ethtool and check the link exists instead.
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As didi explained the remote "gateway" for hosted engine liveliness is 
meant so the host running the hosted engine can also check it has 
network connectivity to some well known IP. if it doesn't have it, it 
will reduce its score, so if another host does have connectivity to that 
remote IP, it will become the preferred host to run hosted engine.