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From Lennert den Teuling <lenn...@pcextreme.nl>
Subject Re: Basic Zone Virtual Router Issues
Date Mon, 11 Nov 2013 23:44:40 GMT
> Op 12 november 2013 om 0:07 schreef Nick Wales <nick@nickwales.co.uk>:
> 
> 
> I have a couple issues with the current setup involving the virtual router.
> 
> 1. I'm not using the VR for port forwarding / VPN / routing or anything
> traffic related so it would seem to me to be relatively trivial to have a
> secondary virtual router that just provides DNS, userdata & metadata. This
> would be sufficient for all my failover requirements.
> 
> 2. It would also be useful to be able to set DNS options in a basic zone.
> Timeout, attempts etc.  Timeout on linux is set to 5 seconds which is an
> eternity in case of failure.
> 
> Are people comfortable with a single VR in a basic zone, and what
> mitigations can be put in place to avoid any fallout from failures?

Hi Nick,

When the VR is down, you could run into some issues especially when you are
recovering from hardware failure. In this case the instances that are down will
not start until you fixed the router. This is quite logical cause they need DHCP
for example.

The router startup was quite slow in the past. We run about 400 VMs per pod, and
you will not be very happy when it takes about 1 hour to reconfigure all DHCP
entries. Luckily, the VR startup time has been improved a lot lately, and for us
the same process takes about 15 minutes but still, it could be faster in the
future.

So when the VR doesn't boot you cannot boot your other VMs which could be
problematic even if it takes only 15 minutes. Because of this we are planning to
move SSVMs (including the VR) to a seperate cluster so it doesn't run next to
instances of our clients so both cannot (or shouldn't) be offline at the same
time.

Anyway, if you plan to run like up to 50 instances in a pod (using the same VR),
this will won't be a problem for you cause VR startup time will probably be
acceptable.

When you recreate the VR (which you should be able to do whenever you want), it
will likely receive a new IP and you VMs need to renew their DHCP lease to
receive the new IP adres for DNS. This is why we have chosen not to use the DNS
server of the VR.

Hope this helps!

Met vriendelijke groet / Kind regards,

Lennert den Teuling
Tel direct: +31 (0)118 700 210

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