Monday, 9 December 2013

Re: Ubuntu Server seeded package review

On 12/09/2013 11:50 AM, Serge Hallyn wrote:
> Chris Arges (cc:d) has looked into this before in-depth. But I don't
> seem to have the email with his conclusions. Chris, could you summarize
> here what you had found when you looked into our previous suggestion to
> not enable ntp in guests?
>

Hi,

Here is the original thread about this topic:
https://lists.ubuntu.com/archives/ubuntu-server/2013-April/006556.html

Originally we had recommended _not_ to use NTP on VMs, but after
researching this a bit further it seemed clear that NTP should work
perfectly fine. The modification I made is updated here:
https://help.ubuntu.com/community/KVM/FAQ#Should_ntp_be_used_for_time_synchronisation.3F

My statement was pretty vague on purpose.
If you are doing lightweight stuff when you boot the VM the kvmclock
will setup the clocksource just fine and we expect the system time to
not drift too much while the VM is up.
For heavy duty stuff where you have many VMs, they run for a long time ,
or never shutdown/reboot the machine, it makes sense to setup NTP client
on the VM using the host machine as the ntp server.

> Quoting Seth Arnold ([email protected]):
>> On Thu, Dec 05, 2013 at 05:15:41PM -0600, C de-Avillez wrote:
>>> Although I am probably hammering a rather cold iron, I still fail to
>>> understand why ntp is not installed by default. I would expect precise
>>> timekeeping to be something important on a server (instead of allowing
>>> the time to drift slowly).
>>
>> I would like to hear from An Expert if ntpd, ntpdate, ptpd, etc., are
>> reasonable things to install in virtual machine guest environments.
>>
>> My personal suspicion is that when a virtual machine host runs ntpd,
>> guests should not run ntpd, since two daemons attempting to skew the
>> clock sounds like a recipe for highly chaotic behavior. ntpdate would
>> be alright since it does not attempt to manage clock skew. ptpd no idea.
>>

This is why the guest should use the host as the ntp server. Instead of
both reaching out to ntp.ubuntu.com for example.

>> When the virtual machine host does not run ntpd, I suspect ntpd, ntpdate,
>> ptpd, are all fine things to run in the guests.
>>
>> I'd love to know for certain what the best practices are. It might
>> influence the default package installs.
>>

I posted this earlier on ubuntu-server ML because I wasn't an expert. So
I'm open to other suggestions on how to accomplish this.

--chris j arges

>> Thanks
>
>
>
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