[ntp:questions] [help]how to configure ntp in a private network and without extra refer clock source?

William Unruh unruh at invalid.ca
Wed Jul 16 02:03:58 UTC 2014

On 2014-07-16, john.wang.wjq at gmail.com <john.wang.wjq at gmail.com> wrote:
Please stop using google as your netnews host. They insert a blank line
between every line of quoted text making things unreadable. 
> On Monday, July 14, 2014 4:31:28 PM UTC+8, David Woolley wrote:
>> You are trying to do two undesirable things at once:  run a a time 
>> island; and directly update the clocks on VM guests.  I don't think this 
>> should be attempted without individual consultancy from someone with 
>> detailed knowledge of the VM system in use.
He says two things-- Only try to discipline the time on real machines,
not virtual machines. Do not run ntpd on any virutual OS. Have the
virtual OSs get their time from the underlying real hardware, and use
ntpd to discipline the real clocks on the real hardware.
iThis is true of ALL machines, whether your ntp servers or clients. 
Secondly use orphan mode under ntpd. Read up about it. 
>> Generally, the recommended way of handling time islands these days is to 
>> use a core network which peer each other and which use orphan mode to 
>> allow isolated operation.  These should be chosen to have good and 
>> accurate clocks against UTC when free running.
>> The general approach for VMs is to synchronise the hosts and then use 
>> whatever mechanism the VM environment provides to synchronised the 
>> guests, possibly with the occasional resynch.  You should advice from 
>> the VM environment provider as to how best to do this on their systems.
> Thank you David, I'm new to this field and I can hardly get any consultancy except asking on the web. Actuall we build the VM cluster ourselves to handle bigdata processing.
> What I'm trying to do is to keep time synchronized across the cluster. Either the time is correct or not, so long as all the nodes have the same time, it's fine. 
> I think I'm just following the approach you mentioned: use several physical hosts to build a time source to which all the nodes(vms) can synchronize.
>> use a core network which peer each other and which use orphan mode to allow isolated operation.
> I cannot grasp the points here. Do you mean to use several orphan ntp servers which peer each other ? Not sure if I'm understanding right, but the following is what I'm trying to achieve:
>     |--vm1
> A-B |--vm2
>| | |--..
> C-D |--..
>     |--vmN
> A,B,C,D are four ntp servers peer to each other. All the VMs are ntp clients(with ntpd running on them) synchronizing time with this four. Just like Jun Hu, using 4 ntp servers is just for HA.
> I think we may use a GPS as an external time source on this isolated network, but since we are just in testing stage, it's not really important for now i think.
> Thanks and Regards
> John

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