ESXi VM NTP Server

We need to setup an internal NTP server. Because this server will pretty much ONLY be a time server I was thinking of just creating a VM for it. However, Googling around it appears that there there might be serious clock drifting issues with VM servers. So, is running our NTP server in a VM a completely dumb idea?

Thanks, John

Time can be a problem inside VMs but by the same token if done correctly can be as accurate as a physical machine. It may seem odd but I'm a huge fan of using my switches (always Cisco in my world) as my NTP sources - not only are they easy to setup as such but it they have the handy benefit of being your DG too usually - see if your switches can do this too.

(This question might better fit on StackOverflow's sister site, ServerFault.com.)

Yes, clock drift can be more drastic on hosted virtual machines when compared with physical hardware. (Normally you would set the VMware host server to sync with your NTP server of choice, then have the VMware Tools in each of the virtual machines sync with their parent host.) But I'm not sure it's a reason to avoid a virtual NTP server...

On the other hand, have you considered other options? For example, NTP is such a lightweight service that it could be added to just about any other production server with no load increase. (Heck, if you have a Windows domain, one of your Active Directory controllers is already acting as an NTP server for the domain members.) Or, is it possible to use an existing NTP server from the Internet (see http://www.pool.ntp.org/en/ for a huge list)?

In general, running an authoritative NTP server on a VM is a very bad idea. It can be difficult enough just getting a VM to have a consistently accurate time, to within a second.

You really need to run it on metal of some kind, but as ewall said it's usually a light weight service (if it's only for internal usage). We generally combine it with some other kind of server already running on hardware, such as for example DHCP or DNS servers.

Set up at least two, make them peers of each others and synchronize them to a known set of good servers. What those might be depends on where you are; check with your ISP(s), national authorities on time, etc. Pool.ntp.org might be OK or might not be good enough, depending on your requirements.

Why not make use of the ntpd running on ESXi itself as your local ntp server?

Firstly setup your time sync as per normal on the ESXi host pointing to one or more external ntp servers (check out pool.ntp.org).

In order to allow other hosts to make use of ntpd running on ESXi you will have to add a custom firewall rule to allow it to be used as a server. The easiest way to add the firewall rules is by running the following at an ESXi shell:

esxcli software acceptance set --level CommunitySupported
esxcli software vib install -v http://files.v-front.de/fwenable-ntpd-1.2.0.x86_64.vib

Once complete simply tick the box next to "NTP Daemon" in your ESXi servers Firewall Properties. Now you can have your cake and eat it too!

Source: http://www.v-front.de/2012/01/howto-use-esxi-5-as-ntp-server-or-howto.html