[ntp:questions] NTP in a Linux cluster

Lorcan lorcan.hamill at gmail.com
Mon Sep 7 18:17:28 UTC 2009


Folks,

Could any NTP experts suggest how I should best configure NTP in
a loosely-coupled Linux cluster, where intra-cluster synchronization
is
the top priority?

I have done some reading about NTP, but can't seem to find an
authoritative
guide to using NTP in a cluster environment.  My company sells systems
that
run on small clusters of Linux servers - typically from 2 to 16
servers ("nodes"),
each running RedHat Linux.  All nodes in a cluster are equal.  We
don't use
any third-party clustering software, just the standard OS and our own
applications.

The main priorities are:

1)  Time must be kept closely synchronized between all nodes in the
cluster.

2)  If one or more nodes become unavailable, synchronization must
still be
     maintained.

3)  Time must never go backwards, or jump - all changes must be by
"slewing"

4)  Time should track one or more external NTP servers as closely as
possible,
      while observing (1) to (3) above.

The key requirement here is the as-close-as-possible synchronization
between
nodes in the cluster; that is far more important than closely tracking
the external
NTP server(s).

How would an NTP guru go about configuring a cluster to meet those
requirements?

It would be preferable if the configuration of all nodes could be
identical.   A solution
that requires two or more node types ("master" and "slave" perhaps)
with different
settings would be acceptable, of course, if the preferred one-size-
fits-all approach
is impossible.

Should all nodes have configuration entries for all other nodes as
"peers"?

Should all nodes (or only one) have configuration entries for the
external NTP server(s)?

If all nodes have both peer and external server entries, how can I
arrange that
keeping in sync with peers is seen as more important than keeping in
sync with
the external servers?

Questions, questions...

Any and all answers would be gratefully received!

Thanks in advance,

Lorcan Hamill




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