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From Anuj Wadehra <>
Subject Re: Configure NTP for Cassandra
Date Wed, 14 Dec 2016 18:02:02 GMT
Thanks Martin. Agree, setting up our own internal servers will help save some firewall traffic,
simplify security management and reduce load on public servers which is an ethical thing to
do. As the blog recommended setting up own internal servers for Cassandra, I wanted to make
sure that there are no Cassandra specific benefits e.g. better relative time synchronization
achieved with an internal setup. So, I would conclude it this way : Even though its not a
good practice to directly access external NTP servers via Cassandra nodes, Cassandra can still
achieve tight relative time synchronization using reliable external servers. There is no madate
to setup your own pool of internal NTP servers for BETTER time synchronization.
Thanks for your inputs.Anuj 
  On Wed, 14 Dec, 2016 at 3:22 AM, Martin Schröder<> wrote:   2016-11-26
20:20 GMT+01:00 Anuj Wadehra <>:
> 1. If my ISP provider is providing me a pool of reliable NTP servers, should
> I setup my own internal servers anyway or can I sync Cassandra nodes
> directly to the ISP provided servers and select one of the servers as
> preferred for relative clock synchronization?

Set up three ntp servers which uses the provider servers _and_ pool servers
and sync your other machines from these servers (and maybe get gps receivers
for your ntp servers). This reduces ntp traffic at your firewall (your servers
act as proxies) and reduces load on public servers.

> 2. As per my understanding, peer association is ONLY for backup scenario .
> If a peer loses time synchronization source, then other peers can be used
> for time synchronization. Thus providing a HA service. But when everything
> is ok (happy path), does defining NTP servers synced from different sources
> as peers lead them to converge time as mentioned in some forums?

Maybe; but the difference will be negligible (sub milliseconds).
I wouldn't worry about that.


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