I seem to recall discussing at one point the idea of setting multiple time sources with a fallback behavior between them. In other words, the default could be the built-in client, but in the case that the built-in client can't contact NTP servers, we would fall back to the system NTP. This switching behavior could be dynamic (eg it would switch back when system NTP is down). Has this been considered and ruled out for some reason?
-Todd On Mon, Mar 16, 2020 at 9:51 PM Adar Lieber-Dembo <[email protected]> wrote: > I share the two concerns you highlighted, Alexey. > 1. This would be a backwards incompatible change. > 2. The default NTP server list could be unreachable, or could be a > poorer choice than whatever the cluster is currently using. Grant's > suggestion could mitigate that somewhat, but it's sort of weird for > Kudu to go rooting around in system configuration files, not to > mention the possibility that we could get it wrong. > > To that I'll add a third concern: > 3. The build-in NTP client has an awful lot of TODOs. Does it work > correctly when NTP servers misbehave? I presume chronyd and ntpd are > battle-tested in this regard. > > Taken together, I'd be hesitant to change the default time source, at > least not without more concrete feedback suggesting that it'd be an > improvement for the vast majority of our user base. Ad hoc switching > is always an option when the system time source doesn't work. > > On Mon, Mar 16, 2020 at 8:12 PM Grant Henke <[email protected]> > wrote: > > > > > > > > Also, in > > > case of Kudu clusters running without access to the internet, it will > be > > > necessary to point the built-in NTP client to some internal NTP servers > > > since pool.ntp.org servers (the default servers for the built-in NTP > > > client) might not be accessible. > > > > > > > I think this was discussed at some point, but I don't remember the > > outcome/answer. > > Would it be possible to load the ntp servers from /etc/ntp.conf > > or /etc/chrony.conf if --builtin_ntp_servers > > aren't specified? We could still fall back to the default pool.ntp.org > if > > an ntp configuration isn't found. > > Looking in two files isn't great, but we could give preference to > > chrony.conf. > > > > Thank you, > > Grant > > > > > > On Mon, Mar 16, 2020 at 9:16 PM Alexey Serbin <[email protected]> wrote: > > > > > Hi, > > > > > > I'd like to get feedback on the subj, please. > > > > > > The built-in NTP client for Kudu masters and tablet servers was > introduced > > > in Kudu 1.11.0. Back then, there were thoughts of switching to the > > > built-in client by default starting Kudu 1.12. > > > > > > Since it's time for cutting 1.12 release branch pretty soon, I think > it's a > > > good opportunity to clarify on whether we want to make that change or > we > > > want to keep the time source as is (i.e. 'system') in 1.12 release. > > > > > > For more context, the built-in NTP client has been used to run external > > > mini-cluster-based test scenarios since 1.11.0 release for every gerrit > > > pre-commit build. In addition, I ran a 6 node cluster for a few weeks > at > > > two clusters cluster in public cloud with basic write/read workload > ('kudu > > > perf loadgen' with the --run_scan option). So far I've seen no issues > > > there. As for the use in a production environment, at this point I'm > not > > > aware of any Kudu clusters running in production using the built-in NTP > > > client. > > > > > > The benefit of the internal built-in NTP client is that it allows to > run > > > Kudu without the requirement of having the local machines' clocks > > > synchronized by the kernel NTP discipline. That might benefit newer > Kudu > > > installations where machines' clocks are not synchronized > out-of-the-box > > > and users are not keen performing an extra step deploying NTP servers > (and > > > configure them appropriately if the default configuration is not good > > > enough -- e.g., in case of fire-walled internal clusters). > > > > > > If we switch to the 'builtin' time source by default (i.e. use the > built-in > > > NTP client), existing installations running with the 'system' time > source > > > will need to add an extra flag if it's desired to stay with the > 'system' > > > time source after the upgrade to 1.12. In that regard, the update > would > > > not be backwards-compatible, but Kudu users should not care much about > the > > > clock source assuming the built-in NTP client is reliable enough. > Also, in > > > case of Kudu clusters running without access to the internet, it will > be > > > necessary to point the built-in NTP client to some internal NTP servers > > > since pool.ntp.org servers (the default servers for the built-in NTP > > > client) might not be accessible. > > > > > > So, it seems enabling the built-in NTP client by default could benefit > > > newer installations, but might require extra configuration steps for > > > existing Kudu deployments where pool.ntp.org NTP servers are not > > > accessible. The latter step should be described in the release notes > for > > > 1.12 release, of course. Also, there is some risk of hitting a not-yet > > > detected bug in the built-in NTP client. > > > > > > Do you think the benefits of removing the requirement to have the local > > > clock synchronized by local NTP server outweighs the drawbacks of > adding an > > > extra configuration step during 1.12 upgrade for Kudu clusters isolated > > > from the Internet? > > > > > > Your feedback is highly appreciated! > > > > > > > > > Thanks, > > > > > > Alexey > > > > > > > > > P.S. I sent the original message one week ago, but it seems it went > into > > > spam box or alike, so I'm re-sending it. > > > > > > > > > -- > > Grant Henke > > Software Engineer | Cloudera > > [email protected] | twitter.com/gchenke | linkedin.com/in/granthenke > -- Todd Lipcon Software Engineer, Cloudera
