zookeeper-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Andor Molnar <an...@cloudera.com>
Subject Re: Kafka Failing to start due to existing ID
Date Wed, 13 Jun 2018 11:42:23 GMT
Hi Harish,

I see 2 things which need to be clarified here:

1. ZooKeeper session dies in 2 cases only: when client explicitly closes
the session (which is *not* equivalent to disconnection) or session timeout
expires,
2. If quorum is not present, there'll be no updates committed and clients
are rejected to connect, so Kafka shouldn't be able to use the cluster.

Similarly, when quorum comes back online, ZooKeeper will continue operating
normally: it receives client connections, performs updates and expire
sessions if necessary.

I still believe therefore that your Kafka setup doesn't properly cleanup
znodes for some reason, but I'm not a Kafka expert.

Regards,
Andor




On Wed, Jun 13, 2018 at 12:34 AM, harish lohar <hklohar@gmail.com> wrote:

> Exactly , so in a case where there is jo quotum and no update can be made ,
> is there a way yo stop kafka failing to start.
>
> One way is to cleanup kafka related znodes  after bringing up quorum and
> then starting kafka.
>
> I was looking to avoid this.
>
>
> On Tue, Jun 12, 2018 at 4:59 PM Brian Lininger <brian.lininger@veeva.com>
> wrote:
>
> > Hi Harish,
> > I think I see what may be the problem for you.  Based on your initial
> > description (6 ZK nodes, 3 down) I think the problem is that you no
> longer
> > have a quorum.  When a Zookeeper cluster is running, updates (i.e.
> removing
> > znodes) can only occur when Zookeeper has a quorum, which 50.1% of the
> > configured Zookeeper nodes.  If I understand correctly, then in your case
> > you have 6 Zookeeper nodes configured but 3 are down.  This means that
> you
> > only have 50.0% of the Zookeeper cluster working, and thus Zookeeper does
> > not have a quorum so no updates can be made.  I don't know much about the
> > new TTL feature in 3.5, but my assumption is that it works on this same
> > principle which is that no updates can be made to the cluster's znodes
> when
> > there is no quorum.  The same applies to the 3 Zookeeper node cluster,
> you
> > must have 2 nodes running to form a quorum and allow any updates to
> occur.
> >
> > Please correct me if I missed something....
> >
> > Thanks,
> > Brian
> >
> >
> > On Tue, Jun 12, 2018 at 1:33 PM, harish lohar <hklohar@gmail.com> wrote:
> >
> >> ---------- Forwarded message ---------
> >> From: harish lohar <hklohar@gmail.com>
> >> Date: Tue, Jun 12, 2018 at 3:26 PM
> >> Subject: Re: Kafka Failing to start due to existing ID
> >> To: <andor@apache.org>
> >>
> >>
> >> Hi Andor,
> >>
> >> Thanks for your reply.
> >>
> >> This issue is irrespective of number of nodes, even should be seen with
> 3
> >> Node cluster as well.
> >>
> >> Actually kafka has session_timeout config , but that seems to be in
> effect
> >> only if zookeeper cluster is up i.e. if kafka goes down when zookeeper
> >> cluster is up.
> >>
> >> Now let's say if 2 nodes of Zookeeper cluster is down , and then if
> kafka
> >> connected to 3rd Zookeeper Node goes down zookeeper cluster doesn't
> >> refresh
> >> the session for Kafka connected to 3rd Node.
> >>
> >> So when other Node comes up and zookeeper cluster becomes available it
> >> doesn't delete the id of the kafka which went down when zookeeper
> cluster
> >> was down.
> >>
> >> Regarding TTL I have already enquired the kafka forum and awaiting
> reply.
> >>
> >> Ideally once zookeper cluster is up , it should delete the kafka broker
> >> id's which are not connected which doesn't seem to be happening
> >>
> >> I hope I am making some sense :)
> >>
> >> Thanks
> >> harish
> >>
> >>
> >>
> >> On Tue, Jun 12, 2018 at 2:59 PM Andor Molnár <andor@apache.org> wrote:
> >>
> >> > Hi Harish,
> >> >
> >> >
> >> > I have a few questions to get some insight about your issue.
> >> >
> >> > 1. Why do run ZooKeeper with 6 nodes while odd number of nodes are
> >> > recommended (not an issue really, just for curiousity),
> >> >
> >> > 2. Does Kafka support ZK 3.5+ with TTL nodes?
> >> >
> >> > I think this is more of a Kafka question, but afaik Kafka doesn't run
> >> and
> >> > cannot take advantage of 3.5 only features of ZK. Maybe I'm wrong,
> but I
> >> > think it has some cleanup mechanism to delete expired broker ids or
> you
> >> > must wait for the session to expire.
> >> >
> >> >
> >> > Regards,
> >> >
> >> > Andor
> >> >
> >> >
> >> >
> >> > On 06/12/2018 04:39 PM, harish lohar wrote:
> >> >
> >> > Hi All,
> >> >
> >> > Need help regarding below scenario if any configuration is available
> to
> >> > help.
> >> >
> >> > I have cluster of 6 nodes
> >> > 3 Nodes are stopped and  brought up again, kafka fails to restart
> since
> >> > broker ID are still present in zookeeper znode /broker/ids/
> >> >
> >> > Since the cluster goes down after removing 3 Nodes , session timeout
> >> > doesn't happen.
> >> >
> >> > Though i am aware about TTL feature in zookeeper , but how to make
> sure
> >> > kafka creates znodes with TTL
> >> >
> >> > Thanks
> >> > Harish
> >> >
> >> >
> >> >
> >> >
> >>
> >
> >
> >
> > --
> >
> > [image: Veeva Systems - Zinc Team]
> >
> > *Brian Lininger*
> > Technical Architect, Infrastructure & Search
> > *Veeva Systems *
> > brian.lininger@veeva.com
> > www.veeva.com
> >
> > *This email and the information it contains are intended for the intended
> > recipient only, are confidential and may be privileged information exempt
> > from disclosure by law.*
> > *If you have received this email in error, please notify us immediately
> by
> > reply email and delete this message from your computer.*
> > *Please do not retain, copy or distribute this email.*
> >
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message