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From Jay Kreps <jay.kr...@gmail.com>
Subject Re: Kafka mirroring and zookeeper
Date Tue, 24 Apr 2012 20:42:14 GMT
Right now we do sloppy failover. That is when a broker goes down
traffic is redirected to the remaining machines, but any unconsumed
messages are stuck on that server until it comes back, if it is
permanently gone the messages are lost. This is acceptable for us in
the near-term since our pipeline is pretty real-time so this window
between production and consumption is pretty small. The complete
solution is the intra-cluster replication in KAFA-50 which is coming
along fairly nicely now that we are working on it.

-Jay

On Tue, Apr 24, 2012 at 12:21 PM, Oliver Krohne
<oliver.krohne@googlemail.com> wrote:
> Hi,
>
> indeed I thought could be used as failover approach.
>
> We use raid for local redundancy but it does not protect us in case of a machine failure,
so I am looking for a way to achieve a master/slave setup until KAFKA-50 has been implemented.
>
> I think we can solve it for now by having multiple broker so that the application can
continue sending messages if one broker goes down. My main concern is to not introduce a new
single point of failure which can stop the application. However as some consumer are not developed
by us and it is not clear how they store the offset in zookeeper we need to find out how we
can manage the consumer in case a broker will never return after a failure. It will be acceptable
to lose a couple of messages if a broker dies and the consumers have not consumed all messages
at the point of failure.
>
> Thanks,
> Oliver
>
>
>
>
> Am 23.04.2012 um 19:58 schrieb Jay Kreps:
>
>> I think the confusion comes from the fact that we are using mirroring to
>> handle geographic distribution not failover. If I understand correctly what
>> Oliver is asking for is something to give fault tolerance not something for
>> distribution. I don't think that is really what the mirroring does out of
>> the box, though technically i suppose you could just reset the offsets and
>> point the consumer at the new cluster and have it start from "now".
>>
>> I think it would be helpful to document our use case in the mirroring docs
>> since this is not the first time someone has asked about this.
>>
>> -Jay
>>
>> On Mon, Apr 23, 2012 at 10:38 AM, Joel Koshy <jjkoshy.w@gmail.com> wrote:
>>
>>> Hi Oliver,
>>>
>>> I was reading the mirroring guide and I wonder if it is required that the
>>>> mirror runs it's own zookeeper?
>>>>
>>>> We have a zookeeper cluster running which is used by different
>>>> applications, so can we use that zookeeper cluster for the kafka source
>>> and
>>>> kafka mirror?
>>>>
>>>
>>> You could have a single zookeeper cluster and use different namespaces for
>>> the source/target mirror. However, I don't think it is recommended to use a
>>> remote zookeeper (if you have a cross-DC set up) since that would
>>> potentially mean very high ZK latencies on one of your clusters.
>>>
>>>
>>>> What is the procedure if the kafka source server fails to switch the
>>>> applications to use the mirrored instance?
>>>>
>>>
>>> I don't quite follow this question - can you clarify? The mirror cluster is
>>> pretty much a separate instance. There is no built-in automatic fail-over
>>> if your source cluster goes down.
>>>
>>>
>>>> Are there any backup best practices if we would not use mirroring?
>>>>
>>>
>>> You can use RAID arrays for (local) data redundancy. You may also be
>>> interested in the (intra-DC) replication feature (KAFKA-50) that is
>>> currently being developed. I believe some folks on this list have also used
>>> plain rsync's as an alternative to mirroring.
>>>
>>> Thanks,
>>>
>>> Joel
>>>
>

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