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From ed <edor...@gmail.com>
Subject Re: Channel management: messages that will never be delivered
Date Wed, 05 Feb 2014 23:12:46 GMT
Hi Paul,

Not sure if this would work for you but if you can error check prior to the
events reaching Elasticsearch you can handle this by writing a custom
Interceptor that validates your events.  You can do more robust error
checking here than you can by just relying on the already existing event
header fields as you'll have full access to the event header and body.
 Within the interceptor, if the event is not compatible with Elasticsearch
you can add a boolean flag to the header of the event like "hasError".
 Then you can route any events that have an error to a different "error"
channel using a multiplexing selector by checking for the hasError flag.
 The error channel can either be connected to a NullSink or a FileRoll sink
if you want to preserve the improperly formatted events.

We've only used the memory channel so far so I'm afraid I can't comment on
the file channel specific questions you have.  Hopefully someone on the
list with some more experience there can chime in.



On Wed, Feb 5, 2014 at 5:34 PM, Paul Merry <paul.merry@bbc.co.uk> wrote:

>   Hi,
> We are using an Elasticsearch sink and have seen a file channel filling
> with messages that will never be delivered as the format of the message is
> incompatible with Elasticsearch itself.
> Example message from Flume logs:
> 24 Jan 2014 08:14:55,173 ERROR [SinkRunner-PollingRunner-DefaultSinkProcessor]
> (org.apache.flume.SinkRunner$PollingRunner.run:160)  - Unable to deliver event.
> Exception follows.
> org.elasticsearch.indices.InvalidIndexNameException: [UpperCase-2014-01-23]
> Invalid index name [UpperCase-2014-01-23], must be lowercase
> In this case the index name comes from a header so we have a workaround
> using a multiplexing channel selector to detect and re-route messages based
> on headers of this format.
> To clean up the channel this time we removed the data and checkpoint
> directories, which is not ideal as we probably lost other messages in doing
> this.
> We are wary of similar situations occurring in future for messages that we
> can't detect and divert in advance and so have a few questions:
> - What would be the recommended handling of this situation?
> - Is it possible to clear just these messages from the channel or does the
> whole channel have to be deleted ?
> - Is there a way that we can divert these messages to another channel
> (dead letter / invalid message style) ? Noting that they are not known to
> be problematic until after an attempt is made to deliver them from the sink
> - What happens to other messages in a batch with a bad message ? Will they
> also be stuck forever or will they be taken in another batch ?
> Thanks,
> Paul.
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