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From Noel Duffy <noel.du...@sli-systems.com>
Subject Architecting Flume for failover
Date Tue, 19 Feb 2013 21:32:36 GMT
I have a Flume agent that pulls events from RabbitMQ and pushes them into HDFS. So far so good,
but now I want to have a second Flume agent on a different host acting as a hot backup for
the first agent such that the loss of the first host running Flume would not cause any events
to be lost. In the testing I've done I've gotten two Flume agents on separate hosts to read
the same events from the RabbitMQ queue, but it's not clear to me how to configure the sinks
such that only one of the sinks actually does something and the other does nothing.

>From reading the documentation, I supposed that a sinkgroup configured for failover was
what I needed, but the documentation examples only cover the case where the sinks in a failover
group are all on the same agent on the same host. I've seen messages online which seem to
say that sinks in a sinkgroup can be on different hosts, but I can find no clear explanation
of how to configure such a sinkgroup. How would sinks on different hosts communicate with
one another? Would the sinks in the sinkgroup have to use a JDBC channel? Would the sinks
have to be non-terminal sinks, like Avro?

In my testing I set up two agents on different hosts and configured a sinkgroup containing
two sinks, both HDFS sinks.  

agent.sinkgroups = sinkgroup1
agent.sinkgroups.sinkgroup1.sinks = hdfsSink-1 hdfsSink-2
agent.sinkgroups.sinkgroup1.processor.priority.hdfsSink-1 = 5
agent.sinkgroups.sinkgroup1.processor.priority.hdfsSink-2 = 10
agent.sinkgroups.sinkgroup1.processor.type=failover

agent.sinks = hdfsSink-1 hdfsSink-2
agent.sinks.hdfsSink-1.type = hdfs
agent.sinks.hdfsSink-1.bind = 10.20.30.81
agent.sinks.hdfsSink-1.channel = fileChannel-1
agent.sinks.hdfsSink-1.hdfs.path = /flume/localbrain-events
agent.sinks.hdfsSink-1.hdfs.filePrefix = lb-events
agent.sinks.hdfsSink-1.hdfs.round = false
agent.sinks.hdfsSink-1.hdfs.rollCount=50
agent.sinks.hdfsSink-1.hdfs.fileType=SequenceFile
agent.sinks.hdfsSink-1.hdfs.writeFormat=Text
agent.sinks.hdfsSink-1.hdfs.codeC = lzo
agent.sinks.hdfsSink-1.hdfs.rollInterval=30
agent.sinks.hdfsSink-1.hdfs.rollSize=0
agent.sinks.hdfsSink-1.hdfs.batchSize=1

agent.sinks.hdfsSink-2.bind = 10.20.30.119
agent.sinks.hdfsSink-2.type = hdfs
agent.sinks.hdfsSink-2.channel = fileChannel-1
agent.sinks.hdfsSink-2.hdfs.path = /flume/localbrain-events
agent.sinks.hdfsSink-2.hdfs.filePrefix = lb-events
agent.sinks.hdfsSink-2.hdfs.round = false
agent.sinks.hdfsSink-2.hdfs.rollCount=50
agent.sinks.hdfsSink-2.hdfs.fileType=SequenceFile
agent.sinks.hdfsSink-2.hdfs.writeFormat=Text
agent.sinks.hdfsSink-2.hdfs.codeC = lzo
agent.sinks.hdfsSink-2.hdfs.rollInterval=30
agent.sinks.hdfsSink-2.hdfs.rollSize=0
agent.sinks.hdfsSink-2.hdfs.batchSize=1

However, this does not achieve the failover I hoped for. The sink hdfsSink-2 on both agents
writes the events to HDFS. The agents are not communicating, so the binding of the sink to
an ip address is not doing anything.



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