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RE: Architecting Flume for failover
That makes sense. Thanks for the detailed reply. And thanks to Hari, Jeff, and everyone else who took time to answer.

From: Juhani Connolly [[EMAIL PROTECTED]]
Sent: Wednesday, 20 February 2013 7:27 p.m.
Subject: Re: Architecting Flume for failover

Sink-groups are a concept local to a single agent. What is happening to
you is both your agents have the same sink group, and they're both
selecting the highest priority sink.

Agents are independent and communicate with each other via sink-source
couplings such as avro-sink to avro-source(or thrift).

Fail-over and load balancing in sink groups is intended to be a
mechanism that redirects traffic when a particular sink fails. So if say
you have two hdfs clusters, and one fails, you can reroute your data to
the secondary one until it recovers.

If you want to failover agents,  what you likely want to do to
guarrantee immediate delivery is just set up two agents that are both
directing the data to your hdfs cluster. Then when processing the data
filter out duplicates.

If this isn't workable, more complex methods might involve adding
sequence numbers to the data, and another flume agent with an
interceptor that filters out duplicates based on the sequence numbers.
This would be rather complex, and isn't something built into flume.

On 02/20/2013 03:07 PM, Noel Duffy wrote:
> I think we're talking at cross purposes here. First, let me re-state the problem at a high level. Hopefully this will be clearer:
> I want to have two or more Flume agents running on different hosts reading events from the same source (RabbitMQ) but only writing the event to the final sink (hdfs) once. Thus, if someone kicks out a cable and one of the Flume hosts dies, the other(s) should take over seamlessly without the loss of any events. I thought that failover and load-balancer sinkgroups were created to solve this kind of problem, but the documentation only covers the case where all the sinks in the sinkgroup are on one host, and this does not give me the redundancy I need.
> This is how I tried to solve the problem. I set up two hosts running Flume with the same configuration. Thinking that a failover sinkgroup was the right approach to tackling my problem, I created a sinkgroup and put two hdfs sinks in it, hdfsSink-1 and hdfsSink-2. The idea was that hdfsSink-1 would be on Flume host A and hdfsSink-2 would be on Flume host B. Then, events arrive on both host A and host B, and host A would write the event to hdfsSink-2, sending it across the network to Flume Host B, while host B would write the same event to hdfsSink-2 which is local to it.  Both agents should, in theory, write the event to the same sink on Flume Host B. Yes, I know that this would still duplicates the events, but I figured I would worry about that later. However, this has not worked as I expected. Flume Host A does not pass anything to Flume Host B.
> I need to know if the approach I've adopted, sinkgroups and failover, can achieve the kind of multi-host redundancy I want. If they can, are there examples of such configurations that I can see? If they cannot, what kind of configuration would be suitable for what I want to achieve?
> From: Hari Shreedharan [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, 20 February 2013 5:39 p.m.
> Subject: Re: Architecting Flume for failover
> Also, as Jeff said, sink-2 has a higher priority (the absolute value of the priority being higher, that sink is picked up).
> --
> Hari Shreedharan
> On Tuesday, February 19, 2013 at 8:37 PM, Hari Shreedharan wrote:
> No, it does not mean that. To talk to different HDFS clusters you must specify the hdfs.path as hdfs://namenode:port/<path>. You don't need to specify the bind etc.
> Hope this helps.
> Hari
> --
> Hari Shreedharan
> On Tuesday, February 19, 2013 at 8:18 PM, Noel Duffy wrote:
> Hari Shreedharan [mailto:[EMAIL PROTECTED]] wrote: