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From "Andrew Otto (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-10181) GangliaContext does not work with multicast ganglia setup
Date Tue, 24 Dec 2013 18:44:50 GMT
Andrew Otto created HADOOP-10181:

             Summary: GangliaContext does not work with multicast ganglia setup
                 Key: HADOOP-10181
                 URL: https://issues.apache.org/jira/browse/HADOOP-10181
             Project: Hadoop Common
          Issue Type: Bug
            Reporter: Andrew Otto
            Priority: Minor

The GangliaContext class which is used to send Hadoop metrics to Ganglia uses a DatagramSocket
to send these metrics.  This works fine for Ganglia multicast setups that are all on the same
VLAN.  However, when working with multiple VLANs, a packet sent via DatagramSocket to a multicast
address will end up with a TTL of 1.  Multicast TTL indicates the number of network hops for
which a particular multicast packet is valid.  The packets sent by GangliaContext do not make
it to ganglia aggregrators on the same multicast group, but in different VLANs.

To fix, we'd need a configuration property that specifies that multicast is to be used, and
another that allows setting of the multicast packet TTL.  With these set, we could then use
MulticastSocket setTimeToLive() instead of just plain ol' DatagramSocket.

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