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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10181) GangliaContext does not work with multicast ganglia setup
Date Wed, 11 Feb 2015 07:32:11 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14315720#comment-14315720

Todd Lipcon commented on HADOOP-10181:

Sorry for the late reply, I was on vacation the last few weeks. The patch looks fine to me.
Thanks for reviewing and committing, Chris.

> 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
>          Components: metrics
>    Affects Versions: 2.6.0
>            Reporter: Andrew Otto
>            Assignee: Andrew Johnson
>            Priority: Minor
>              Labels: ganglia, hadoop, metrics, multicast
>             Fix For: 2.7.0
>         Attachments: HADOOP-10181.001.patch, HADOOP-10181.002.patch, HADOOP-10181.003.patch
> 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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