Andrew Otto created HADOOP-10181:
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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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