I'm currently deploying ganglia 3.1.0. I noticed that there were
problems with nodes appearing in the gmond xml feed with no metrics, or
with fewer metrics than they should have.
My network config is as follows:
udp_send_channel {
host = borgdev20
port = 8650
}
udp_recv_channel {
port = 8650
}
tcp_accept_channel {
port = 8181
}
It appears that when the gmond collecter, on borgdev20, receives a
metric for which it has no metadata, which may happen (for example) when
the collector has been restarted since the leaf nodes have been
collected, it sends out a request for metadata. This seems reasonable.
However, it sends it out to the udp_recv_channel, not to the host which
sent the metric. This, I think, would work with multicast configs, but
in the case of unicast, gmond sends the metadata request to itself, and
then throws it in the bitbucket when it receives it.
When I found this problem, I added send_metadata_interval = 15 to my
gmond.conf, and this seems to resolve the issue. It does so, however,
at the cost of much network traffic.
It is probably a good idea to do two things here:
1) make gmond request metadata from the host which sent the unknown
metric, if it is not running in multicast mode.
2) document that there is a new requirement for a working unicast
system: in version 3.0.5, IIRC, the only requirement for leaves is that
they be able to send packets to the collector. In version 3.1.0, the
collector must be able to get a packet back to it's leaf nodes, unless
the leaf nodes are sending periodic metadata.
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