[collectd] Problems with the curl_json plugin an ElasticSearch 'node stats' info?

[Matt Wise]

In our environment, we're using Collectd 4.10.1 (I know ... old as dirt,
but its a requirement of RightScale) and we are trying to leverage the
curl_json plugin to pull metrics from our ElasticSearch cluster. We have
the metrics coming in properly from http://localhost:9200/_cluster/stats
and http://localhost:9200/_cluster/health.

What we can't get working though are *any* metrics from
http://localhost:9200/_nodes/_local/stats. No matter how many or few
metrics I define, and no matter whether I use 'nodes/*/...' or
'nodes/<insert node id here>/...', I cannot seem to get any data from this
endpoint.

Here is our entire collectd elasticsearch.conf file, and a real copy of the
raw node stats json output:
  https://gist.github.com/diranged/ac7d2edb45b0eba00d42

Any ideas on what might be going on? I can't seem to get any debug logs
either, and unfortunately the collectd-dbg package for 4.10.1 is not
available it seems like, so we're really hamstrung here.

I have verified that ..
  .. Collectd is indeed making the curl call to ElasticSearch and the
response is coming back properly (via strace, and tcpdump)
 .. Replacing '*' with 'HYUqTMnfSgmvd87_o3UPLw' (the node id) in the config
file does not help
 .. Dropping all the way down to a single metric
(jvm/mem/heap_used_in_bytes) does not help

Can anyone help here?

Matt Wise
Sr. Systems Architect
Nextdoor.com
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