README

An [ElasticSearch] availability and performance monitoring plugin for 
Nagios.

This plugin works by submitting API requests to a local or remote 
ElasticSearch server.  ElasticSearch servers will respond to these API 
requests by default.  If yours don't, check that you have not set 
`http.enabled` to `false`.

This plugin may be used to monitor ElasticSearch data and proxy nodes.  
It is important that you run one instance of this plugin for each data 
node in your ElasticSearch cluster.  Certain failure modes that can be 
localised to a particular data node will not be reported by unaffected 
data or proxy nodes.

ElasticSearch defines its [own thresholds][cluster-health] for 'green', 
'yellow', and 'red'.  Most other ElasticSearch monitoring plugins simply 
take this 'health colour' and map it directly to a Nagios check status 
(OK, WARNING, or CRITICAL, respectively).  While that approach will work 
(insofar as it will report a problem that ElasticSearch has detected), 
an operator is going to need more information to narrow a real problem 
down to its root cause.  ('*Why* is my cluster yellow?')

This monitoring plugin requests detailed operational data from 
ElasticSearch and uses that information to derive its own 'health 
colour'.  If our health colour concurs with ElasticSearch's health 
colour, then we can be reasonably sure we know what is wrong with the 
cluster and may report that problem to the operator.


[ElasticSearch]: http://www.elasticsearch.org/
[cluster-health]: http://www.elasticsearch.org/guide/reference/api/admin-cluster-health.html