Add InfluxDB exporter to Actuator

[jmkgreen]

I am being pointed at InfluxDB by various people to record statistics, it would seem sensible to provide a MetricsWriter implementation for InfluxDB.

The InfluxDB side of things seems very well documented by them. Feels like this should be easy enough...

[philwebb]

It would indeed be a nice addition but I'm not sure if we'll get to it for 1.4 without some help. I've tagged as ideal-for-contribution, let's see if anyone can contribute something.

[jmkgreen]

https://github.com/jmkgreen/spring-boot-actuator-influxdb is the raw code - copied almost verbatim from the OpenTSDB writer.

Interestingly for InfluxDB it has both tags and fields. So where Metric is essentially a String identifier and a Long value, Influx asks that the value be associated with a field name. This is on top of any tags that might be included.

To start with the value is written to a field named simply value. I am unsure whether the existing metrics code base has enough semantics to map into field=value pairs or not..?

[dsyer]

See also #5701

[jmkgreen]

The code has been updated. I now have a demo application that is successfully writing into InfluxDB.

[dsyer]

@jmkgreen how does influxdb deal with counters? I only see a GaugeWriter in your implementation. It's not necessarily an issue, but I'm interested to know how you aggregate your counters across processes.

[jmkgreen]

If your question is "does influx accept a relative value" in order to increment a counter by some amount, it doesn't. It just records field=value pairs against a named metric. The line protocol takes a little getting used to due to metric names, fields, and tags. But it's the field values that rule out counters at the InfluxDB level.

Influx does have derivative() in the query interface. I would suggest posting gauges in with a suitable tag value of the current process id for consumers to spot changes over time of individual processes.

Looks like there are examples where metric names are checked for timer or gauge and considered to be a gauge, versus counter as a actual counter? There may be options here for interpretation.