Max ttl for gauges in statsd input plugin

[davidfaulkner12]

Feature Request

Proposal:

Allow for setting "gaugesMaxTTL" option in the statsd input plugin. Essentially, this from the core statsd repo:

https://github.com/statsd/statsd/pull/599/files

Current behavior:

If deleteGauges is set to "False" then once a gauge metric is reported it is reported for the life of the telegraf server. There is no way to set a TTL value where if the gauge metric is not received at the ingress endpoint after a certain time it is reset to 0.

Desired behavior:

An optional gaugesMaxTTL option is available for the statsd input -- this has exactly the same effect as the deleteGauges option, except that it only executes that logic after no input has been received for the value specified in gaugesMaxTTL.

Use case:

Telegraf server A on host X is taking input from service B and service C. Both of these services are reporting metrics via a gauge with "deleteGauges" set to False -- let's assume this is required w/o getting distracted by details. :-)

Now, service C is turned down by some load-managing automation. However, telegraf A will still report the last gauge metrics to Influx until restarted, with no way of ever reflecting the fact that service C is permanently gone.

[ssoroka]

This sounds like a great addition