The Nomad client can now optionally emit telemetry data from the
prerun and prestart hooks. This allows operators to monitor and
alert on failures and time taken to complete.
The new datapoints are:
- nomad.client.alloc_hook.prerun.success (counter)
- nomad.client.alloc_hook.prerun.failed (counter)
- nomad.client.alloc_hook.prerun.elapsed (sample)
- nomad.client.task_hook.prestart.success (counter)
- nomad.client.task_hook.prestart.failed (counter)
- nomad.client.task_hook.prestart.elapsed (sample)
The hook execution time is useful to Nomad engineering and will
help optimize code where possible and understand job specification
impacts on hook performance.
Currently only the PreRun and PreStart hooks have telemetry
enabled, so we limit the number of new metrics being produced.
This change adds configuration options for setting the in-memory
telemetry sink collection and retention durations. This sink backs
the metrics JSON API and previously had hard-coded default values.
The new options are particularly useful when running development or
debug environments, where metrics collection is desired at a fast
and granular rate.
Metrics tools that "pull" metrics, such as Prometheus, have a configurable
interval for how frequently they scrape metrics. This should be greater or equal
to the Nomad `telemetry.collection_interval` to avoid re-scraping metrics that
cannot have been updated in that interval.
Fixes: https://github.com/hashicorp/nomad/issues/20055
