aruraghuwanshi opened a new pull request, #19114:
URL: https://github.com/apache/druid/pull/19114
Add supervisor/count metric for health and state monitoring
Previously, supervisor health was only exposed via the REST API (`GET
/druid/indexer/v1/supervisor/{id}/health`) and the `sys.supervisors` SQL table.
There was no way to scrape supervisor health/state from Prometheus, StatsD, or
other metric emitters for monitoring and alerting.
This PR adds `SupervisorStatsMonitor`, which emits a `supervisor/count`
gauge metric per supervisor. Each active supervisor contributes a value of 1,
tagged with `supervisorId`, `type`, and `state` (RUNNING, SUSPENDED,
UNHEALTHY_SUPERVISOR, UNHEALTHY_TASKS, etc.). Users can aggregate by state for
dashboards and alerts (e.g. `sum(supervisor_count{state=~"UNHEALTHY_.*"})`).
### Description
#### Design
- **Pattern:** Mirrors `TaskCountStatsMonitor` / `TaskCountStatsProvider`: a
provider interface in `server/`, implemented by `SupervisorManager` in
`indexing-service/`, consumed by an Overlord-only monitor.
- **Metric:** `supervisor/count` — gauge, value 1 per supervisor;
dimensions: `supervisorId`, `type`, `state`.
- **State source:** Uses `getState().getBasicState()` (7 values) instead of
detailed states to avoid high cardinality.
- **Opt-in:** Users add `SupervisorStatsMonitor` to
`druid.monitoring.monitors`; no behavioral change without it.
- **Cost:** Only uses `getState()` and spec metadata (cheap reads); no
`getStatus()` calls on the monitor interval.
#### Release note
Adds a new `supervisor/count` metric when `SupervisorStatsMonitor` is
enabled in `druid.monitoring.monitors`. The metric reports each supervisor’s
state (RUNNING, SUSPENDED, UNHEALTHY_SUPERVISOR, etc.) for Prometheus, StatsD,
and other metric systems.
<hr>
##### Key changed/added classes in this PR
* `SupervisorStatsProvider` (new interface)
* `SupervisorStatsProvider.SupervisorStats` (new inner class)
* `SupervisorStatsMonitor` (new)
* `SupervisorManager` (implements `SupervisorStatsProvider`)
<hr>
This PR has:
- [x] been self-reviewed.
- [x] added documentation for new or modified features or behaviors.
- [x] a release note entry in the PR description.
- [x] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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