[stondo]

Summary

in_node_exporter_metrics refreshes each collector's values during init, but it only appends them to the pipeline when the scrape_interval timer fires (cb_ne_collect). With a long interval nothing is published until a full interval after startup: at scrape_interval: 3600 a host reports no metrics during the first hour after every boot or restart, and a host that restarts more often than the interval never reports at all.

Change

Add scrape_on_start, with the same pattern and wording as in_fluentbit_metrics: when enabled, and scrape_interval is greater than 5, a one-shot collector fires 5 seconds after startup, pauses itself and appends the current metrics. The regular interval collector is unchanged.

in_ne_pause and in_ne_resume also pause and resume the start collector, so it respects backpressure. Its id is cleared once it has fired, so a later resume does not re-arm it.

The option defaults to false, so existing configurations behave as before.

Example configuration

pipeline:
  inputs:
    - name: node_exporter_metrics
      scrape_interval: 3600
      scrape_on_start: true
  outputs:
    - name: prometheus_exporter
      match: "*"
      port: 2021

With the same setup on the command line (metrics=cpu,meminfo), curl localhost:2021/metrics returned 361 node_ series 8 seconds after startup with scrape_on_start=on, and none with it off.

Testing

• Two runtime tests in tests/runtime/in_node_exporter_metrics.c, both with scrape_interval: 3600 so only the start collector can produce output in time: with the option on a record reaches the output within 8 seconds, with it off none does. With the start collector disabled but the option still parsed, the first test fails.
• flb-rt-in_node_exporter_metrics: all 4 tests pass, and the two new ones run clean under valgrind.

Documentation

fluent/fluent-bit-docs#2794

Summary by CodeRabbit

• New Features
  • Added the scrape_on_start option for Node Exporter Metrics. When enabled, an initial metrics collection runs about five seconds after startup if the configured scrape interval is greater than five seconds. The option is disabled by default.

[chatgpt-codex-connector]

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📝 Code Review	✅ Completed 2026-10-22T15:50:43.058018Z	72f2dc0	PR opened

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• plugins/in_node_exporter_metrics/ne.c

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📝 Walkthrough

The Node Exporter Metrics input adds the scrape_on_start option, which defaults to false. When enabled and scrape_interval exceeds 5, it schedules an initial collection after five seconds. Runtime tests check output when the option is on and off.

Changes: Initial scrape

Layer / File(s)	Summary
Configure and run the initial scrape plugins/in_node_exporter_metrics/ne.h, plugins/in_node_exporter_metrics/ne.c, tests/runtime/in_node_exporter_metrics.c	Adds the scrape_on_start setting and state for the one-shot collector. When the option is enabled and scrape_interval exceeds 5, the input schedules an initial collection after five seconds. The callback pauses the one-shot collector, clears its descriptor, and runs regular collection. Linux runtime tests check output for enabled and disabled settings.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Input as Node Exporter Metrics input
  participant Scheduler as Fluent Bit collector scheduler
  participant StartCallback as cb_ne_collect_start
  participant CollectCallback as regular collection callback
  Input->>Scheduler: Schedule one-shot callback after five seconds
  Scheduler->>StartCallback: Invoke scheduled callback
  StartCallback->>Scheduler: Pause one-shot collector
  StartCallback->>CollectCallback: Run regular metrics collection

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Merge Risk: ⚪ Minimal · up to 06d7f

No actionable merge-blocking risk remains from the reviewed changes.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 22.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title "in_node_exporter_metrics: add scrape_on_start option" names the plugin and the new option that the changeset adds. The raw summary shows the option added to ne.c and ne.h, with a startup on…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title "in_node_exporter_metrics: add scrape_on_start option" names the plugin and the new option that the changeset adds. The raw summary shows the option added to ne.c and ne.h, with a startup one-shot collector that runs when scrape_on_start is enabled and scrape_interval is greater than 5. The PR objectives describe the same feature. The title is concise, specific, and matches the main change. It is 52 characters, which is within a normal title length.

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[chatgpt-codex-connector]

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Reviewed commit: 72f2dc0c14

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @plugins/in_node_exporter_metrics/ne.c:
- Line 266: Update the scrape_interval threshold in the start-collector
condition to use a strict greater-than-five-seconds check, preserving the
existing ctx->scrape_on_start requirement.

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[cosmo0920]

The changes are fine. Just waiting for the CI results.

[stondo]

Thanks. I raised the guard to scrape_interval > 5, so the start collector is only armed when it fires before the first regular round, and squashed it into the plugin commit. The docs row in fluent/fluent-bit-docs#2794 now states the limit.

[stondo]

Rebased onto master. The previous CIFuzz failure was an out-of-memory in cmetrics' unpack_meta_buckets(), already fixed by fluent/cmetrics@c132627 and brought in with #12641, which merged after that run.