in_node_exporter_metrics: add new option 'path.rootfs'

[edsiper]

This PR fixes #10650

This PR introduces a new path.rootfs configuration parameter to the node_exporter_metrics input plugin, simplifying containerized deployments by allowing users to specify a single root filesystem mount point instead of mounting /proc and /sys separately.

Changes Made

Plugin Configuration:

• Added path.rootfs config option with default value /
• When path.rootfs is set to a non-root path, the plugin automatically composes full paths for:

e.g:

• path.procfs → {rootfs}/proc
• path.sysfs → {rootfs}/sys
• path.textfile → {rootfs}/{textfile_path} (if specified)

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• New Features
  • Added a rootfs path configuration for Node Exporter Metrics, automatically prefixing procfs/sysfs/textfile paths to simplify containerized setups.
• Documentation
  • Added comments guiding how to use host root paths when running in containers.
• Chores
  • Updated the node-exporter dashboard container to mount the host root as read-only and use the new rootfs configuration, reducing multiple bind mounts to a single one.
• Bug Fixes
  • Improved error logging when reading system stats fails, aiding troubleshooting.

[coderabbitai]

Walkthrough

Introduces path.rootfs support to the in_node_exporter_metrics plugin, adds rootfs-based path composition for procfs/sysfs/textfile, updates docker-compose to use path.rootfs with a host root mount, adds a minor error log, and inserts non-functional comments and formatting changes.

Changes

Cohort / File(s)	Summary
Config comments conf/fluent-bit-metrics.conf	Added two comments explaining host root path usage; no runtime effect.
Docker compose update docker_compose/node-exporter-dashboard/docker-compose.yml	Switched Fluent Bit args from path.procfs/path.sysfs to path.rootfs; changed mounts from /proc and /sys to read-only host root (/:/host:ro).
Plugin config map: path.rootfs plugins/in_node_exporter_metrics/ne.c	Added config_map entry for path.rootfs (string, default “/”) mapped to flb_ne.path_rootfs.
Plugin context struct plugins/in_node_exporter_metrics/ne.h	Added flb_sds_t path_rootfs to struct flb_ne.
Rootfs path composition logic plugins/in_node_exporter_metrics/ne_config.c	On init, prefixes procfs/sysfs/textfile paths with path.rootfs (handling trailing slash); logs selected paths.
Linux stat logging plugins/in_node_exporter_metrics/ne_stat_linux.c	Added error log when reading procfs stat fails.
Formatting only plugins/in_node_exporter_metrics/ne_utils.c, plugins/in_node_exporter_metrics/ne_utils.h	Reflowed function declaration formatting; no functional changes.

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant FluentBit
    participant in_node_exporter_metrics
    participant HostFS

    User->>FluentBit: Configure path.rootfs=/host
    FluentBit->>in_node_exporter_metrics: Initialize plugin
    in_node_exporter_metrics->>in_node_exporter_metrics: Compose procfs/sysfs/textfile paths with path.rootfs
    in_node_exporter_metrics->>HostFS: Read /host/proc, /host/sys, textfiles
    HostFS-->>in_node_exporter_metrics: Metrics data
    in_node_exporter_metrics-->>FluentBit: Emit metrics

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~15 minutes

Assessment against linked issues

Objective	Addressed	Explanation
Add path.rootfs configuration to in_node_exporter_metrics (#10650)	✅
Use path.rootfs to prefix filesystem access for metrics collection (#10650)	✅

Possibly related PRs

• in_node_exporter_metrics: add Linux sockstat collector #10718 — Modifies in_node_exporter_metrics configuration and struct fields, overlapping with this PR’s additions.

Suggested labels

docs-required

Suggested reviewers

• leonardo-albertovich
• koleini
• fujimotos

Poem

I hop through roots where syscalls grow,
A burrow mapped to /host below.
With whiskered logs and paths anew,
I sniff out metrics, crisp and true.
One leap, proc sings; two hops, sys gleams—
Rootfs aligned, we harvest streams. 🐇📊

---

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📥 Commits

Reviewing files that changed from the base of the PR and between e7aba68 and f2e24ca.

📒 Files selected for processing (8)

• conf/fluent-bit-metrics.conf (1 hunks)
• docker_compose/node-exporter-dashboard/docker-compose.yml (1 hunks)
• plugins/in_node_exporter_metrics/ne.c (1 hunks)
• plugins/in_node_exporter_metrics/ne.h (1 hunks)
• plugins/in_node_exporter_metrics/ne_config.c (2 hunks)
• plugins/in_node_exporter_metrics/ne_stat_linux.c (1 hunks)
• plugins/in_node_exporter_metrics/ne_utils.c (1 hunks)
• plugins/in_node_exporter_metrics/ne_utils.h (1 hunks)

🧰 Additional context used

🧬 Code Graph Analysis (1)

plugins/in_node_exporter_metrics/ne_config.c (1)

src/flb_sds.c (2)

• flb_sds_create_size (92-95)
• flb_sds_printf (336-387)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (22)

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🔇 Additional comments (8)

plugins/in_node_exporter_metrics/ne_utils.h (1)

38-39: LGTM! Formatting improvement.

The parameter line-wrapping improves readability without changing the function signature.

plugins/in_node_exporter_metrics/ne_utils.c (1)

199-201: LGTM! Consistent formatting.

The parameter formatting is now consistent with the header file and improves readability.

plugins/in_node_exporter_metrics/ne_stat_linux.c (1)

88-88: Good improvement for debugging.

Adding error logging when stat file reading fails will help with troubleshooting, especially now that path_procfs can be dynamically composed with rootfs prefix.

conf/fluent-bit-metrics.conf (1)

18-19: Helpful documentation addition.

These comments provide clear guidance on using the new path.rootfs feature for containerized deployments.

plugins/in_node_exporter_metrics/ne.h (1)

51-51: Well-structured field addition.

The path_rootfs field is appropriately typed and positioned within the configuration section of the struct.

plugins/in_node_exporter_metrics/ne.c (1)

436-440: Well-implemented configuration option.

The path.rootfs configuration entry follows established patterns with appropriate default value and clear description.

docker_compose/node-exporter-dashboard/docker-compose.yml (2)

7-7: Correct configuration for rootfs usage.

The command properly demonstrates the new rootfs functionality by using a single path.rootfs parameter instead of separate procfs/sysfs parameters.

---

13-13: Good security practice with simplified mount.

The single host root mount with read-only flag simplifies the configuration while maintaining security. This aligns perfectly with the new rootfs feature.

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• Create PR with unit tests
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• Commit unit tests in branch in_node_exporter_metrics-rootfs

---

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