Document node_exporter collector customization and limitations

[Copilot]

PMM-0

Link to the Feature Build: SUBMODULES-0

Description

Users need to customize node_exporter collectors (enable mdadm, configure netdev.address-info) but documentation is missing. Investigation revealed PMM only supports disabling collectors via --disable-collectors flag, not enabling disabled ones.

Changes

Investigation artifacts (this repo):

• NODE_EXPORTER_CUSTOMIZATION_FINDINGS.md - Technical analysis of node_exporter config in managed/services/agents/node.go, API (api/inventory/v1/agents.proto), and CLI (admin/commands/config.go)
• NODE_EXPORTER_DOCUMENTATION_README.md - User-facing summary with quick answers
• create-documentation-pr.sh - Helper script for pmm-doc PR creation
• 0001-Document-node_exporter-collector-customization-v2.patch - Documentation changes for pmm-doc repo

Documentation created (pmm-doc repo at /tmp/pmm-doc):

• Enhanced docs/how-to/extend-metrics.md (+178 lines):
  • Lists 30+ enabled collectors (cpu, diskstats, meminfo, netdev, etc.)
  • Lists 26+ disabled collectors (mdadm, systemd, ntp, etc.)
  • Documents --disable-collectors flag usage
  • Provides textfile collector workaround for disabled collectors
  • Includes validated bash script for mdadm metrics collection
• Updated docs/details/commands/pmm-admin.md (+3 lines):
  • Added --disable-collectors flag to pmm-admin config reference

Key findings:

• --no-collector.mdadm is hardcoded in managed/services/agents/node.go:91
• No enable_collectors API parameter exists
• No mechanism for collector-specific flags like --collector.netdev.address-info
• Configuration immutable after initial setup

Example usage:

# Supported: disable collectors during setup
pmm-admin config \
    --disable-collectors=netdev,netstat,vmstat \
    192.168.1.10 generic node1

# Not supported: enabling disabled collectors
# Workaround: use textfile collector (see documentation)

Branch document-node-exporter-customization in /tmp/pmm-doc ready for PR to percona/pmm-doc.

If this PR adds, removes or alters one or more API endpoints, please review and add or update the relevant API documentation as well:

• API Docs updated (N/A - documentation only)

If this PR is related to some other PRs in this or repositories, please provide links to those PRs:

• Documentation PR to be created in percona/pmm-doc from artifacts in this PR

Original prompt

Investigate PMM node_exporter Configuration and Create Documentation PR

Context

A user needs to customize node_exporter startup arguments in PMM (Percona Monitoring and Management), specifically to:

• Remove the --no-collector.mdadm flag (currently disabled by default)
• Enable the netdev.address-info collector

The current PMM 3 documentation at https://docs.percona.com/percona-monitoring-and-management/3/ does not explain how to customize node_exporter arguments.

Task

Please perform the following:

1. Code Investigation

   • Examine the PMM codebase (https://github.com/percona/pmm) to determine:
     • Where and how pmm-agent starts node_exporter
     • Which node_exporter collectors are enabled/disabled by default
     • Whether there's a supported mechanism to customize node_exporter startup arguments
     • If configuration files or environment variables can control collector behavior
   • Check both pmm-agent and pmm-admin code for relevant configuration options

2. Documentation Analysis

   • Review the existing documentation structure at https://github.com/percona/pmm-doc
   • Identify the appropriate location for node_exporter customization documentation
   • Determine if this should be:
     • A new topic under "Extend metrics"
     • An addition to the pmm-agent command reference
     • A troubleshooting/FAQ entry

3. Create Pull Request
   If customization is possible, create a PR to the pmm-doc repository that:

   • Explains how to customize node_exporter startup arguments
   • Provides specific examples for enabling/disabling collectors
   • Documents any configuration file changes needed
   • Includes warnings about manual modifications if applicable
   • Shows how to verify the changes took effect

   If customization is NOT currently possible, create a PR that:

   • Documents this limitation clearly
   • Explains the textfile collector workaround as an alternative
   • References the relevant feature request or issue
   • Suggests users open a feature request in PMM JIRA

4. Deliverables

   • Summary of findings from code investigation
   • Link to the documentation PR
   • Example commands/configuration for the specific use case (mdadm and netdev.address-info collectors)

Target Documentation Format

Follow PMM documentation standards:

• Use MkDocs markdown format
• Include code examples with proper syntax highlighting
• Add appropriate admonitions (Note, Warning, etc.)
• Link to related documentation pages
• Follow the existing documentation style and structure

Priority

This is a common use case for system administrators who need to monitor specific hardware or network metrics that are disabled by default in node_exporter.

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