ReadonlyFilesystem Condition with Auto-Recovery Detection

[CharudathGopal]

ISSUE: #474

Problem Statement
The existing NPD SystemLogMonitor for ReadonlyFilesystem is a one-way trigger: it sets the condition to True when detecting Remounting filesystem read-only in kernel logs, but never clears it. The condition remains stuck until NPD pod restart or node reboot, causing some Kubernetes platform to delete the node.

Solution: CustomPluginMonitor with Active Recovery Detection

This PR introduces a CustomPluginMonitor (check_ro_filesystem.sh) that actively monitors both detection and recovery of read-only filesystems.

Key Features

1. NPD Design Adherence & Detection (5-minute lookback)

   • Mimics NPD's SystemLogMonitor by scanning /dev/kmsg for "Remounting filesystem read-only" messages
   • Uses 5-minute lookback window (300 seconds) calculated from /proc/uptime
   • Filters kernel messages by timestamp to match NPD's behavior
   • Extracts device names from kernel messages (e.g., pxd!pxd208624217308167071, dm-3, sda1)
   • Checks if extracted devices are currently mounted read-only in /host/proc/1/mounts
   • If any device is RO: Exit 1 → Condition = True

2. Recovery Check (all-time lookback)

   • If no recent errors found, performs second scan of /dev/kmsg with no time limit
   • Retrieves ALL historical "remounting filesystem read-only" messages since boot
   • Checks if ANY historically-problematic devices are still mounted read-only
   • If all devices recovered or unmounted: Exit 0 → Condition = False
   • Enables automatic recovery detection - the key differentiator from SystemLogMonitor

3. Targeted Approach (Avoids False Positives)

   • Only monitors devices that kernel explicitly reported as having errors
   • Does NOT scan all mounts in /proc/mounts (which would flag legitimate read-only mounts like /boot, CD-ROMs, ConfigMaps)
   • More accurate and simpler than filesystem-wide scanning
   • Prevents false positives from intentionally read-only filesystems

Deployment Changes

ReadonlyFilesystem CustomPluginMonitor is not enabled by default, users can enable this feature by following steps documented in docs/readonly-recovery-plugin-monitor.md

• Adds /host/proc volume mount to access host mount table
• Replace --config.system-log-monitor=/config/readonly-monitor.json with --config.custom-plugin-monitor=/config/readonly-recovery-plugin-monitor.json

[k8s-ci-robot]

Welcome @CharudathGopal!

It looks like this is your first PR to kubernetes/node-problem-detector 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes/node-problem-detector has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

Hi @CharudathGopal. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: CharudathGopal
Once this PR has been reviewed and has the lgtm label, please assign sjenning for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment