OCPBUGS-84814: Skip chrony-wait on boot 2 when time was recently synced

[sdodson]

Summary

During node scale-up, chrony-wait.service blocks boot 2 for 8–14s on AWS (up to 24s on Azure) waiting for NTP synchronization. This wait is unnecessary when chronyd already synced time during boot 1 (MCD firstboot) and wrote the drift file on clean shutdown.

This PR adds a lightweight check that skips the blocking chrony-wait when the drift file proves time was recently synced:

• chrony-drift-check.service — runs after chronyd, before chrony-wait. Checks if /var/lib/chrony/drift was modified less than 60 minutes ago. If so, creates /run/chrony-recently-synced (tmpfs, auto-cleaned on reboot).
• Drop-in for chrony-wait.service — adds ConditionPathExists=!/run/chrony-recently-synced. When the flag exists, systemd skips the blocking wait entirely.

Why this approach

Why not modify chrony-wait's ExecStart directly?

chrony-wait.service runs in a strict systemd sandbox (ProtectSystem=strict, PrivateUsers=yes). A wrapper script replacing ExecStart runs under the unconfined_service_t SELinux context, which is denied access to /var/lib/chrony/drift (labeled chronyd_var_lib_t). The directory has 0750 chrony:chrony permissions, making it inaccessible even to root under the user namespace remapping.

Using a separate unsandboxed service avoids this entirely while leaving chrony-wait's security sandbox untouched.

Why not use ConditionPathExists on the drift file?

ConditionPathExists can only check existence, not file age. We need to distinguish between a drift file that was written minutes ago (safe to skip) and one that was written hours or days ago (machine was powered off, need fresh NTP sync).

Why is this safe?

• chronyd reliably writes the drift file on clean shutdown during boot 1. Verified across 250+ scale-up runs on AWS and Azure — 100% success rate.
• The drift file is read immediately at chronyd startup on boot 2 (within the same second), confirming it persists across the MCD reboot.
• The flag is in /run/ (tmpfs), so it is automatically cleaned on every reboot — no stale state accumulates.
• If the drift file is absent or stale (>1 hour), the check falls through and chrony-wait blocks normally.

Test results

Tested on AWS 4.20 with m6i.xlarge instances:

Before (baseline): chrony-wait blocks for 8–14s on boot 2

Starting Wait for chrony to synchronize system clock...
[8-14 seconds of chronyc waitsync retries]
Finished Wait for chrony to synchronize system clock.

After: chrony-wait skipped entirely

Starting Check if chrony drift file is recent...
chrony-drift-check: drift file age=24s
chrony-drift-check: created /run/chrony-recently-synced, chrony-wait will skip
Finished Check if chrony drift file is recent.
Wait for chrony to synchronize system clock was skipped because of an unmet condition check (ConditionPathExists=!/run/chrony-recently-synced).

Test plan

• Verify fresh node scale-up skips chrony-wait on boot 2
• Verify existing worker MCP rollout (reboot) skips chrony-wait
• Verify initial cluster install still blocks on chrony-wait (no drift file exists on first-ever boot)
• Verify node that was powered off for >1 hour blocks on chrony-wait (stale drift file)
• Verify chronyc tracking shows clock is synchronized after boot completes

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added automated chrony drift monitoring to detect recent time synchronization events
  • Implemented conditional service behavior that skips dependent services when synchronization is current

[openshift-merge-bot]

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[coderabbitai]

Walkthrough

A new chrony synchronization detection mechanism is introduced: a check script monitors drift file age and creates a marker when recently synced; a systemd service runs the script with proper ordering; a drop-in config skips chrony-wait if that marker exists.

Changes

Chrony Sync Detection

Layer / File(s)	Summary
Script Implementation templates/common/_base/files/chrony-drift-check.yaml	Bash script installed to /usr/local/bin/chrony-drift-check.sh checks if /var/lib/chrony/drift is less than 3600 seconds old; if so, creates /run/chrony-recently-synced marker and exits successfully.
Service Orchestration templates/common/_base/units/chrony-drift-check.service.yaml	Systemd oneshot service executes the drift-check script, ordered to run after chronyd.service and before chrony-wait.service, installed to multi-user.target.
Conditional Skip Integration templates/common/_base/units/chrony-wait.service.yaml	Drop-in config 10-skip-if-recently-synced.conf adds ConditionPathExists=!/run/chrony-recently-synced to skip chrony-wait.service when the marker file exists.

Sequence Diagram

sequenceDiagram
    actor System
    participant chronyd as chronyd.service
    participant check as chrony-drift-check.service
    participant script as drift-check.sh
    participant chrony_wait as chrony-wait.service

    System->>chronyd: Start
    activate chronyd
    chronyd->>check: (After chronyd starts)
    check->>script: Execute /usr/local/bin/chrony-drift-check.sh
    activate script
    script->>script: Check /var/lib/chrony/drift age
    alt Drift file < 3600 seconds old
        script->>script: Touch /run/chrony-recently-synced
    end
    script-->>check: Exit 0
    deactivate script
    check-->>System: Service complete (RemainAfterExit=yes)
    
    rect rgba(200, 150, 100, 0.5)
    Note over chrony_wait: Now ready to start<br/>(Before chrony-drift-check)
    end
    
    chrony_wait->>chrony_wait: Check ConditionPathExists=/run/chrony-recently-synced
    alt Marker exists
        chrony_wait-->>System: Skip execution
    else Marker absent
        chrony_wait->>chrony_wait: Run normally
    end

Loading

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 12

✅ Passed checks (12 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Stable And Deterministic Test Names	✅ Passed	Pull request contains only YAML template files for systemd services and scripts, with no Ginkgo test files or test definitions added.
Test Structure And Quality	✅ Passed	The PR contains only YAML template files and no Ginkgo test code, making the test quality custom check not applicable.
Microshift Test Compatibility	✅ Passed	This pull request does not add any Ginkgo e2e tests. The changes consist entirely of three YAML template files for systemd services related to chrony time synchronization, not test definitions.
Single Node Openshift (Sno) Test Compatibility	✅ Passed	PR adds systemd service unit templates and shell scripts for chrony synchronization, not Ginkgo e2e tests. SNO compatibility check does not apply.
Topology-Aware Scheduling Compatibility	✅ Passed	Pull request adds systemd service unit templates and bash script for chrony drift checking. These are host-level systemd service definitions with no Kubernetes scheduling constructs, pod affinity rules, node selectors, or topology-dependent logic.
Ote Binary Stdout Contract	✅ Passed	The OTE Binary Stdout Contract check is not applicable to this PR. The PR exclusively adds three YAML template files and an embedded Bash script for chrony drift file checks. No Go source code was modified, and the shell script does not write to stdout.
Ipv6 And Disconnected Network Test Compatibility	✅ Passed	PR adds YAML templates and bash script only; no Ginkgo e2e tests with IPv4 assumptions or external connectivity requirements are introduced.
Title check	✅ Passed	The title accurately reflects the main changes: introducing a mechanism to skip chrony-wait.service when time was recently synced, which is the core objective of the PR.

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[openshift-ci]

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[sdodson]

/test e2e-aws-ovn

[openshift-ci]

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[openshift-ci-robot]

@sdodson: This pull request references Jira Issue OCPBUGS-84814, which is valid. The bug has been moved to the POST state.

3 validation(s) were run on this bug

• bug is open, matching expected state (open)
• bug target version (5.0.0) matches configured target version for branch (5.0.0)
• bug is in the state New, which is one of the valid states (NEW, ASSIGNED, POST)

The bug has been updated to refer to the pull request using the external bug tracker.

Details

In response to this:

Summary

During node scale-up, chrony-wait.service blocks boot 2 for 8–14s on AWS (up to 24s on Azure) waiting for NTP synchronization. This wait is unnecessary when chronyd already synced time during boot 1 (MCD firstboot) and wrote the drift file on clean shutdown.

This PR adds a lightweight check that skips the blocking chrony-wait when the drift file proves time was recently synced:

• chrony-drift-check.service — runs after chronyd, before chrony-wait. Checks if /var/lib/chrony/drift was modified less than 60 minutes ago. If so, creates /run/chrony-recently-synced (tmpfs, auto-cleaned on reboot).
• Drop-in for chrony-wait.service — adds ConditionPathExists=!/run/chrony-recently-synced. When the flag exists, systemd skips the blocking wait entirely.

Why this approach

Why not modify chrony-wait's ExecStart directly?

chrony-wait.service runs in a strict systemd sandbox (ProtectSystem=strict, PrivateUsers=yes). A wrapper script replacing ExecStart runs under the unconfined_service_t SELinux context, which is denied access to /var/lib/chrony/drift (labeled chronyd_var_lib_t). The directory has 0750 chrony:chrony permissions, making it inaccessible even to root under the user namespace remapping.

Using a separate unsandboxed service avoids this entirely while leaving chrony-wait's security sandbox untouched.

Why not use ConditionPathExists on the drift file?

ConditionPathExists can only check existence, not file age. We need to distinguish between a drift file that was written minutes ago (safe to skip) and one that was written hours or days ago (machine was powered off, need fresh NTP sync).

Why is this safe?

• chronyd reliably writes the drift file on clean shutdown during boot 1. Verified across 250+ scale-up runs on AWS and Azure — 100% success rate.
• The drift file is read immediately at chronyd startup on boot 2 (within the same second), confirming it persists across the MCD reboot.
• The flag is in /run/ (tmpfs), so it is automatically cleaned on every reboot — no stale state accumulates.
• If the drift file is absent or stale (>1 hour), the check falls through and chrony-wait blocks normally.

Test results

Tested on AWS 4.20 with m6i.xlarge instances:

Before (baseline): chrony-wait blocks for 8–14s on boot 2

Starting Wait for chrony to synchronize system clock...
[8-14 seconds of chronyc waitsync retries]
Finished Wait for chrony to synchronize system clock.

After: chrony-wait skipped entirely

Starting Check if chrony drift file is recent...
chrony-drift-check: drift file age=24s
chrony-drift-check: created /run/chrony-recently-synced, chrony-wait will skip
Finished Check if chrony drift file is recent.
Wait for chrony to synchronize system clock was skipped because of an unmet condition check (ConditionPathExists=!/run/chrony-recently-synced).

Test plan

• Verify fresh node scale-up skips chrony-wait on boot 2
• Verify existing worker MCP rollout (reboot) skips chrony-wait
• Verify initial cluster install still blocks on chrony-wait (no drift file exists on first-ever boot)
• Verify node that was powered off for >1 hour blocks on chrony-wait (stale drift file)
• Verify chronyc tracking shows clock is synchronized after boot completes

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
• Added automated chrony drift monitoring to detect recent time synchronization events
• Implemented conditional service behavior that skips dependent services when synchronization is current

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