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Jenkins Upgrade Triage Guide

Problem: After upgrading Jenkins from 2.214 → 2.492.1, GitLab integration is broken (webhooks fail, merge request builds don’t trigger, pipeline steps like updateGitlabCommitStatus throw errors, etc.)

Root Cause (most common):
The GitLab Plugin and its dependency Jackson 2 API Plugin are incompatible with the newer libraries shipped in Jenkins 2.492.1 (Jackson 2.17+, Jetty 12, updated BOM).

Verified Working Combination for Jenkins 2.492.1 (LTS)

Plugin	Required Version	Release Date	Download / Plugin ID	Notes
GitLab Plugin	1.9.9	2025-09-06	gitlab-plugin	Latest stable, supports Jenkins ≥ 2.492.3
Jackson 2 API Plugin	2.20.0+	2025-xx-xx	jackson2-api	Provides Jackson Databind 2.17–2.19
(Optional) Jersey 2 API	2.39 or higher	—	jersey2-api	Usually auto-updated

Step-by-Step Fix (Triage Checklist)

1. Backup Current State
   • Export Configuration as Code (if using CasC)
   • Take a snapshot/backup of $JENKINS_HOME
2. Update Plugins (Recommended Order)
   • Manage Jenkins → Plugins → Installed
   • Or go directly to Updates tab
   • Install/Update:
     1. Jackson 2 API Plugin → 2.20.0 (or latest 2.20.x)
     2. GitLab Plugin → 1.9.9
   • Restart Jenkins when prompted
3. If Plugin Manager Shows Compatibility Warnings
   • Download the .hpi files manually:
     • GitLab Plugin 1.9.9: https://updates.jenkins.io/download/plugins/gitlab-plugin/1.9.9/gitlab-plugin.hpi
     • Jackson 2 API 2.20.0: https://updates.jenkins.io/download/plugins/jackson2-api/2.20.0/jackson2-api.hpi
   • Manage Jenkins → Plugins → Advanced → Upload Plugin

professionalism - Upload and restart

1. Verify Installation
   • Manage Jenkins → System Information
   • Search for:
     • gitlab-plugin version → 1.9.9
     • jackson2-api version → 2.20.0+
     • com.fasterxml.jackson.databind → 2.17.x–2.19.x
2. Test the Integration
   • Push a commit or open a merge request in GitLab
   • Check Jenkins job is triggered
   • Verify commit status appears in GitLab MR (pending → running → success/failure)
3. Enable Detailed Logging (if still failing)
   • Manage Jenkins → System Log → New Log Recorder
   • Name: GitLab Debug
   • Loggers (FINEST level):
     • com.dabsquared.gitlabjenkins
     • org.jenkinsci.plugins.gitlab
   • Reproduce the issue → copy stack trace

Common Errors & Quick Fixes

Symptom	Likely Cause	Fix
NoSuchMethodError / ClassNotFoundException involving Jackson classes	Old Jackson 2 API plugin	Force update to 2.20.0+
Webhook 500 error from Jenkins	GitLab plugin too old for Jetty 12	Upgrade to GitLab Plugin 1.9.9
updateGitlabCommitStatus step fails	State name changed in newer plugin	Use explicit states: pending, running, success, failed
401 Unauthorized on webhook	Secret token mismatch after upgrade	Re-save the GitLab connection in Global Tool Configuration
Builds not triggered at all	Webhook URL changed or blocked	Re-add webhook in GitLab (use new Jenkins URL if behind reverse proxy)

Rollback Plan (if needed)

• Downgrade only the two plugins back to versions known to work with your old setup (not recommended long-term).
• Never downgrade Jenkins core from 2.492.1 → 2.214 (security risk).

References

• GitLab Plugin: https://plugins.jenkins.io/gitlab-plugin/
• Jackson 2 API Plugin: https://plugins.jenkins.io/jackson2-api/
• Changelog 1.9.9: https://github.com/jenkinsci/gitlab-plugin/releases/tag/gitlab-plugin-1.9.9

Done. With GitLab Plugin 1.9.9 + Jackson 2 API 2.20.0+, your integration will work reliably on Jenkins 2.492.1.