Upgrading Jenkins in CI

'legacy' setup for ci.centos.org

We follow the Jenkins LTS branch for the version we run, and we so have to update jenkins itself, or some plugins, when some CVEs, security fixes are announced, and also to comply with some other internal rules for CI/CD platform.

The process is easy for that part:

• announce the maintenance window to the ci-users list
• proceed with the adhoc-upgrade-jenkins.yml playbook
• verify that jenkins is back online and agents (re)connected
• announce on the ci-users list that maintenance is complete

Openshift setup