Migrating from Jenkins running in Kubernetes to CloudBees CI on modern cloud platforms

Issue

You are currently running Jenkins in Kubernetes and you would like to learn the steps to migrate that controller to be running with CloudBees CI on modern cloud platforms.

Environment

Resolution

In the below steps, we will backup Jenkins, install CloudBees CI, create a managed controller, and restore the Jenkins backup into that controller.

Locate your Jenkins pod, exec into it and take a backup of JENKINS_HOME, and copy it outside of the pod:

kubectl exec -ti jenkins-0 -c jenkins -n jenkins -- sh
cd /var/jenkins_home
tar -cf - * | gzip > /tmp/backup-jenkins-1.tar.gz
exit
kubectl cp -c jenkins -n jenkins jenkins-0:/tmp/backup-jenkins-1.tar.gz backup-jenkins-1.tar.gz

Align the Jenkins and CloudBees CI app versions between the V.R.M fields (in this example, 2.401.3) to ensure a smooth migration.

If you are not sure which CloudBees CI chart version to install, run:
```
helm list -A | grep jenkins
jenkins         jenkins         1               2023-07-27 17:32:34.451193 -0400 EDT    deployed        jenkins-4.4.2                           2.401.3
```
Then use the app version from the output, in this example it’s 2.401.3, and use it to find the corresponding CloudBees CI chart:
```
helm repo add cloudbees https://public-charts.artifacts.cloudbees.com/repository/public/
helm repo update
helm search repo cloudbees/cloudbees-core --versions | grep 2.401.3
cloudbees/cloudbees-core        3.13430.0+1e383c33d1a3  2.401.3.3       Enterprise Continuous Integration with Jenkins
```
Based on this output, when you install CloudBees CI, you would pass --version 3.13430.0+1e383c33d1a3 to your helm command.

To install CloudBees CI, follow the Installing section of the CloudBees CI documentation.
Now that CloudBees CI is installed at the correct version, use your operations center to provision a new managed controller:
- The default version will match the app version you installed, in this case 2.401.3.3, this should match the Jenkins version (just the V.R.M fields)
- Choose a large enough disk size to hold your existing Persistent Volume used for Jenkins
- Ensure Provision and start on save is checked (which is the default), then click Save to provision your CloudBees CI Managed controller:
On your CloudBees CI managed controller, use the Install suggested plugins option, then choose New Item, enter a job name, for example restore, and choose the Backup and Restore job type:

Under Build Steps choose Restore from backup, then choose the Local directory with Directory set to /tmp. Under Restore options, Advanced check the NOT RECOMMENDED: Ignore digest check (we are only checking this option since the backup was not taken using the CloudBees Backup plugin)
Copy the Jenkins backup into your CloudBees CI managed controller pod (it’s important the backup name matches the pattern backup-.*-[0-9]+\.[tar\.gz|zip]):
```
kubectl cp -n cloudbees backup-jenkins-1.tar.gz CONTROLLER_NAME-0:/tmp/backup-jenkins-1.tar.gz
```
Ensure you have an agent to run the build on (can be any agent), and run the restore job, at the end of the restore job log click the link to restart the controller:
After the restart, all of your configuration, and jobs will be available on your CloudBees CI managed controller, and you can start to make use of CloudBees CI features.

Tested product/plugin versions

Jenkins Chart: jenkins-4.4.2, App Version: 2.401.3
CloudBees CI Chart: cloudbees-core-3.13430.0+1e383c33d1a3, App Version: 2.401.3.3