Jenkins slave on K8S

Use K8S as Jenkins slave/agent via Jenkins kubernetes plugin. (continuous integration)

• From Jenkins master, install Kubernetes plugin (This plugin integrates Jenkins with Kubernetes)
• Credentials -> Add Credentials -> Kind: Secret file (kubeconfig file from K8S)
• Manage Jenkins -> Manage Nodes and Cloud -> Configure Clouds (new version of Jenkins) 

1. Credentials: select Secret file name just created from drop-down menu, and Test Connection
2. Jenkins URL and tunnel match Jenkins master. No need https:// for tunnel
3. Pod label will be used for slave pod label in K8S
4. Pod Template: name will be prefix for slave pod name prefix in K8S; blank namespace will create slave pod in default namespace in K8S;
5. Pod Template -> Labels is critical, which help Jenkins master decides which builder will be used for the build job. 
6. Pod Template: Usage: only builds job with label expression matching this label
7. Define container template details: name: jnlp; docker image: jenkins/jnlp-slave:latest; working directory: /home/jenkins/; also environment variable value pair: {JENKINS_URL: http://jenkins-master:8080} (or adding other agent as Pod Template)

When creating a new build job, check Restrict where this project can be run, enter Label expression: Pod template label in previous step 5, so Jenkins master will use K8S pod to execute build task.

Jenkins slave started in K8S, then terminated in K8S after build job completes with proper pod retention setting in Pod Template.

Use K8S as Jenkins slave via Jenkin Kubernetes Continuous Deploy Plugin (continuous deployment on kubernetes)

• From Jenkins master, install Kubernetes Continuous Deploy Plugin
• Credentials -> Add Credentials -> Kind: Kubernetes Configuration (KubeConfig); directly copy content of  kubeconfig file into textext. The ID of this Jenkins credential will match value of  kubeconfigId in file: Jenkinsfile, which is in source code Repositories, such as github, or private repository
• If Kubernetes plugin is already configured, no more configuration is required.

When creating a new pipeline in Jenkins, in Pipeline section: select Pipeline script from SCM, then select proper SCM, repository and branch. Default script path is: Jenkinsfile

Jenkins pipeline checkout source from SCM, and start slave pod on K8S to build images and upload container images into registry such Docker hub or any private/public registry defined in Jenkinsfile from SCM. Then slave pod on K8S is terminated with the completion of Continuous Integration/Delivery process. Finally, pipeline script will deploy app Pod via manifest in Jenkinsfile, always pulling container images from registry.