Kubernetes pod is not communicating back to Jenkins

Question

I am learning Kubernetes and installed Jenkins and Minikube on my local Mac machine. As as exercise, I am trying to launch Kubernetes pods as Jenkins agents and used the Kubernetes Jenkins plugin for that. I am able to successfully connect Minikube cluster from Jenkins and create one sample job having pipeline script:

pipeline {
 agent {
  kubernetes {
  yaml '''
    apiVersion: v1
    kind: Pod
    spec:
      containers:
      - name: jnlp
        image: maven:alpine
        command:
        - cat
        tty: true
    '''
  }
}
stages {
  stage('Run maven') {
   steps {
    container('maven') {
      sh 'mvn -version'
       }
     }
   }
  }
 }

When ran the job, the pod is successfully launched and the Jenkins agent is created, but the pod is not able to communicate back to Jenkins and appears offline.

Console:

[Pipeline] Start of Pipeline
[Pipeline] podTemplate
[Pipeline] {
[Pipeline] node
Created Pod: kubernetes default/testjob-21-3t8r7-ttlkn-m51gt
Still waiting to schedule task
‘testjob-21-3t8r7-ttlkn-m51gt’ is offline
Aborted by user
[Pipeline] // node
[Pipeline] }
[Pipeline] // podTemplate
[Pipeline] End of Pipeline
org.jenkinsci.plugins.workflow.actions.ErrorAction$ErrorId: 79f30007-01fc-42e8-a5df- 220b01bbf32c
Finished: ABORTED

Answer 1

The issue you're facing, where the Jenkins agent pod is not able to communicate back to Jenkins and remains offline, might have various causes, here are some steps you can take to troubleshoot and resolve the issue:

Check Network Policies: Ensure that there are no network policies preventing communication between Jenkins and the pods in your Kubernetes cluster.

Service Account Permissions: Verify that the service account used by the Jenkins agent pod has the necessary permissions to connect back to Jenkins. The service account should have the edit or view role on the namespace where Jenkins is deployed.

Jenkins URL Configuration: In the Jenkins global configuration, make sure that the "Jenkins URL" is correctly configured. The Jenkins URL should be accessible from within the Kubernetes cluster, and the Jenkins service should be reachable.

Firewall Rules: Check if there are any firewall rules or network restrictions preventing communication between Jenkins and the Kubernetes cluster. Ensure that the necessary ports are open.

Pod Logs: Retrieve the logs from the Jenkins agent pod to identify any error messages or connectivity issues. You can use the following command to view the logs of the pod:

$ kubectl logs <pod-name>

Check Jenkins Configuration: Review the Jenkins Kubernetes plugin configuration. Ensure that the plugin is configured with the correct Kubernetes URL, Jenkins URL, and namespace.

Pod Configuration: Update your Jenkins agent pod configuration to include the Jenkins URL. Modify your pipeline script to include the Jenkins URL in the pod template:

pipeline {
  agent {
    kubernetes {
      yaml '''
        apiVersion: v1
        kind: Pod
        spec:
          containers:
          - name: jnlp
            image: maven:alpine
            command:
            - cat
            tty: true
          metadata:
            annotations:
              jenkins/jenkinsUrl: "http://jenkins-url/"
      '''
    }
  }
  stages {
    // Your stages
  }
}

**Replace "http://jenkins-url/" with the actual URL of your Jenkins instance.

Jenkins Plugins: Ensure that you have the latest version of the Jenkins Kubernetes plugin installed. Check for any updates or bug fixes related to connectivity issues.

Kubernetes Cluster Reachability: Verify that the Jenkins pod in the Kubernetes cluster can reach the Jenkins master. You can use tools like curl or telnet from within the pod to check connectivity.

DNS Resolution: Ensure that DNS resolution is working correctly within the Kubernetes cluster. The Jenkins agent pod should be able to resolve the Jenkins master's hostname.

Proxy Configuration: If your environment uses a proxy, make sure that the Jenkins agent pod is configured to use the proxy if needed.

By systematically checking these points, I hope you will be able to identify the root cause of the communication issue between the Jenkins agent pod and Jenkins.