Sharing a File between Containers

By default, all containers within a Kubernetes Pod share the same filesystem. In this tutorial, we'll demonstrate how to create a file in an Ubuntu container and then read it from a Node.js container within the same Pod using a Jenkins pipeline.

Jenkins Pipeline Configuration

Paste the following pipeline definition into your Jenkinsfile to set up two containers—ubuntu-container and node-container—in a single Pod:

pipeline {
  agent {
    kubernetes {
      yaml """
apiVersion: v1
kind: Pod
spec:
  containers:
  - name: ubuntu-container
    image: ubuntu
    command: ['sleep']
    args: ['infinity']
  - name: node-container
    image: node:18-alpine
    command: ['cat']
    tty: true
"""
      defaultContainer 'ubuntu-container'
    }
  }

  stages {
    stage('Create File on Ubuntu') {
      steps {
        sh '''
          # Display the hostname
          hostname

          # Write data to a file
          echo important_UBUNTU_data > ubuntu-$BUILD_ID.txt

          # Confirm the file was created
          ls -ltr ubuntu-$BUILD_ID.txt
        '''
      }
    }

    stage('Access File on Node') {
      steps {
        container('node-container') {
          sh '''
            # Verify Node.js and npm versions
            node -v
            npm -v

            # List and read the file created earlier
            ls -ltr ubuntu-$BUILD_ID.txt
            cat ubuntu-$BUILD_ID.txt
          '''
        }
      }
    }
  }
}

Pipeline in Action

Once you commit and run this pipeline, Jenkins will create the Pod and execute both stages. The Ubuntu container writes ubuntu-$BUILD_ID.txt, and the Node.js container reads it immediately afterward.

According to the Kubernetes Pod Lifecycle documentation, all containers in a Pod can share volumes and files.

Console Output Example

Below is an excerpt from the Jenkins console log illustrating how the file is shared between containers:

[ubuntu-container] Running shell script
+ hostname
k8s-cloud-agent-demo-5-rv7b8-8frt0-n41pw
+ echo important_UBUNTU_data
+ ls -ltr ubuntu-5.txt
-rw-r--r-- 1 root root 22 Nov 10 09:47 ubuntu-5.txt

[node-container] Running shell script
+ node -v
v18.20.4
+ npm -v
8.19.2
+ ls -ltr ubuntu-5.txt
-rw-r--r-- 1 root root 22 Nov 10 09:47 ubuntu-5.txt
+ cat ubuntu-5.txt
important_UBUNTU_data

Comparing Jenkins Agent Strategies

Choose the right Jenkins agent model based on your infrastructure and maintenance requirements:

Links and References

• Kubernetes Pod Lifecycle
• Jenkins Kubernetes Plugin
• Docker Official Images