Demo Kubernetes Deploy Update Image Tag

In this tutorial, we’ll automate updating the Docker image tag in Kubernetes manifests and commit changes back to a GitOps repository using a Jenkins pipeline, triggered by Git webhooks.

Prerequisites

1. Inspect the Manifest Repository

Open the Gitea repo solar-system-gitops-argo-cd and navigate to the kubernetes folder:

Examine deployment.yml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: solar-system
  namespace: solar-system
spec:
  replicas: 2
  template:
    spec:
      containers:
      - name: solar-system
        image: siddharth67/solar-system:3e9063be059342b1916f020e034344fb267d1
        imagePullPolicy: Always
        ports:
        - containerPort: 3000

2. Check Argo CD Application Status

Argo CD will show the application as OutOfSync before resources are applied:

Verify no resources exist in the solar-system namespace:

kubectl get all -n solar-system

3. Jenkins Pipeline: Add “K8S Update Image Tag” Stage

Add a new declarative stage to your Jenkinsfile to:

• Run only on pull request branches (PR*).
• Clone the GitOps repo.
• Update the Docker image tag in deployment.yml.
• Commit & push to feature-$BUILD_ID.

stage('K8S Update Image Tag') {
  when { branch 'PR*' }
  steps {
    script {
      if (fileExists('solar-system-gitops-argo-cd')) {
        sh 'rm -rf solar-system-gitops-argo-cd'
      }
    }
    sh 'git clone -b main http://64.227.187.25:5555/dasher-org/solar-system-gitops-argo-cd'
    dir('solar-system-gitops-argo-cd/kubernetes') {
      sh '''
        git checkout main
        git checkout -b feature-$BUILD_ID

        sed -i "s#image: .*#image: siddharth67/solar-system:$GIT_COMMIT#g" deployment.yml
        git config user.email "[email protected]"
        git config user.name "Jenkins"
        git remote set-url origin http://[email protected]:5555/dasher-org/solar-system-gitops-argo-cd
        git add deployment.yml
        git commit -m "Update Docker image to $GIT_COMMIT"
        git push -u origin feature-$BUILD_ID
      '''
    }
  }
  post {
    always {
      script {
        if (fileExists('solar-system-gitops-argo-cd')) {
          sh 'rm -rf solar-system-gitops-argo-cd'
        }
      }
    }
  }
}

4. Configure Gitea API Token

4.1 Generate Token in Gitea

In Gitea user settings, create a new access token named jenkins-token with read/write scope:

4.2 Add Token to Jenkins Credentials

Go to Credentials > System > Global credentials in Jenkins and add a Secret text credential with ID gitea-api-token:

Reference it:

environment {
  GITEA_TOKEN = credentials('gitea-api-token')
}

5. Webhook Trigger on Pull Requests

Configure a Gitea webhook to trigger Jenkins on pull request events:

Enable Pull request events:

5.1 Create a Pull Request

Open a new PR against main:

5.2 Observe Jenkins Pipeline Runs

Jenkins will build the PR branch and run the image update:

View the pipeline activity dashboard:

6. Confirm Image Tag Update

Check console logs:

git clone -b main http://64.227.187.25:5555/dasher-org/solar-system-gitops-argo-cd
git checkout -b feature-1
sed -i "... deployment.yml"
git commit -am "Update Docker image to f5c47d71240f57467b284288f1c452f81341b"
git push -u origin feature-1

Inspect the feature-1 branch in Gitea:

7. Sync with Argo CD

Since Argo CD tracks main, it remains OutOfSync until you merge feature-1:

Next, automate merging feature-1 into main so Argo CD can deploy the updated manifest.

Links and References

• Kubernetes Documentation
• Argo CD User Guide
• Jenkins Pipeline Syntax
• Gitea Webhooks

Thank you for following this GitOps workflow!