Argo CD Lab - OpenShift GitOps¶

60 min Intermediate

In this lab you'll practice GitOps with Red Hat OpenShift GitOps, Red Hat's supported distribution of Argo CD. You'll deploy the bootcamp's greeting app from manifests in Git, watch Argo CD correct drift in the cluster, and roll out changes by committing to Git instead of running oc.

Prerequisites¶

• An OpenShift 4.16+ cluster with the Red Hat OpenShift GitOps operator installed. If it isn't installed and you're a cluster administrator, see Install the operator.
• The oc CLI, logged in to the cluster.
• The argocd CLI. Install it with brew install argocd on macOS, or download it from the Argo CD releases.
• A GitHub account.

Install the operator¶

Skip this section if OpenShift GitOps is already installed. Check with oc get argocd -n openshift-gitops.

oc apply -f - <<'EOF'
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: openshift-gitops-operator
  namespace: openshift-operators
spec:
  channel: latest
  name: openshift-gitops-operator
  source: redhat-operators
  sourceNamespace: openshift-marketplace
EOF

The operator creates a ready-to-use Argo CD instance in the openshift-gitops namespace:

oc get pods -n openshift-gitops
oc get route openshift-gitops-server -n openshift-gitops

Setup¶

1. Fork the repository¶

Argo CD deploys whatever is in Git, so you need a repository you can push to. Fork the bootcamp repository to your GitHub account, then clone your fork:

export GITHUB_USER=<your-github-username>
git clone https://github.com/${GITHUB_USER}/cloud-native-bootcamp.git
cd cloud-native-bootcamp
ls sample-app/gitops

deployment.yaml  route.yaml  service.yaml

These three manifests are the desired state of the app: a Deployment of the greeting image, a Service, and a TLS Route.

2. Create the target project¶

oc new-project gitops-lab
oc label namespace gitops-lab argocd.argoproj.io/managed-by=openshift-gitops

The label lets the default Argo CD instance manage resources in gitops-lab. Without it, syncs fail with a forbidden error.

3. Log in to Argo CD¶

echo "https://$(oc get route openshift-gitops-server -n openshift-gitops -o jsonpath='{.spec.host}')"

ARGOCD_SERVER=$(oc get route openshift-gitops-server -n openshift-gitops -o jsonpath='{.spec.host}')
ARGOCD_PASSWORD=$(oc get secret openshift-gitops-cluster -n openshift-gitops -o jsonpath='{.data.admin\.password}' | base64 -d)
argocd login "${ARGOCD_SERVER}" --username admin --password "${ARGOCD_PASSWORD}" --grpc-web --insecure

Part 1: Create an Application¶

An Argo CD Application links a path in a Git repository to a namespace in a cluster.

1. Save this Application as greeting-app.yaml. It's written for your fork:

   greeting-app.yaml

   apiVersion: argoproj.io/v1alpha1
   kind: Application
   metadata:
     name: greeting
     namespace: openshift-gitops
   spec:
     project: default
     source:
       repoURL: https://github.com/GITHUB_USER/cloud-native-bootcamp.git
       targetRevision: main
       path: sample-app/gitops
     destination:
       server: https://kubernetes.default.svc
       namespace: gitops-lab
   

2. Put in your GitHub username and create the Application:

   sed -i.bak "s/GITHUB_USER/${GITHUB_USER}/" greeting-app.yaml
   oc apply -f greeting-app.yaml
   

3. Check the Application's status in the UI or with the CLI:

   argocd app get openshift-gitops/greeting
   

   It shows Sync Status: OutOfSync and Health Status: Missing. Argo CD has compared Git with the cluster and found that none of the resources exist yet. With no sync policy, it only reports the difference.

4. Sync the Application to make the cluster match Git. Click Sync > Synchronize in the UI, or run:

   argocd app sync openshift-gitops/greeting
   argocd app wait openshift-gitops/greeting --health
   

5. Check the app:

   oc get deployment,service,route -n gitops-lab
   curl -sk "https://$(oc get route greeting -n gitops-lab -o jsonpath='{.spec.host}')/greeting?name=GitOps"
   

   {"message":"Deployed by Argo CD","name":"GitOps"}
   

Part 2: Automated sync and self-healing¶

1. Turn on automated sync with prune (delete resources that were removed from Git) and self-heal (undo manual changes in the cluster):

   argocd app set openshift-gitops/greeting --sync-policy automated --auto-prune --self-heal
   

   Declaratively, that's this block in the Application's spec:

   syncPolicy:
     automated:
       prune: true
       selfHeal: true
   

2. Simulate someone "fixing" production by hand:

   oc scale deployment/greeting --replicas=3 -n gitops-lab
   oc get deployment greeting -n gitops-lab -w
   

   Within a few seconds, Argo CD notices that the cluster has drifted from Git and scales the Deployment back to 1 replica. Press Ctrl+C to stop watching.

Part 3: Change the app through Git¶

In GitOps, Git is the only way to change what runs.

1. In your clone, edit sample-app/gitops/deployment.yaml: set replicas: 2 and change the GREETING value to a message of your own.

2. Commit and push:

   git add sample-app/gitops/deployment.yaml
   git commit -m "Scale greeting to 2 replicas and update message"
   git push
   

3. Argo CD polls Git every 3 minutes. Click Refresh in the UI, or run argocd app get openshift-gitops/greeting --refresh, to check right away. Watch the new replicas roll out:

   oc get pods -n gitops-lab -l app=greeting
   curl -sk "https://$(oc get route greeting -n gitops-lab -o jsonpath='{.spec.host}')/greeting"
   

4. See the deployment history. Each sync records the Git commit it deployed:

   argocd app history openshift-gitops/greeting
   

5. Roll back the GitOps way: revert the commit and push. Argo CD brings the cluster back in line with Git.

   git revert --no-edit HEAD
   git push
   

Part 4: Prune¶

1. Delete sample-app/gitops/route.yaml from your fork, then commit and push.
2. After the next sync, the Route is gone from the cluster (oc get route -n gitops-lab), because prune is on.
3. Restore it with git revert --no-edit HEAD && git push.

Cleanup¶

oc delete -f greeting-app.yaml       # deletes the Application only
oc delete project gitops-lab

What you learned¶

• Declaring an Argo CD Application that points at a Git path
• Manual vs. automated sync, self-heal and prune
• Changing and rolling back an application by committing to Git
• How CI (building images) and CD (GitOps) fit together

Additional resources¶

• Red Hat OpenShift GitOps documentation
• Argo CD documentation
• OpenGitOps principles