LAB 02 – Your first application: UI, CLI and YAML

Story: The parcel tracker is the first service to move to GitOps. Its manifests are already in Git (apps/tracker). You try the three ways to create an Argo CD Application – and keep the one that scales.

Duration	~40 min
You create	work/gitops/argocd/tracker.yaml
Solution	solutions/LAB02/ (or ./bin/lab catchup 2)

An Application links a source (repo + revision + path) to a destination (cluster + namespace):

flowchart LR
  S["source<br/>gitea:3000/student/gitops<br/>main · apps/tracker"] --> A((Application<br/>tracker)) --> D["destination<br/>in-cluster · namespace tracker"]

Step 1 – Create it in the UI

+ New App:

Field	Value
Application Name	tracker
Project	default
Sync Options	☑ Auto-Create Namespace
Repository URL	http://gitea:3000/student/gitops.git
Revision / Path	main / apps/tracker
Cluster URL / Namespace	https://kubernetes.default.svc / tracker

Create. The app is OutOfSync and Missing – Argo CD knows the desired state but did not apply anything yet.

Click Sync → Synchronize. Watch the resource tree: Deployment → ReplicaSet → Pod.

✅ Checkpoint: Synced and Healthy; http://tracker.localtest.me shows the blue ParcelPal tracker.

Two different questions: Sync status – does the cluster match Git? Health – does it work (pods ready, ingress has an address…)? An app can be Synced and Degraded at the same time.

Delete the app: Delete, type the name, keep Foreground propagation. The tracker namespace is emptied – the app owned those resources.

Step 2 – The same with the CLI

argocd app create tracker \
  --repo http://gitea:3000/student/gitops.git --revision main --path apps/tracker \
  --dest-server https://kubernetes.default.svc --dest-namespace tracker \
  --sync-option CreateNamespace=true
argocd app get tracker
argocd app sync tracker
argocd app wait tracker --health

Explore: argocd app resources tracker, argocd app manifests tracker, argocd app logs tracker.

Delete it again: argocd app delete tracker --yes.

Step 3 – Declaratively, from Git (the GitOps way)

UI clicks and CLI flags are not reviewed, versioned or reproducible. An Application is just a Kubernetes resource – put it in Git:

cd work/gitops
mkdir -p argocd
cat > argocd/tracker.yaml <<'EOF'
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: tracker
  namespace: argocd
  finalizers:
    - resources-finalizer.argocd.argoproj.io     # deleting the app also deletes its resources
spec:
  project: default
  source:
    repoURL: http://gitea:3000/student/gitops.git
    targetRevision: main
    path: apps/tracker
  destination:
    server: https://kubernetes.default.svc
    namespace: tracker
  syncPolicy:
    syncOptions:
      - CreateNamespace=true
EOF
git add argocd/tracker.yaml && git commit -m "tracker as an Argo CD Application" && git push
kubectl apply -f argocd/tracker.yaml
argocd app sync tracker

Applications always live in the argocd namespace (unless you enable apps in any namespace). The finalizers entry decides what delete means: with it, resources are removed; without it, they are orphaned and keep running.

Step 4 – Change, diff, history, rollback

1. Change the message in Git:

sed -i 's/ParcelPal parcel tracker"/ParcelPal parcel tracker v2"/' apps/tracker/deployment.yaml
git commit -am "tracker v2 message" && git push

1. Refresh in the UI (or argocd app get tracker --refresh) – the app turns OutOfSync. Look at App Diff or:

argocd app diff tracker

1. Sync, then look at the history and roll back to the first revision:

argocd app sync tracker
argocd app history tracker
argocd app rollback tracker 1      # use the ID of the first entry

✅ Checkpoint: the page shows the old message again, and the app is OutOfSync – the cluster now differs from Git.

Rollback is an emergency brake, not a workflow: Git still says "v2". The GitOps way is git revert + sync. (With automated sync – LAB03 – Argo CD refuses to roll back.)

Fix it the GitOps way:

git revert --no-edit HEAD && git push
argocd app sync tracker

✅ Checkpoint: Synced, the message is back to ParcelPal parcel tracker.

Bonus

• kubectl -n argocd get application tracker -o yaml – find status.sync.revision, status.health, status.history.
• Delete with --cascade=false (argocd app delete tracker --cascade=false) and check: do the pods survive? Re-apply argocd/tracker.yaml afterwards – Argo CD adopts them again.

Troubleshooting

Symptom	Likely cause
repository not accessible … no such host	the repo URL must be http://gitea:3000/... – localhost is the pod itself
namespaces "tracker" not found	Auto-Create Namespace / CreateNamespace=true missing
app stays OutOfSync after a push	Argo CD polls every 60 s – press Refresh (LAB03 adds a webhook)
rollback refused: auto-sync is enabled	disable automated sync first (argocd app set tracker --sync-policy none)

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Files for this lab: Think-Cube/argocd-labs/labs/LAB02-first-application