Your First Application: Sync and Health

1. 1

   Write the manifests

   The same Deployment you wrote in the Kubernetes course, with probes and resources. nginxdemos/hello stands in for the ShopLite web image; it shows its version in the page, so you can watch deploys happen.

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: web
     labels: { app: web }
   spec:
     replicas: 2
     selector:
       matchLabels: { app: web }
     template:
       metadata:
         labels: { app: web }
       spec:
         containers:
           - name: web
             image: nginxdemos/hello:0.3
             ports: [{ containerPort: 80 }]
             readinessProbe:
               httpGet: { path: /, port: 80 }
             resources:
               requests: { cpu: 50m, memory: 32Mi }
               limits: { memory: 64Mi }

2. 2

   And the Service

   A ClusterIP Service in front of the pods.

   apiVersion: v1
   kind: Service
   metadata:
     name: web
   spec:
     selector: { app: web }
     ports: [{ port: 80, targetPort: 80 }]

3. 3

   Declare the Application

   The Application itself is YAML too, and it lives in the same repo, so even 'what Argo CD manages' is in Git. CreateNamespace=true lets Argo create shoplite-dev. There's no automated block yet, so Argo will only report differences; you'll sync by hand first to see each step.

   apiVersion: argoproj.io/v1alpha1
   kind: Application
   metadata:
     name: web-dev
     namespace: argocd
   spec:
     project: default
     source:
       repoURL: https://github.com/<you>/shoplite-gitops.git
       targetRevision: main
       path: apps/web
     destination:
       server: https://kubernetes.default.svc
       namespace: shoplite-dev
     syncPolicy:
       syncOptions:
         - CreateNamespace=true

4. 4

   Push, register, and sync

   After this one-time kubectl apply of the Application, you won't use kubectl to deploy again. Before the first sync, the app is OutOfSync and Missing: Git has resources the cluster doesn't.

   terminalcopy cmd

   $ git add . && git commit -m 'web: initial deploy to dev' && git push

   kubectl apply -f argocd/web-dev.yaml

   argocd app get web-dev | grep -E 'Sync Status|Health'

   argocd app sync web-dev

   argocd app wait web-dev --health

   ── expected output ──

   Sync Status: OutOfSync from main (a1b2c3d)

   Health Status: Missing

   ...

   GROUP KIND NAMESPACE NAME STATUS HEALTH HOOK MESSAGE

   Service shoplite-dev web Synced Healthy service/web created

   apps Deployment shoplite-dev web Synced Progressing deployment.apps/web created

   ...

   Health Status: Healthy

5. 5

   Deploy by commit

   Change the image tag in Git. That's the whole deploy. Argo polls repos every 3 minutes by default; a Git webhook to /api/webhook makes it near-instant. argocd app diff shows exactly what will change, like terraform plan.

   terminalcopy cmd

   $ sed -i 's/hello:0.3/hello:0.4/' apps/web/deployment.yaml

   git commit -am 'web: 0.3 → 0.4' && git push

   argocd app diff web-dev --refresh

   argocd app sync web-dev && argocd app history web-dev

   ── expected output ──

   ===== apps/Deployment shoplite-dev/web ======

   < image: nginxdemos/hello:0.3

   > image: nginxdemos/hello:0.4

   ...

   ID DATE REVISION

   0 2026-09-26 10:02:11 +0530 IST main (a1b2c3d)

   1 2026-09-26 10:09:47 +0530 IST main (d4e5f6a)

6. 6

   Roll back the GitOps way

   argocd app rollback exists, but it makes the cluster differ from Git, and with auto-sync on (next mission) Argo would immediately undo it. The GitOps rollback is git revert: history shows exactly who rolled back, when, and why.

   terminalcopy cmd

   $ git revert --no-edit HEAD && git push

   argocd app sync web-dev

   kubectl -n shoplite-dev get deploy web -o jsonpath='{.spec.template.spec.containers[0].image}'

   ── expected output ──

   nginxdemos/hello:0.3

Make each change, run the command, and read the error before revealing the diagnosis. Recognising these messages on sight is what makes you fast on a real team. Undo the change afterwards.