GitOps Sample App

Inspired by this awesome playlist GitOps and K8s بالعربي.

Table of Contents

• Main Challenges
• Prerequisites
• Application Endpoints
• The CI Workflow
• The Manifests
• Further Reading

Main Challenges

#	Challenge	Artifact
1	Build a Go web app that displays deployment metadata (version, commit, build time, env, pod, node)	gitops-sample-app
2	Create a multi-stage Dockerfile with build args for metadata injection	Dockerfile
3	Create Kustomize manifests with base + per-environment overlays (dev/prod)	gitops-sample-app-manifests
4	Inject pod/node metadata automatically using Kubernetes Downward API	base/deployment.yaml
5	Build a CI pipeline that builds/pushes Docker image and updates the manifests repo	ci.yaml
8	Trigger CI on PR merge (dev) and semver tags (prod)	ci.yaml
9	Configure ArgoCD Applications for auto-sync with prune and self-heal	application.yml
10	Separate namespaces per environment to avoid resource collisions	overlays/

Prerequisites

Cluster

• Kubernetes cluster (Minikube, Kind, EKS, GKE, etc.)
• ArgoCD installed and configured
• kubectl access to the cluster

Note: This project was tested and created on Minikube with Kubernetes v1.35.

Client

• Go 1.25+
• Docker
• git
• make
• Docker Hub account with access token

Application Endpoints

The app is simple — it provides information about the current deployment (version, commit_sha, build_time, environment, pod_name, node_name, host_ip, request_count) and runtime details (go_version, uptime).

type AppInfo struct {
	Version     string `json:"version"`
	GitCommit   string `json:"git_commit"`
	BuildTime   string `json:"build_time"`
	Environment string `json:"environment"`
	PodName     string `json:"pod_name"`
	NodeName    string `json:"node_name"`
	HostIP      string `json:"host_ip"`
	GoVersion   string `json:"go_version"`
	Uptime      string `json:"uptime"`
	RequestCount int64  `json:"request_count"`
}

Endpoint	Description
GET /	HTML dashboard
GET /healthz	Health check (JSON)
GET /api/info	All metadata (JSON)

HTML Dashboard

API Response

The CI Workflow

The pipeline is defined in .github/workflows/ci.yaml and consists of two jobs:

Triggers

Event	Target	Image Tag	Updates
PR merged to main	Dev	<commit-sha>	overlays/dev
Tag push v*	Prod	v1.x.x	overlays/prod

Jobs

1. build-and-push

• Checks out the app code
• Extracts build metadata (version, commit SHA, build time)
• Logs in to Docker Hub
• Builds and pushes the Docker image with the appropriate tag + latest

2. update-manifests

• Checks out the manifests repo

• Updates newTag in the target overlay's kustomization.yaml using sed:

  sed -i "s|newTag:.*|newTag: <new-tag>|" kustomization.yaml

  • sed -i — edit the file in-place
  • s|pattern|replacement| — substitute (using | as delimiter instead of /)
  • newTag:.* — match newTag: followed by anything
  • newTag: <new-tag> — replace with the new image tag (commit SHA or semver)

• Commits and pushes the change, triggering ArgoCD to sync

Required Secrets

Secret	Description
DOCKERHUB_USERNAME	Docker Hub username
DOCKERHUB_TOKEN	Docker Hub access token
MANIFESTS_PAT	GitHub PAT with repo scope for the manifests repo

Flow

PR merged to main ──► build-and-push ──► update overlays/dev ──► ArgoCD syncs dev
Tag v1.x.x pushed ──► build-and-push ──► update overlays/prod ──► ArgoCD syncs prod

The Manifests

The Kubernetes manifests live in a separate repo: gitops-sample-app-manifests.

Base

Shared resources used by all environments: Namespace, Deployment, Service, and ConfigMap. The Deployment uses envFrom to load the ConfigMap and the Kubernetes Downward API to inject POD_NAME and NODE_NAME.

Overlays

Each overlay sets its own namespace to avoid resource collisions:

Overlay	Namespace	Image Tag	Replicas	APP_ENV
dev	gitops-sample-app-dev	<commit-sha>	1	development
prod	gitops-sample-app-prod	v1.x.x	3	production

ArgoCD Applications

Both environments are defined in application.yml with automated sync policy, prune, and selfHeal enabled. ArgoCD watches the manifests repo and automatically applies changes when the CI updates the image tag.

# application.yml
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: gitops-sample-app-dev
  namespace: argocd
spec:
  project: default
  source:
    repoURL: https://github.com/moabdelazem/gitops-sample-app-manifests.git
    targetRevision: main
    path: overlays/dev
  destination:
    server: https://kubernetes.default.svc
    namespace: gitops-sample-app-dev
  syncPolicy:
    automated:
      prune: true
      selfHeal: true
    syncOptions:
      - CreateNamespace=true
---
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: gitops-sample-app-prod
  namespace: argocd
spec:
  project: default
  source:
    repoURL: https://github.com/moabdelazem/gitops-sample-app-manifests.git
    targetRevision: main
    path: overlays/prod
  destination:
    server: https://kubernetes.default.svc
    namespace: gitops-sample-app-prod
  syncPolicy:
    automated:
      prune: true
      selfHeal: true
    syncOptions:
      - CreateNamespace=true

Further Reading

• ArgoCD Documentation
• Kustomize Documentation
• GitHub Actions Documentation
• Kubernetes Downward API
• Docker Multi-Stage Builds
• Go ldflags
• GitOps Principles