GitOps with ArgoCD

GitOps is an operational framework that uses Git as the single source of truth for declarative infrastructure and applications. ArgoCD is the most popular GitOps tool for Kubernetes. This lesson covers GitOps principles, ArgoCD architecture, Application CRDs, sync strategies, and multi-cluster management.

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GitOps Principles

Principle	Description
Declarative	The entire system is described declaratively in Git
Versioned and immutable	Git provides an audit trail of every change
Pulled automatically	Agents pull desired state from Git, not pushed by CI
Continuously reconciled	Drift is detected and corrected automatically

┌─────────────────────────────────────────────────────────────┐
│                      GitOps Workflow                        │
│                                                             │
│  Developer ──▶ Git Commit ──▶ Git Repo ──▶ ArgoCD ──▶ K8s │
│                                   ▲                   │    │
│                                   │                   │    │
│                                   └── Drift detected ─┘    │
└─────────────────────────────────────────────────────────────┘

GitOps vs Traditional CI/CD

Aspect	Traditional CI/CD	GitOps
Deployment	CI pushes to cluster	Agent pulls from Git
Source of truth	CI pipeline config	Git repository
Drift detection	Manual / none	Automatic, continuous
Rollback	Re-run old pipeline	Git revert
Audit trail	Pipeline logs	Git history

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Installing ArgoCD

# Create namespace
kubectl create namespace argocd

# Install ArgoCD
kubectl apply -n argocd -f https://raw.githubusercontent.com/argoproj/argo-cd/stable/manifests/install.yaml

# Wait for pods to be ready
kubectl wait --for=condition=ready pod -l app.kubernetes.io/name=argocd-server -n argocd --timeout=120s

# Get initial admin password
kubectl -n argocd get secret argocd-initial-admin-secret -o jsonpath="{.data.password}" | base64 -d

# Access the UI (port-forward)
kubectl port-forward svc/argocd-server -n argocd 8080:443

# Login via CLI
argocd login localhost:8080

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ArgoCD Architecture

┌───────────────────────────────────────────────────┐
│                    ArgoCD                          │
│                                                   │
│  ┌──────────────┐  ┌──────────────────────────┐  │
│  │  API Server  │  │  Application Controller  │  │
│  │  (UI + CLI)  │  │  (reconciliation loop)   │  │
│  └──────────────┘  └──────────────────────────┘  │
│  ┌──────────────┐  ┌──────────────────────────┐  │
│  │  Repo Server │  │  Redis (cache)           │  │
│  │  (Git clone) │  │                          │  │
│  └──────────────┘  └──────────────────────────┘  │
└───────────────────────────────────────────────────┘
         │                      │
         ▼                      ▼
  ┌─────────────┐      ┌──────────────┐
  │  Git Repo   │      │  Kubernetes  │
  │  (desired)  │      │  (actual)    │
  └─────────────┘      └──────────────┘

Component	Role
API Server	Exposes the UI and CLI API
Application Controller	Watches Applications, compares desired vs actual
Repo Server	Clones Git repos and renders manifests
Redis	Caches Git repo data for performance

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Application CRD

The Application resource is the core of ArgoCD — it defines what to deploy and where.