GitOps architecture

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Table of Contents

1. Components of a GitOps architecture
2. Deployment flow
3. Architecture patterns
4. Multi-cluster
5. High availability
6. Hands-on exercises

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1 - Components of a GitOps architecture

Overview

Key components

Component	Role	Examples
GitOps Controller	Reconciliation	Argo CD, Flux
Git Repository	Source of truth	GitHub, GitLab
Image Registry	Image storage	Docker Hub, ECR, GCR
Secrets Manager	Secrets management	Vault, Sealed Secrets
CI Pipeline	Build and tests	GitHub Actions, Jenkins

The GitOps Controller

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2 - Deployment flow

Complete workflow

Detailed steps

# 1. Développeur pousse du code
git push origin feature/new-api

# 2. CI Pipeline se déclenche
- Build de l'application
- Tests unitaires et intégration
- Build de l'image Docker
- Push vers le registry

# 3. CI met à jour le repo GitOps
yq -i '.spec.template.spec.containers[0].image = "myapp:sha123"' \
  gitops-repo/apps/myapp/deployment.yaml
git commit && git push

# 4. GitOps Agent détecte le changement
# (ArgoCD/Flux poll toutes les 3 minutes par défaut)

# 5. Agent applique les changements
kubectl apply -f deployment.yaml

# 6. Kubernetes tire l'image et déploie

Repository separation

Repository	Content	Access
App Source	Application code	Developers
GitOps Config	K8s manifests	Platform team
Helm Charts	Shared charts	Platform team

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3 - Architecture patterns

Pattern 1: Monorepo

gitops-monorepo/
├── apps/
│   ├── frontend/
│   ├── backend/
│   └── worker/
├── infrastructure/
│   ├── monitoring/
│   └── ingress/
└── environments/
    ├── dev/
    ├── staging/
    └── prod/

Pros	Cons
Unified view	Complex permissions
Atomic commits	Large repo
Clear dependencies	Slower CI/CD

Pattern 2: Polyrepo

# Repos séparés
org/gitops-apps
org/gitops-infra
org/gitops-monitoring
org/gitops-env-prod
org/gitops-env-staging

Pros	Cons
Fine-grained permissions	Fragmented view
Fast CI/CD	Complex coordination
Autonomous teams	Possible duplication

Pattern 3: App of Apps

# apps/root-app.yaml
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: root-app
spec:
  source:
    path: apps
  destination:
    namespace: argocd
---
# apps/frontend.yaml, backend.yaml, etc.
# Chaque fichier est une Application ArgoCD

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4 - Multi-cluster

Hub-spoke architecture

Multi-cluster ArgoCD configuration

# Enregistrer un cluster
apiVersion: v1
kind: Secret
metadata:
  name: prod-cluster
  labels:
    argocd.argoproj.io/secret-type: cluster
type: Opaque
stringData:
  name: prod-cluster
  server: https://prod-cluster.example.com
  config: |
    {
      "bearerToken": "...",
      "tlsClientConfig": {
        "insecure": false,
        "caData": "..."
      }
    }

# Application ciblant un cluster spécifique
apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: myapp-prod
spec:
  destination:
    server: https://prod-cluster.example.com
    namespace: default

ApplicationSet for multi-cluster

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: myapp
spec:
  generators:
    - list:
        elements:
          - cluster: dev
            url: https://dev.example.com
          - cluster: staging
            url: https://staging.example.com
          - cluster: prod
            url: https://prod.example.com
  template:
    metadata:
      name: 'myapp-{{cluster}}'
    spec:
      destination:
        server: '{{url}}'
        namespace: default
      source:
        path: 'apps/myapp/overlays/{{cluster}}'

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5 - High availability

ArgoCD HA

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

# Composants HA :
# - 3 replicas argocd-server
# - 3 replicas argocd-repo-server
# - 3 replicas argocd-application-controller (avec sharding)
# - Redis HA

Considerations

Component	HA Strategy
Git Repo	Native GitHub/GitLab HA
ArgoCD Server	Multiple replicas + LB
Controller	Sharding per cluster
Redis	Redis Sentinel/Cluster

Disaster Recovery

# Backup ArgoCD
argocd admin export > backup.yaml

# Restore
argocd admin import < backup.yaml

# Backup Git = le repo lui-même
git clone --mirror [email protected]:org/gitops-repo.git

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6 - Hands-on exercises

Quiz

Q1. What are the two types of repositories in a GitOps architecture?

Answer

1. App Source Repository: Contains the application code
2. GitOps Config Repository: Contains the declarative Kubernetes manifests

Q2. What is the "App of Apps" pattern?

Answer

A "root" ArgoCD Application that deploys other ArgoCD Applications. It allows managing all applications from a single entry point.

Exercise: Architecture design

Design the GitOps architecture for:

• 10 microservices
• 3 environments
• 2 production clusters (for HA)

Suggested solution

gitops-repo/
├── apps/
│   ├── service1/
│   │   ├── base/
│   │   └── overlays/
│   │       ├── dev/
│   │       ├── staging/
│   │       └── prod/
│   └── ... (10 services)
├── infrastructure/
└── applicationsets/
    └── all-services.yaml  # ApplicationSet pour multi-cluster

Use ApplicationSet to automatically deploy to the 2 production clusters.

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Key takeaways

• Components: GitOps Controller, Git Repo, Image Registry, Secrets Manager
• Separate App Source and GitOps Config repos
• Patterns: Monorepo, Polyrepo, App of Apps
• Multi-cluster: Hub-spoke architecture, ApplicationSet
• HA: Replicas, sharding, Redis Sentinel

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