ArgoCD App of Apps Demo

This repository demonstrates the App of Apps pattern with ArgoCD for OpenShift deployments.

Architecture Overview

┌─────────────────────────────────────────────────────────────────────┐
│                          Hub Cluster                                 │
│  ┌─────────────────────────────────────────────────────────────┐    │
│  │                    OpenShift GitOps                          │    │
│  │                                                              │    │
│  │  demo-apps-root (Application)                                │    │
│  │       │                                                      │    │
│  │       ├── Creates: AppProject (demo-apps)                    │    │
│  │       ├── Creates: Application (httpd-demo)  ──────┐        │    │
│  │       ├── Creates: Application (pacman)      ──────┼────────┼────┼──► CT1 Cluster
│  │       └── Creates: Application (guestbook)   ──────┘        │    │
│  │                                                              │    │
│  └─────────────────────────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────────────────────┘
                                    │
                                    │ Manages
                                    ▼
┌─────────────────────────────────────────────────────────────────────┐
│                          CT1 Cluster                                 │
│                                                                      │
│  ┌─────────────────┐  ┌─────────────────┐  ┌─────────────────┐     │
│  │   httpd-demo    │  │     pacman      │  │    guestbook    │     │
│  │   namespace     │  │   namespace     │  │   namespace     │     │
│  │                 │  │                 │  │                 │     │
│  │  - Deployment   │  │  - MongoDB      │  │  - Redis Leader │     │
│  │  - Service      │  │  - Pacman App   │  │  - Redis Follow │     │
│  │  - Route        │  │  - Service      │  │  - Frontend     │     │
│  │                 │  │  - Route        │  │  - Route        │     │
│  └─────────────────┘  └─────────────────┘  └─────────────────┘     │
└─────────────────────────────────────────────────────────────────────┘

Repository Structure

argo-apps-demo/
├── base/                           # App of Apps root
│   ├── kustomization.yaml          # Kustomize configuration
│   ├── appproject.yaml             # ArgoCD AppProject
│   ├── app-httpd-demo.yaml         # Application CR for httpd
│   ├── app-pacman.yaml             # Application CR for pacman
│   └── app-guestbook.yaml          # Application CR for guestbook
│
├── apps/                           # Application manifests
│   ├── httpd-demo/                 # Apache HTTPD demo
│   │   ├── kustomization.yaml
│   │   ├── namespace.yaml
│   │   ├── deployment.yaml
│   │   ├── service.yaml
│   │   └── route.yaml
│   │
│   ├── pacman/                     # Pacman game demo
│   │   ├── kustomization.yaml
│   │   ├── namespace.yaml
│   │   ├── mongodb-*.yaml          # MongoDB backend
│   │   └── pacman-*.yaml           # Pacman frontend
│   │
│   └── guestbook/                  # Classic K8s demo
│       ├── kustomization.yaml
│       ├── namespace.yaml
│       ├── redis-leader-*.yaml     # Redis leader
│       ├── redis-follower-*.yaml   # Redis followers
│       └── guestbook-*.yaml        # Guestbook frontend
│
└── README.md

Demo Applications

1. HTTPD Demo

Simple Apache web server using Red Hat's UBI image.

• Namespace: httpd-demo
• Replicas: 2
• Image: registry.redhat.io/rhel8/httpd-24:latest

2. Pacman

Classic arcade game with MongoDB backend for high scores.

• Namespace: pacman
• Components: MongoDB + Node.js frontend
• Image: quay.io/jpacker/nodejs-pacman-app:latest

3. Guestbook

Classic Kubernetes demo with Redis backend.

• Namespace: guestbook
• Components: Redis leader + followers + PHP frontend
• Image: gcr.io/google_samples/gb-frontend:v5

Deployment

Prerequisites

1. Hub cluster with OpenShift GitOps installed
2. CT1 cluster registered in Hub ArgoCD
3. Network connectivity between clusters

Deploy via Hub ArgoCD

The root application should be deployed from the Hub cluster:

# Apply the root application from the argo-demo repo
oc apply -f clusters/hub/demo-apps-root-application.yaml

Or add to the hub's kustomization.yaml:

resources:
  - demo-apps-root-application.yaml

Verify Deployment

# Check Application status in Hub
oc get applications -n openshift-gitops

# Check deployed resources on CT1
oc get all -n httpd-demo
oc get all -n pacman
oc get all -n guestbook

# Get application routes
oc get routes -n httpd-demo
oc get routes -n pacman
oc get routes -n guestbook

App of Apps Pattern Benefits

1. Single Point of Management: Deploy multiple applications with one root Application
2. GitOps Native: All configuration stored in Git
3. Scalable: Easy to add new applications
4. Consistent: All apps follow same deployment patterns
5. Self-Healing: ArgoCD automatically reconciles drift

Customization

Adding New Applications

1. Create application manifests in apps/<app-name>/
2. Add Application CR in base/app-<app-name>.yaml
3. Update base/kustomization.yaml resources
4. Update base/appproject.yaml destinations if needed

Environment-Specific Overlays

Create overlays for different environments:

overlays/
├── dev/
│   └── kustomization.yaml
├── staging/
│   └── kustomization.yaml
└── prod/
    └── kustomization.yaml

Troubleshooting

Common Issues

1. Application stuck in Unknown state

   • Verify cluster connectivity
   • Check ArgoCD has access to target cluster

2. Sync failed - namespace not found

   • Ensure CreateNamespace=true in syncOptions

3. Image pull errors

   • Verify image registry access
   • Check pull secrets if using private registry

Useful Commands

# Force sync an application
argocd app sync demo-apps-root --prune

# Get application details
argocd app get httpd-demo

# View sync history
argocd app history pacman

# Refresh application
argocd app get guestbook --refresh

License

Apache 2.0