KCNA — ArgoCD and Flux

3 minute read

ArgoCD and Flux

ArgoCD and Flux are the two leading GitOps tools for Kubernetes. Both are CNCF Graduated projects that continuously reconcile the desired state in Git with the actual state in the cluster.

ArgoCD

What Is ArgoCD?

ArgoCD is part of the Argo project (CNCF Graduated). It’s a declarative, GitOps continuous delivery tool for Kubernetes.

Architecture

┌──────────────────────────────────────────────┐
│              ArgoCD (in cluster)               │
│                                                │
│  ┌───────────────┐  ┌───────────────────────┐ │
│  │  Repo Server   │  │  Application          │ │
│  │ (clone Git     │  │  Controller           │ │
│  │  repos,render  │  │  (watch & reconcile)  │ │
│  │  manifests)    │  │                       │ │
│  └───────┬───────┘  └──────────┬────────────┘ │
│          │                     │               │
│  ┌───────▼─────────────────────▼──────────┐   │
│  │              API Server                 │   │
│  │  (gRPC/REST API + Web UI + CLI)        │   │
│  └────────────────────────────────────────┘   │
└──────────────────────────────────────────────┘
         │                          │
         ▼                          ▼
    Git Repository            Kubernetes Cluster
    (desired state)           (actual state)

Key Features

Feature Description
Web UI Visual dashboard showing app status, sync state, and resource tree
Multi-cluster Manage applications across multiple Kubernetes clusters
SSO Integration OIDC, SAML, LDAP, GitHub/GitLab authentication
RBAC Fine-grained access control per project/application
Sync Policies Auto-sync, manual sync, self-heal, prune
Manifest Sources Helm, Kustomize, plain YAML, Jsonnet

ArgoCD Application

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: my-app
  namespace: argocd
spec:
  project: default
  source:
    repoURL: https://github.com/org/my-app-config.git
    targetRevision: main
    path: k8s/overlays/production
  destination:
    server: https://kubernetes.default.svc
    namespace: production
  syncPolicy:
    automated:
      prune: true       # Delete resources removed from Git
      selfHeal: true    # Revert manual changes

Sync Strategies

Strategy Description
Manual Sync You click “Sync” in the UI or run argocd app sync
Auto-Sync ArgoCD automatically applies changes when Git changes
Self-Heal Reverts manual changes made directly to the cluster
Prune Deletes resources that exist in the cluster but not in Git

Flux

What Is Flux?

Flux is a CNCF Graduated GitOps toolkit. It’s a set of controllers that keep Kubernetes clusters in sync with Git repositories.

Architecture

Flux uses a modular controller-based architecture:

Git Repository
     │
     ▼
┌────────────────┐
│ Source          │ ← Watches Git repos, Helm repos, OCI registries
│ Controller     │
└───────┬────────┘
        │
        ▼
┌────────────────┐
│ Kustomize      │ ← Applies Kustomize overlays
│ Controller     │
├────────────────┤
│ Helm           │ ← Manages Helm releases
│ Controller     │
└───────┬────────┘
        │
        ▼
  Kubernetes Cluster

Key Components

Controller Purpose
Source Controller Fetches manifests from Git repos, Helm repos, OCI registries
Kustomize Controller Reconciles Kustomize manifests on the cluster
Helm Controller Manages Helm chart releases
Notification Controller Handles alerts and notifications (Slack, Teams, webhooks)
Image Automation Controller Detects new container images and updates Git

Flux GitRepository + Kustomization

# Source: Watch a Git repository
apiVersion: source.toolkit.fluxcd.io/v1
kind: GitRepository
metadata:
  name: my-app
  namespace: flux-system
spec:
  interval: 1m
  url: https://github.com/org/my-app-config.git
  ref:
    branch: main
---
# Apply: Reconcile manifests from the source
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
  name: my-app
  namespace: flux-system
spec:
  interval: 5m
  path: ./k8s/production
  prune: true
  sourceRef:
    kind: GitRepository
    name: my-app

ArgoCD vs Flux

Aspect ArgoCD Flux
CNCF Status Graduated (Argo project) Graduated
UI Built-in Web UI with resource visualization No built-in UI (use Weave GitOps or Grafana dashboards)
Architecture Monolithic (single deployment) Modular (separate controllers)
Multi-cluster Native support via Application Sets Requires additional setup
Manifest Sources Helm, Kustomize, Jsonnet, plain YAML Helm, Kustomize, plain YAML
Image Automation Argo Image Updater (separate) Built-in Image Automation Controller
CLI argocd CLI flux CLI
Best For Teams that value a visual UI and multi-cluster management Teams that prefer a lightweight, modular, CLI-driven approach

Both tools achieve the same goal — GitOps continuous delivery — and the choice depends on team preference.

Common GitOps Patterns

App of Apps (ArgoCD)

A parent ArgoCD Application manages child Applications:

# Parent app manages all team applications
apps/
├── app-of-apps.yaml      # Parent Application
├── frontend-app.yaml     # Child Application
├── backend-app.yaml      # Child Application
└── database-app.yaml     # Child Application

Multi-Tenancy (Flux)

Each team gets its own Git source and namespace:

clusters/
├── team-a/
│   ├── source.yaml
│   └── kustomization.yaml
├── team-b/
│   ├── source.yaml
│   └── kustomization.yaml

KCNA Exam Tips

  • Both ArgoCD and Flux are CNCF Graduated GitOps tools
  • ArgoCD has a built-in Web UI; Flux does not
  • Both support Helm and Kustomize as manifest sources
  • Know what auto-sync and self-heal do in ArgoCD
  • Flux uses a modular controller architecture (Source, Kustomize, Helm controllers)
  • Both implement pull-based GitOps — the agent runs inside the cluster
  • Know the difference between manual sync and auto-sync

What’s Next?

Learn deployment strategies — how to safely release new versions with minimal risk.

Next: Deployment Strategies →

Updated:

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