What is Argo CD and how does it implement GitOps?

Argo CD is a declarative, GitOps continuous delivery tool for Kubernetes, graduated in the CNCF. It implements the pull-based GitOps model: you define Application custom resources that map a Git source to a Kubernetes destination, and Argo CD's Application Controller continuously reconciles the two.

Argo CD's main components:

• API Server: Exposes a gRPC and REST API consumed by the web UI, the argocd CLI, and CI webhooks. Handles authentication (OIDC via Dex or external providers) and authorisation (RBAC).
• Repository Server: Clones Git repositories and renders manifests using whichever tool the Application source specifies — plain YAML, Kustomize, Helm, Jsonnet, or a custom config management plugin.
• Application Controller: The reconciliation engine. Runs a control loop that fetches live Kubernetes resources, compares them to the rendered desired state from the Repository Server, and applies the diff. Emits sync status and health status.
• Redis: Caches rendered manifests and application state to reduce Git and Kubernetes API load.
• Dex (optional): An embedded OIDC identity provider for SSO against GitHub, LDAP, SAML, or other identity providers.

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: guestbook
  namespace: argocd
spec:
  project: default
  source:
    repoURL: https://github.com/org/gitops-config.git
    targetRevision: HEAD
    path: apps/guestbook
  destination:
    server: https://kubernetes.default.svc
    namespace: guestbook
  syncPolicy:
    automated:
      prune: true
      selfHeal: true
    syncOptions:
      - CreateNamespace=true