How do you implement multi-cluster GitOps at scale?

Multi-cluster GitOps adds the dimension of which cluster to deploy to on top of the standard single-cluster model. The two dominant approaches are hub-spoke (a central GitOps control plane manages all clusters) and decentralised (each cluster runs its own GitOps operator, all watching the same or related Git repos).

Argo CD hub-spoke: A single Argo CD instance (the "hub") in a management cluster registers all target clusters using argocd cluster add. Applications or ApplicationSets declare their destination.server as the registered cluster API URL. The hub's Application Controller communicates with each target cluster's API server directly. An ApplicationSet with the cluster generator creates one Application per registered cluster automatically.

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: platform-addons
  namespace: argocd
spec:
  generators:
    - clusters:
        selector:
          matchLabels:
            tier: production
  template:
    metadata:
      name: "{{name}}-platform-addons"
    spec:
      project: platform
      source:
        repoURL: https://github.com/org/gitops-config.git
        targetRevision: main
        path: "clusters/{{metadata.labels.region}}/addons"
      destination:
        server: "{{server}}"
        namespace: platform-system

Flux decentralised: Each cluster runs its own Flux controllers, bootstrapped from a management cluster or a bootstrap script. A "management" cluster's Flux can push Flux configs to leaf clusters by managing their Flux Kustomization CRs via the Kubernetes API or GitOps itself.

Scaling considerations: Shard the Argo CD Application Controller by cluster to handle hundreds of clusters. Use AppProjects or Flux tenancy to enforce namespace-level isolation per team. Keep a separate Git directory structure per cluster (or cluster tier) to make blast-radius clear — a change to clusters/prod-us-east-1/ only affects that cluster.

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