OpenShift Day 4 Guide

Multi-Cluster Management

At Day 4 maturity, you manage a fleet of clusters — dev, staging, prod, regional, edge. Red Hat Advanced Cluster Management (RHACM) and Argo CD ApplicationSets are the two primary tools for managing workloads at scale across clusters.

Red Hat Advanced Cluster Management (RHACM)

RHACM provides a single control plane for fleet visibility, policy enforcement, and application delivery across managed clusters. Managed clusters register as ManagedCluster objects on the hub.

# ManagedClusterSet — logical grouping of clusters (e.g. by region or environment)
apiVersion: cluster.open-cluster-management.io/v1beta2
kind: ManagedClusterSet
metadata:
  name: production-clusters
---
# Placement — selects clusters to target by labels
apiVersion: cluster.open-cluster-management.io/v1beta1
kind: Placement
metadata:
  name: production-placement
  namespace: rhacm-policies
spec:
  clusterSets:
  - production-clusters
  predicates:
  - requiredClusterSelector:
      labelSelector:
        matchExpressions:
        - key: region
          operator: In
          values: ["us-east", "us-west"]
  numberOfClusters: 3          # Select 3 clusters from the matching set

Argo CD ApplicationSet — Fleet Delivery

ApplicationSet generates Argo CD Applications programmatically — one per cluster, environment, or tenant. The cluster generator creates one Application per registered cluster.

apiVersion: argoproj.io/v1alpha1
kind: ApplicationSet
metadata:
  name: api-server-fleet
  namespace: openshift-gitops
spec:
  generators:
  - clusters:
      selector:
        matchLabels:
          env: production                # Target all prod clusters

  - list:                               # Or target explicit clusters
      elements:
      - cluster: us-east-prod
        url: https://us-east.example.com
        namespace: mission-ops
      - cluster: us-west-prod
        url: https://us-west.example.com
        namespace: mission-ops

  template:
    metadata:
      name: 'api-server-{{name}}'
    spec:
      project: production
      source:
        repoURL: https://github.com/example-org/k8s-manifests.git
        targetRevision: main
        path: 'apps/api-server/overlays/{{metadata.labels.env}}'
      destination:
        server: '{{server}}'
        namespace: '{{namespace}}'
      syncPolicy:
        automated:
          prune: true
          selfHeal: true

Cluster Labels Strategy