Andrew Mercer
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Fleet is built into Rancher (and installable standalone). It's designed for many clusters — the design target was a million edge clusters.

5.1 Model

GitRepo (fleet-default ns)  ──►  Bundles  ──►  BundleDeployments  ──►  fleet-agent on each cluster
       │                             ▲
       └── targets (cluster selectors, cluster groups)
  • GitRepo: points at a repo, branch/revision and paths.
  • Bundle: Fleet's internal unit — rendered manifests/Helm/Kustomize from one path.
  • ClusterGroup: label selectors over clusters.
  • fleet.yaml: per-path config — Helm values, Kustomize dir, per-target overrides.

5.2 Example

apiVersion: fleet.cattle.io/v1alpha1
kind: GitRepo
metadata:
  name: platform-addons
  namespace: fleet-default
spec:
  repo: https://gitlab.example.net/platform/fleet-addons.git
  branch: main
  paths:
    - cert-manager
    - ingress
    - monitoring
  clientSecretName: gitlab-deploy-token
  targets:
    - name: prod
      clusterSelector:
        matchLabels:
          env: prod
    - name: lab
      clusterGroup: homelab

# monitoring/fleet.yaml
defaultNamespace: cattle-monitoring-system
helm:
  repo: https://charts.rancher.io
  chart: rancher-monitoring
  version: 106.1.2+up69.8.2       # pin explicitly
  releaseName: rancher-monitoring
  values:
    prometheus:
      prometheusSpec:
        retention: 15d
targetCustomizations:
  - name: lab
    clusterGroup: homelab
    helm:
      values:
        prometheus:
          prometheusSpec:
            retention: 3d
            resources:
              requests:
                memory: 1Gi
diff:
  comparePatches:
    - apiVersion: admissionregistration.k8s.io/v1
      kind: MutatingWebhookConfiguration
      operations:
        - {"op": "remove", "path": "/webhooks"}

5.3 Fleet tips

  • Bundle status Modified usually means drift (something mutated a resource) — use diff.comparePatches for known benign mutations.
  • Use dependsOn in fleet.yaml to order bundles (e.g. CRDs before CRs).
  • helm.takeOwnership: true lets Fleet adopt pre-existing releases.
  • Fleet can manage cluster definitions themselves (the provisioning.cattle.io objects above) when pointed at the local cluster — true "clusters as code."
  • Polling is default; configure webhooks from GitLab/GitHub for near-instant sync.

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