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Addons

Butler manages cluster addons through a Helm-based catalog system. Addons extend cluster functionality with networking, storage, ingress, monitoring, and other capabilities.

Addon Types​

Platform Addons​

Required for cluster operation. Butler installs these automatically during cluster creation. They cannot be removed through the Console or CLI.

AddonPurpose
CiliumCNI networking (pod-to-pod communication)
MetalLBLoadBalancer Services (on-prem clusters only)
kube-vipControl plane virtual IP (on-prem management clusters)

Optional Addons​

Users install and remove these through TenantCluster spec, the Console, or directly via TenantAddon CRDs.

CategoryAvailable Addons
StorageLonghorn, OpenEBS
IngressTraefik, nginx-ingress
Certificatescert-manager
MonitoringPrometheus, Victoria Metrics
GitOpsFlux, ArgoCD

How It Works​

Three CRDs drive the addon system:

AddonDefinition -- Cluster-scoped catalog entries. Each definition specifies a Helm chart repository, chart name, available versions, default values, and whether the addon is a platform requirement. Platform admins manage the catalog.

TenantAddon -- Namespaced resources that represent an addon installed on a specific tenant cluster. Butler creates TenantAddons from TenantCluster.spec.addons or users can create them directly. The butler-controller installs the Helm chart on the tenant cluster and tracks its health.

ManagementAddon -- Cluster-scoped resources for addons installed on the management cluster itself (Steward, CAPI providers, monitoring stack).

Specifying Addons​

Define addons in the TenantCluster spec:

spec:
  addons:
    cni:
      provider: cilium
      version: "1.17.0"
    loadBalancer:
      provider: metallb
      version: "0.14.9"
    storage:
      provider: longhorn
      version: "1.7.0"
    certManager:
      enabled: true
      version: "1.16.0"

Each addon's version field is required. Butler does not auto-select versions.

See Also​