Rook

Source Code

github.com/rook/rook

Rook is the Kubernetes operator that manages the Ceph cluster in CobaltCore. It runs Ceph daemons (monitors, managers, OSDs, MDS, RGW) as containerized Kubernetes workloads and provides declarative management through CRDs.

Why Rook?

Running Ceph as a Kubernetes workload means the cluster lifecycle - initial deployment, scaling, upgrades, and self-healing - is handled by Kubernetes controllers rather than manual playbooks. Rook bridges the gap between Ceph's daemon model and Kubernetes' declarative model.

How Rook manages Ceph

You describe the desired cluster state in a CephCluster CRD. Rook reconciles the running Ceph daemons to match that state:

Installation

Prerequisites

• Kubernetes 1.25+
• Raw block devices available on storage nodes (unformatted, no filesystem)
• Network connectivity between storage nodes

Install the operator

helm repo add rook-release https://charts.rook.io/release
helm repo update

helm install --create-namespace \
  --namespace rook-ceph \
  rook-ceph rook-release/rook-ceph

Deploy the Ceph cluster

Create a CephCluster resource. A minimal 3-node cluster:

apiVersion: ceph.rook.io/v1
kind: CephCluster
metadata:
  name: rook-ceph
  namespace: rook-ceph
spec:
  cephVersion:
    image: quay.io/ceph/ceph:v18
  dataDirHostPath: /var/lib/rook
  mon:
    count: 3
    allowMultiplePerNode: false
  mgr:
    count: 1
  storage:
    useAllNodes: true
    useAllDevices: true

Apply it and watch the cluster form:

kubectl apply -f ceph-cluster.yaml
kubectl get cephcluster -n rook-ceph -w

Create storage classes

RBD (block):

kubectl apply -f https://raw.githubusercontent.com/rook/rook/refs/heads/release-1.17/deploy/examples/csi/rbd/storageclass.yaml

CephFS (file):

kubectl apply -f https://raw.githubusercontent.com/rook/rook/refs/heads/release-1.17/deploy/examples/csi/cephfs/storageclass.yaml

Replace release-1.17 with the Rook version you installed.

Verify

First install the Rook toolbox to get access to ceph CLI commands:

kubectl apply -f https://raw.githubusercontent.com/rook/rook/refs/heads/release-1.17/deploy/examples/toolbox.yaml
kubectl rollout status deployment/rook-ceph-tools -n rook-ceph

Then check cluster health:

# Check cluster health
kubectl exec deployment/rook-ceph-tools -n rook-ceph -- ceph status

# List OSDs
kubectl exec deployment/rook-ceph-tools -n rook-ceph -- ceph osd tree

A healthy cluster reports HEALTH_OK.

Troubleshooting

Symptom	Common cause
Operator pod not starting	Missing RBAC or CRDs not installed
OSDs not starting	Disk already has a filesystem; must be raw
HEALTH_WARN: too few PGs	Pool PG count needs adjustment for cluster size
Monitors not forming quorum	Network partitioning between nodes

For stretched-cluster quorum in multi-site deployments, see Storage - Arbiter.

See also

• Storage - Ceph
• Storage - Arbiter
• Rook documentation