Rook is a Kubernetes operator that deploys and manages storage systems — primarily Ceph — as native Kubernetes resources. The distinction: Ceph is the storage system; Rook is the Kubernetes wiring around it.

Without Rook you would run Ceph manually (or via cephadm) and then configure the Kubernetes CSI driver separately. Rook collapses that into CRDs and handles the full lifecycle: deployment, configuration, expansion, upgrades, and failure recovery.

How it works

Rook introduces several CRDs:

CephCluster — declares the cluster: which nodes, which disks to use as OSDs, replication settings.

CephBlockPool — defines a Ceph pool (replication factor, failure domain). Maps to an RBD pool.

StorageClass — references a CephBlockPool and enables dynamic PVC provisioning. Kubernetes workloads request storage; Rook/Ceph fulfils it.

CephFilesystem — deploys CephFS + MDS for POSIX shared filesystem access.

CephObjectStore — deploys the Ceph RGW S3-compatible object storage gateway.

Typical install sequence

kubectl apply -f https://raw.githubusercontent.com/rook/rook/refs/tags/v1.17.9/deploy/examples/crds.yaml
kubectl apply -f https://raw.githubusercontent.com/rook/rook/refs/tags/v1.17.9/deploy/examples/common.yaml
kubectl apply -f https://raw.githubusercontent.com/rook/rook/refs/tags/v1.17.9/deploy/examples/operator.yaml

Then apply a CephCluster manifest declaring your storage topology, followed by CephBlockPool and StorageClass for PVC support.

Single-node considerations

A single-node setup requires allowMultiplePerNode: true in the CephCluster spec (MONs, MGR, and OSDs all land on the same node). Replication size must be set to 1 — there is nowhere else to replicate. This works for experimentation; it is not a production configuration. See Ceph for details on the replication model.

Related

• Rook documentation
• Ceph — the underlying storage system
• Rook + Ceph in the homelab