Ceph Storage

Ceph is a highly scalable distributed storage solution for block storage, object storage, and shared filesystems with years of production deployments.

Design

Rook enables Ceph storage systems to run on Kubernetes using Kubernetes primitives. The following image illustrates how Ceph Rook integrates with Kubernetes:

With Ceph running in the Kubernetes cluster, Kubernetes applications can mount block devices and filesystems managed by Rook, or can use the S3/Swift API for object storage. The Rook operator automates configuration of storage components and monitors the cluster to ensure the storage remains available and healthy.

The Rook operator is a simple container that has all that is needed to bootstrap and monitor the storage cluster. The operator will start and monitor Ceph monitor pods, the Ceph OSD daemons to provide RADOS storage, as well as start and manage other Ceph daemons. The operator manages CRDs for pools, object stores (S3/Swift), and filesystems by initializing the pods and other artifacts necessary to run the services.

The operator will monitor the storage daemons to ensure the cluster is healthy. Ceph mons will be started or failed over when necessary, and other adjustments are made as the cluster grows or shrinks. The operator will also watch for desired state changes requested by the api service and apply the changes.

The Rook operator also initializes the agents that are needed for consuming the storage. Rook automatically configures the Ceph-CSI driver to mount the storage to your pods. Rook’s flex driver is also available, though it is not enabled by default and will soon be deprecated in favor of the CSI driver.

The rook/ceph image includes all necessary tools to manage the cluster – there is no change to the data path. Rook does not attempt to maintain full fidelity with Ceph. Many of the Ceph concepts like placement groups and crush maps are hidden so you don’t have to worry about them. Instead Rook creates a much simplified user experience for admins that is in terms of physical resources, pools, volumes, filesystems, and buckets. At the same time, advanced configuration can be applied when needed with the Ceph tools.

Rook is implemented in golang. Ceph is implemented in C++ where the data path is highly optimized. We believe this combination offers the best of both worlds.