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Overview

Rook is an open-source distributed filesystem designed for use under Kubernetes.

This document serves as a high-level overview or introduction to some basic concepts and patterns surrounding Rook.

All of this is explained in much better detail by their official documentation: https://rook.github.io/docs/rook/master/

Source code is also available here: https://github.com/rook/rook

Getting Started

Now that we've examined each of the pieces, let's zoom out and see what we can do with the whole cluster.

For the quickest quick start, check out the Rook QuickStart guide: https://rook.github.io/docs/rook/master/quickstart.html

Getting Started without an Existing Kubernetes cluster

The easiest way to deploy a new Kubernetes cluster with Rook support on OpenStack (Nebula / SDSC) is to use the https://github.com/nds-org/kubeadm-terraform repository.

This may work for other cloud providers as well, but has not yet been thoroughly tested.

Getting Started on an Existing Kubernetes cluster

The easiest way to get started with Rook on an existing cluster is by using Helm. Helm is a sort of "package manager" for Kubernetes applications.

A Helm chart for Rook can be found here: https://rook.github.io/docs/rook/master/helm.html

Setting up RBAC (Kubernetes 1.9+)

On Kubernetes 1.9+, you will need to configure Rook to use RBAC appropriately.

See https://rook.github.io/docs/rook/master/rbac.html

Monitoring Your Rook Cluster

A glimpse into setting up Prometheus for monitoring Rook: https://rook.github.io/docs/rook/master/monitoring.html

Advanced Configuration

Advanced Configuration options are also documented here: https://rook.github.io/docs/rook/master/advanced-configuration.html

Cluster Teardown

See https://rook.github.io/docs/rook/master/teardown.html for thorough steps on destroying / cleaning up your Rook cluster

Components

Rook runs a number of smaller microservices that run on different nodes in your Kubernetes cluster:

  • The Rook Operator
  • Rook API
  • Ceph Managers / Monitors / OSDs
  • Rook Agents

The Rook Operator

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 and a daemonset for the Object Storage Devices (OSDs).

The operator manages custom resource definitions (CRDs) for pools, object stores (S3/Swift), and file systems 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.

The operator will also watch for desired state changes requested by the api service and apply the changes.

The Rook operator also creates the Rook agents as a daemonset, which runs a pod on each node. 

Ceph Managers / Monitors / OSDs

The operator will start and monitor ceph monitor pods and a daemonset for the OSDs, which provides basic Reliable Autonomic Distributed Object Store (RADOS) storage. 

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. 

Rook Agents

Each agent is a pod deployed on a different Kubernetes node, which configures a Flexvolume plugin that integrates with Kubernetes’ volume controller framework.

All storage operations required on the node are handled such as attaching network storage devices, mounting volumes, and formatting the filesystem.

Storage

Rook provides three types of storage to the Kubernetes cluster:

  • Block Storage: Mount storage to a single pod
  • Object Storage: Expose an S3 API to the storage cluster for applications to put and get data that is accessible from inside or outside the Kubernetes cluster
  • Shared File System: Mount a file system that can be shared across multiple pods

Custom Resource Definitions

Rook also allows you to create and manage your storage cluster through custom resource definitions (CRDs). Each type of resource has its own CRD defined.

  • Cluster: A Rook cluster provides the basis of the storage platform to serve block, object stores, and shared file systems.
  • Pool: A pool manages the backing store for a block store. Pools are also used internally by object and file stores.
  • Object Store: An object store exposes storage with an S3-compatible interface.
  • File System: A file system provides shared storage for multiple Kubernetes pods.

Examples

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