Chapter 2. Architecture of OpenShift Data Foundation
Red Hat OpenShift Data Foundation provides services for, and can run internally from the Red Hat OpenShift Container Platform.
Figure 2.1. Red Hat OpenShift Data Foundation architecture
Red Hat OpenShift Data Foundation supports deployment into Red Hat OpenShift Container Platform clusters deployed on installer-provisioned or user-provisioned infrastructure.
For details about these two approaches, see OpenShift Container Platform - Installation process.
To know more about interoperability of components for Red Hat OpenShift Data Foundation and Red Hat OpenShift Container Platform, see Red Hat OpenShift Data Foundation Supportability and Interoperability Checker.
For information about the architecture and lifecycle of OpenShift Container Platform, see OpenShift Container Platform architecture.
For IBM Power, see OpenShift Container Platform - Installation process.
2.1. About operators
Red Hat OpenShift Data Foundation comprises of three main operators, which codify administrative tasks and custom resources so that you can easily automate the task and resource characteristics. Administrators define the desired end state of the cluster, and the OpenShift Data Foundation operators ensure the cluster is either in that state, or approaching that state, with minimal administrator intervention.
OpenShift Data Foundation operator
A meta-operator that draws on other operators in specific tested ways to codify and enforce the recommendations and requirements of a supported Red Hat OpenShift Data Foundation deployment. The rook-ceph and noobaa operators provide the storage cluster resource that wraps these resources.
Rook-ceph operator
This operator automates the packaging, deployment, management, upgrading, and scaling of persistent storage and file, block, and object services. It creates block and file storage classes for all environments, and creates an object storage class and services Object Bucket Claims (OBCs) made against it in on-premises environments.
Additionally, for internal mode clusters, it provides the ceph cluster resource, which manages the deployments and services representing the following:
- Object Storage Daemons (OSDs)
- Monitors (MONs)
- Manager (MGR)
- Metadata servers (MDS)
- RADOS Object Gateways (RGWs) on-premises only
Multicloud Object Gateway operator
This operator automates the packaging, deployment, management, upgrading, and scaling of the Multicloud Object Gateway (MCG) object service. It creates an object storage class and services the OBCs made against it.
Additionally, it provides the NooBaa cluster resource, which manages the deployments and services for NooBaa core, database, and endpoint.
2.2. Storage cluster deployment approaches
The growing list of operating modalities is an evidence that flexibility is a core tenet of Red Hat OpenShift Data Foundation. This section provides you with information that will help you to select the most appropriate approach for your environments.
You can deploy Red Hat OpenShift Data Foundation either entirely within OpenShift Container Platform (Internal approach) or to make available the services from a cluster running outside of OpenShift Container Platform (External approach).
2.2.1. Internal approach
Deployment of Red Hat OpenShift Data Foundation entirely within Red Hat OpenShift Container Platform has all the benefits of operator based deployment and management. You can use the internal-attached device approach in the graphical user interface (GUI) to deploy Red Hat OpenShift Data Foundation in internal mode using the local storage operator and local storage devices.
Ease of deployment and management are the highlights of running OpenShift Data Foundation services internally on OpenShift Container Platform. There are two different deployment modalities available when Red Hat OpenShift Data Foundation is running entirely within Red Hat OpenShift Container Platform:
- Simple
- Optimized
Simple deployment
Red Hat OpenShift Data Foundation services run co-resident with applications. The operators in Red Hat OpenShift Container Platform manages these applications.
A simple deployment is best for situations where,
- Storage requirements are not clear.
- Red Hat OpenShift Data Foundation services runs co-resident with the applications.
- Creating a node instance of a specific size is difficult, for example, on bare metal.
In order for Red Hat OpenShift Data Foundation to run co-resident with the applications, the applications must have local storage devices, or portable storage devices attached to them dynamically, like EBS volumes on EC2, or vSphere Virtual Volumes on VMware, or SAN volumes.
PowerVC dynamically provisions the SAN volumes.
Optimized deployment
Red Hat OpenShift Data Foundation services run on dedicated infrastructure nodes. Red Hat OpenShift Container Platform manages these infrastructure nodes.
An optimized approach is best for situations when,
- Storage requirements are clear.
- Red Hat OpenShift Data Foundation services run on dedicated infrastructure nodes.
- Creating a node instance of a specific size is easy, for example, on cloud, virtualized environment, and so on.
2.2.2. External approach
Red Hat OpenShift Data Foundation exposes the Red Hat Ceph Storage services running outside of the OpenShift Container Platform cluster as storage classes.
The external approach is best used when,
- Storage requirements are significant (600+ storage devices).
- Multiple OpenShift Container Platform clusters need to consume storage services from a common external cluster.
- Another team, Site Reliability Engineering (SRE), storage, and so on, needs to manage the external cluster providing storage services. Possibly pre-existing.
2.3. Node types
Nodes run the container runtime, as well as services, to ensure that the containers are running, and maintain network communication and separation between the pods. In OpenShift Data Foundation, there are three types of nodes.
| Node Type | Description |
|---|---|
| Master | These nodes run processes that expose the Kubernetes API, watch and schedule newly created pods, maintain node health and quantity, and control interaction with underlying cloud providers. |
| Infrastructure (Infra) | Infra nodes run cluster level infrastructure services such as logging, metrics, registry, and routing. These are optional in OpenShift Container Platform clusters. In order to separate OpenShift Data Foundation layer workload from applications, ensure that you use infra nodes for OpenShift Data Foundation in virtualized and cloud environments.
To create Infra nodes, you can provision new nodes labeled as |
| Worker | Worker nodes are also known as application nodes since they run applications. When OpenShift Data Foundation is deployed in internal mode, you require a minimal cluster of 3 worker nodes. Make sure that the nodes are spread across 3 different racks, or availability zones, to ensure availability. In order for OpenShift Data Foundation to run on worker nodes, you need to attach the local storage devices, or portable storage devices to the worker nodes dynamically. When OpenShift Data Foundation is deployed in external mode, it runs on multiple nodes. This allows Kubernetes to reschedule on the available nodes in case of a failure. |
OpenShift Data Foundation requires the same number of subsciptions as OpenShift Container Platform. However, if OpenShift Data Foundation is running on infra nodes, OpenShift does not require OpenShift Container Platform subscription for these nodes. Therefore, the OpenShift Data Foundation control plane does not require additional OpenShift Container Platform and OpenShift Data Foundation subscriptions. For more information, see Chapter 6, Subscriptions.
