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Chapter 1. Understanding DCN

Note

An upgrade from Red Hat OpenStack Platform (RHOSP) 17.1 to Red Hat OpenStack Services on OpenShift (RHOSO) 18.0.3 is not currently supported for Distributed Compute Node (DCN) deployments.

Distributed compute node (DCN) architecture is for edge use cases that require Compute and storage nodes to be deployed remotely while sharing a centralized control plane. With DCN architecture, you can position workloads strategically closer to your operational needs for higher performance.

The central location consists of, at a minimum, the RHOSO control plane installed on a Red Hat OpenShift Container Platform (RHOCP) cluster. Compute nodes can also be deployed at the central location. The edge locations consist of Compute and optional storage nodes.

DCN architecture consists of multiple availability zones (AZs) to ensure isolation per-site scheduling of the OpenStack resources.

You configure each site with a unique AZ. In this guide, the central site uses az0, the first edge location uses az1, and so on. You can use any naming convention to ensure that the AZ names are unique per site.

Figure 1.1. Basic distributed compute node architecture with storage

Illustration showing the central site connected to three remote sites with storage.

DCN architecture is a hub-and-spoke routed network deployment. DCN is comparable to a spine-leaf deployment for routed provisioning and control plane networking with RHOSO.

  • The hub is the central site with core routers and a datacenter gateway (DC-GW). The hub hosts the control plane which manages the geographically dispersed sites.
  • The spokes are the remote edge sites. Each site is defined by using an OpenStackDataPlaneNodeSet custom resource. Red Hat Ceph Storage (RHCS) is used as the storage back end. You can deploy RHCS in either a hyperconverged configuration, or as a standalone storage back end.

When you launch an instance at an edge site, the required image is copied to the local Image service (glance) store automatically. You can copy images from the central Image store to edge sites by using glance multistore to save time during instance launch.

1.1. Required software for DCN architecture
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Verify that your environment meets the minimum software version requirements for distributed compute node (DCN) architecture. Meeting these requirements ensures compatibility and support for your distributed deployment.

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Table 1.1. Required software versions for DCN architecture
PlatformVersionOptional

Red Hat OpenShift Container Platform

4.16

No

Red Hat Enterprise Linux

9.2

No

Red Hat OpenStack Platform

18.0.3

No

Red Hat Ceph Storage

7 or 8

Yes

1.2. DCN storage
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Choose from three storage deployment configurations for your central and edge locations. Each configuration option provides different trade-offs between performance, capacity, and operational complexity.

  • Without storage.
  • Using hyperconverged Ceph storage.
  • Using Red Hat Ceph Storage (RHCS) as a standalone storage backend.

The storage you deploy is dedicated to the site you deploy it on. DCN architecture uses an Image service (glance) pod, and a Block Storage service (cinder) pod for each site, deployed at the central location, on the Red Hat OpenShift Container Platform (RHOCP) cluster.

For edge sites deployed without storage, you can use the aggregate cache command to store images in the Compute service (nova) cache. Caching Image service images in the Compute service provides faster boot times for instances by avoiding the process of downloading images across a WAN link.

Example: 

$ openstack aggregate cache image <dcn0> <myimage>
  • Replace <dcn0> with the name of your availability zone.
  • Replace <myimage> with the name of your image.
Note

Red Hat OpenStack Services on OpenShift (RHOSO) supports external deployments of Red Hat Ceph Storage 7, 8, and 9. Configuration examples that reference Red Hat Ceph Storage use Release 7 information. If you are using a later version of Red Hat Ceph Storage, adjust the configuration examples accordingly.

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