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Chapter 3. Architecture overview

This is a reference architecture for running Red Hat OpenShift Container Platform 4.4 on Red Hat OpenStack Platform 13 or Red Hat OpenStack Platform 16.0.

3.1. Installing Red Hat OpenStack Platform

Red Hat OpenStack Platform (RHOSP) is deployed to physical servers using the RHOSP director. Director is a toolset for installing and managing a complete RHOSP environment from installation to Day 2 operations.

3.2. Installing Red Hat OpenShift Container Platform 4.x

Red Hat OpenShift Container Platform (RHOCP) has a new installation program for the 4.x stream. It features a streamlined interface and simplified installation process allowing a faster, easier, and more precise installation. For more information, see the Red Hat OpenShift Container Platform 4.4 Installing guide.

The RHOCP 4 installation program offers the following types of deployment:

  • Installer-provisioned infrastructure clusters: The RHOCP 4 installation program manages all aspects of the installation, including infrastructure provisioning, with a RHOCP best practice deployment.
  • User-provisioned infrastructure clusters: Administrators are responsible for preparing, creating and managing their own underlying infrastructure for clusters. This approach allows greater customization prior to installing RHOCP.

Both types of clusters have the following characteristics:

  • Highly available infrastructure with no single points of failure by default.
  • A deep integration between RHOCP and the underlying operating system, Red Hat Enterprise Linux CoreOS (RHCOS), that provides “appliance-like” integration.
  • Administrators maintain control over what updates are applied, and when.

This reference architecture features the installer-provisioned infrastructure method for installing RHOCP onto RHOSP. Following this method, the installation program creates all the networking, machines, and operating systems required when using the OpenStack APIs. This results in an architecture that is highly available, fully tested, and entirely supported, suitable for production today.

  • The new installer-provisioned infrastructure method for RHOCP is highly prescriptive, as it installs a “best practice” deployment. The infrastructure of an installer-provisioned infrastructure deployment should not be customised after deployment. Any infrastructure changes must be implemented by the installation program, which interacts directly with the underlying infrastructure and APIs. Only Day 2 infrastructure operations, such as machine scale outs, are recommended.
  • For enterprises that need additional infrastructure customisations and requirements, the simplicity of the installer-provisioned infrastructure method may be limiting. In this case, the user-provisioned infrastructure method may be more appropriate.

This document describes a reference architecture suitable for the majority of RHOCP 4.4 on RHOSP use cases. The reference architecture represents the best practice for getting RHOCP on RHOSP up and running quickly and in the most reliable and supported way. It also shares important design considerations and key integrations between the products.

This reference architecture is fully supported by Red Hat.

3.3. Relationship between Red Hat OpenShift Container Platform and Red Hat OpenStack Platform

The relationship between Red Hat OpenShift Container Platform (RHOCP) and Red Hat OpenStack Platform (RHOSP) is complementary. RHOSP exposes resources through its Application Programming Interface (API) and RHOCP requests those resources.

RHOSP provides RHOCP with compute, storage, and networking infrastructure, plus additional resources such as self-service load balancers and encryption.

RHOCP runs its containerized applications on the infrastructure provisioned by RHOSP. The products are tightly integrated, allowing RHOCP to consume RHOSP resources on demand and without user intervention.

3.3.1. Introducing Red Hat Enterprise Linux (RHEL) CoreOS

RHOCP 4 nodes run on Red Hat Enterprise Linux CoreOS (RHCOS). RHCOS provides over-the-air updates on a Red Hat Enterprise Linux (RHEL) kernel to deliver a secure, easily managed container host. In an installer-provisioned infrastructure deployment, and for this reference architecture, RHCOS is the supported operating system for all the RHOCP nodes, and is used by default for worker and master nodes. It is also a RHOCP requirement that the master nodes run RHCOS.


RHCOS is currently only used with RHOCP. It is not for use as an independent operating system. For more information, see CoreOS has joined the Red Hat family. Ignition

Ignition is a RHCOS utility that is used to manipulate disks during initial configuration. It completes common disk tasks, including partitioning disks, formatting partitions, writing files, and configuring users.

On first boot, Ignition reads the bootstrap configuration files, generated by the RHOCP installation program, from the OpenStack Image service.

For more information, see About Ignition.

3.4. Reference architecture high level design

This reference architecture is for the following products:

Table 3.1. Reference architecture products

ProductVersion used to test the deployment

Red Hat OpenStack Platform (RHOSP)

13, version used 13.0.11


16, version used 16.0.0

Red Hat OpenShift Container Platform (RHOCP)


Red Hat Ceph Storage

3.3, as deployed by director with RHOSP 13; BlueStore enabled as the OSD back end.


4, as deployed by director with RHOSP 16.0; BlueStore is the default OSD back end.

The following diagram provides a high level overview of the reference architecture.

Reference architecture high level design

The following table describes the components of this reference architecture.

Table 3.2. Reference architecture components


Object storage

Red Hat Ceph Object Gateway (RGW) (replaces the default OpenStack Object Storage (swift))

Block storage

Red Hat OpenStack Block Storage (cinder) backed by Red Hat Ceph Block Devices (RBD)

Image storage

Red Hat OpenStack Image Service (glance) backed by Red Hat Ceph Block Devices (RBD)

Compute service

Red Hat OpenStack Compute (nova) backed by Red Hat Ceph Block Devices (RBD)

Networking service - OpenStack

Red Hat OpenStack Networking with Open vSwitch (OVS)

Networking service - OpenShift

Red Hat OpenShift software-defined networking (SDN)


Red Hat Enterprise Linux CoreOS (RHCOS) tool, used in the Red Hat OpenShift installation process

Key reference architecture features

  • The reference architecture uses TLS for external endpoint encryption.
  • A public, external network with routable IPs in a floating IP pool is available to all tenants.
  • The default network policy mode is implemented for OpenShift SDN.
  • You have administrative access to a DNS zone to host the required domains.

Red Hat OpenShift Container Platform deployment

RHOCP does not require administrative access to the RHOSP cloud. The RHOSP administrator prepares a suitable tenant for RHOCP. RHOCP is deployed by that tenant on a RHOSP instance that is running Red Hat Enterprise Linux CoreOS (RHCOS).

This reference architecture deploys RHOCP on instances that run the RHCOS operating system installed from a RAW image.

The Ignition installation files, generated by the installation program for creating the bootstrap node, are stored in the Red Hat OpenStack Image Service (glance). The RHOCP bootstrap node requires external DNS resolution and external Internet access to set up the RHOCP cluster.