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Chapter 5. Architecture models
Red Hat OpenShift Service on AWS (ROSA) has the following cluster topologies:
- Hosted control plane (HCP) - The control plane is hosted in a Red Hat account and the worker nodes are deployed in the customer’s AWS account.
- Classic - The control plane and the worker nodes are deployed in the customer’s AWS account.
5.1. Comparing ROSA with HCP and ROSA Classic
| | Hosted Control Plane (HCP) | Classic |
|---|---|---|
| Control plane hosting | Control plane components, such as the API server etcd database, are hosted in a Red Hat-owned AWS account. | Control plane components, such as the API server etcd database, are hosted in a customer-owned AWS account. |
| Virtual Private Cloud (VPC) | Worker nodes communicate with the control plane over AWS PrivateLink. | Worker nodes and control plane nodes are deployed in the customer’s VPC. |
| Multi-zone deployment | The control plane is always deployed across multiple availability zones (AZs). | The control plane can be deployed within a single AZ or across multiple AZs. |
| Machine pools | Each machine pool is deployed in a single AZ (private subnet). | Machine pools can be deployed in single AZ or across multiple AZs. |
| Infrastructure nodes | Does not use any dedicated infrastructure nodes to host platform components, such as ingress and image registry. | Uses 2 (single-AZ) or 3 (multi-AZ) dedicated infrastructure nodes to host platform components. |
| OpenShift capabilities | Platform monitoring, image registry, and the ingress controller are deployed in the worker nodes. | Platform monitoring, image registry, and the ingress controller are deployed in the dedicated infrastructure nodes. |
| Cluster upgrades | The control plane and each machine pool can be upgraded separately. | The entire cluster must be upgraded at the same time. |
| Minimum EC2 footprint | 2 EC2 instances are needed to create a cluster. | 7 (single-AZ) or 9 (multi-AZ) EC2 instances are needed to create a cluster. |
Additional resources
5.2. ROSA with HCP architecture
In Red Hat OpenShift Service on AWS, the ROSA service hosts a highly-available, single-tenant OpenShift control plane. The hosted control plane is deployed across 3 availability zones with 2 API server instances and 3 etcd instances.
You can create a ROSA with HCP cluster with or without an internet-facing API server, with the latter considered a “private” cluster and the former considered a “public” cluster. Private API servers are only accessible from your VPC subnets. You access the hosted control plane through an AWS PrivateLink endpoint regardless of API privacy.
The worker nodes are deployed in your AWS account and run on your VPC private subnets. You can add additional private subnets from one or more availability zones to ensure high availability. Worker nodes are shared by OpenShift components and applications. OpenShift components such as the ingress controller, image registry, and monitoring are deployed on the worker nodes hosted on your VPC.
Figure 5.1. ROSA with HCP architecture
5.2.1. ROSA with HCP architecture on public and private networks
With ROSA with HCP, you can create your clusters on public or private networks. The following images depict the architecture of both public and private networks.
Figure 5.2. ROSA with HCP deployed on a public network
Figure 5.3. ROSA with HCP deployed on a private network
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