architecture_design.md

Cluster API OpenShift Agent providers Architecture Design

Overview

OpenShift Agent providers are a pair of CAPI providers, bootstrap and control plane, which objective is to install OpenShift on BareMetal.

Goals

• Install OpenShift on BareMetal without the need of a Bootstrap Node
• Adheres to cluster API contracts (whenever possible)

Non-goals

• Install OpenShift on cloud provider platforms

Supported infrastracture providers

• CAPM3

Components

Agent Bootstrap Provider

Description

The Agent Bootstrap (AB) provider controller is responsible for generating a live ISO for each machine, interacting with assisted installer to install nodes.

Custom Resources

TODO: if possible, generate from openapi CRDs below

• OpenshiftAssistedConfig
• OpenshiftAssistedConfigTemplate

Flow

AB watches OpenshiftAssistedConfig, Machines, InfraEnvs and Agents resources

• creates an InfraEnv resource for each OpenshiftAssistedConfig and passes the LiveISOURL to the Machine's InfrastructureReference (Metal3Machine)
  • 1 infraenv each metal3machinetemplate
• add iso to template (we need to make sure machine don't escape)
• create BootstrapData secret (empty), to allow machine to boot
• sets Agent's role
• set node providerID label
• approves Agents
• notifies core CAPI components that the machine is ready (setting status.Ready)

Agent Control Plane Provider

Description

The Agent Control Plane (ACP) provider is responsible for orchestrating the cluster installation through assisted installer and relay the control plane status back to CAPI core components.

Custom Resources

TODO: if possible, generate from openapi CRDs below

• OpenshiftAssistedControlPlane

Flow

ACP watches OpenshiftAssistedControlPlane, ClusterDeployment, AgentClusterInstall

• creates ClusterDeployment
• creates AgentClusterInstall (ACI) and sets control plane and workers number of replicas, according to what's defined in CAPI core components
• creates Machines and OpenshiftAssistedConfigs for the control plane
• once ACI installs successfully, it creates a kubeconfig secret and sets status' Initialized and Ready for CAPI core components to read

Notes

• The first installation will be performed as day-1 (master+workers at the same time)
• All nodes added after the first installation, they will be added as day-2 nodes
• AB controller will prevent Machines from installing when an installation is in progress. Once the installation completes, they will be added

Future work

• Leverage use qcow2 instead of live-iso from assisted

Remove this: TODO: global flow/diagram section?