Document the design of Adaptable Topology, a new cluster topology mode that enables OpenShift clusters to dynamically scale from single-node to highly-available multi-node configurations without redeployment.

Adaptable topology adjusts cluster control-plane and infrastructure behavior based on the current number of control-plane and worker nodes, enabling edge deployments to start small and grow as needed.

Acceptance Criteria

• Research spikes completed and closed
• Enhancement proposal approved and merged: https://github.com/openshift/enhancements/pull/1905

Scope

In Scope

• Infrastructure Config API extensions with AdaptableTopology feature gate
• cluster-etcd-operator updates for safe quorum management during transitions
• Core payload operator compatibility and behavior updates
• OLM operator compatibility annotation framework
• Shared library-go utilities for topology detection
• Comprehensive testing strategy across scaling scenarios
• Documentation for cluster administrators and operator authors

Out of Scope

• AutomaticQuorumRecovery (AQR) implementation (future enhancement)
• Bidirectional topology transitions (only one-way: SingleReplica → Adaptable)
• Automatic node provisioning
• HyperShift or MicroShift cluster support
• HighlyAvailable → Adaptable transitions (focus on SNO use case)

Timeline

• Target: OpenShift 4.22

Additional Context

• Enhancement Proposal: https://github.com/openshift/enhancements/pull/1905