feat(clusters): enforce PayloadSchedulable condition for workerless clusters

[Zaggy21]

Description

Introduces ClusterMode (Default/Workerless) to the Cluster API and wires it through the cluster and plugin controllers to prevent Helm releases from being deployed to clusters that cannot schedule workloads.

When a Cluster secret has the greenhouse.sap/workerless annotation, the bootstrap controller sets spec.mode=Workerless on the Cluster. The cluster controller then sets PayloadSchedulable=False on that cluster and skips the AllNodesReady condition, since workerless clusters have no worker nodes. Finally, the plugin controller checks PayloadSchedulable before deploying a Helm release and blocks deployment if it is False.

The greenhouse.sap/workerless annotation on the Cluster secret is set by shoot-grafter in cloudoperators/shoot-grafter#79.

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation Update
• 🎨 Style
• 🧑‍💻 Code Refactor
• 🔥 Performance Improvements
• ✅ Test
• 🤖 Build
• 🔁 CI
• 📦 Chore (Release)
• ⏩ Revert

Related Tickets & Documents

• Closes [FEAT] - Enforce PayloadSchedulable condition check in Plugin controller #1967

Added tests?

• 👍 yes
• 🙅 no, because they aren't needed
• 🙋 no, because I need help
• Separate ticket for tests # (issue/pr)

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Added to documentation?

• 📜 README.md
• 🤝 Documentation pages updated
• 🙅 no documentation needed
• (if applicable) generated OpenAPI docs for CRD changes

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

[Copilot]

🟡 Changes recommended

The bootstrap controller currently forces spec.mode back to Default when the workerless annotation is absent, which can unintentionally override an explicitly set Workerless mode and undermine the safety behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds an explicit “workerless” cluster mode to prevent deploying plugin workloads onto clusters that cannot schedule them (e.g., Gardener etcd-only shoots), by driving cluster conditions and gating plugin reconciliation on those conditions.

Changes:

• Introduces ClusterSpec.Mode (Default / Workerless) and exposes it via the Cluster CRD.
• Updates cluster reconciliation phases to (a) remove AllNodesReady/Status.Nodes for workerless clusters and (b) set PayloadSchedulable=False with a workerless-specific reason.
• Updates plugin reconciliation (initClientGetter) to block Helm release creation when the target cluster’s PayloadSchedulable is False, and adds unit tests for the new gating behavior.

File summaries

File	Description
api/v1alpha1/cluster_types.go	Adds ClusterMode enum, spec.mode, and WorkerlessClusterReason.
charts/manager/crds/greenhouse.sap_clusters.yaml	Extends CRD schema with spec.mode (enum + default).
api/well_known.go	Adds greenhouse.sap/workerless annotation constant for secrets.
internal/controller/cluster/bootstrap_controller.go	Sets cluster.spec.mode based on the secret annotation.
internal/controller/cluster/phases/ensure_nodes_ready.go	Skips node readiness condition/status for workerless clusters.
internal/controller/cluster/phases/ensure_workload_schedulable.go	Forces PayloadSchedulable=False for workerless clusters.
internal/controller/cluster/phases/phases_test.go	Adds unit tests for workerless phase behavior.
internal/controller/plugin/util.go	Blocks client init / Helm release creation when PayloadSchedulable=False.
internal/controller/plugin/util_test.go	Adds unit tests for the new PayloadSchedulable gating.
api/v1alpha1/plugin_types.go	Adds ClusterPayloadNotSchedulableReason for plugin condition reporting.
pkg/mocks/mock_Reconciler.go	Import alias adjustment for controller-runtime in generated mocks.

Review details

Files not reviewed (1)

• pkg/mocks/mock_Reconciler.go: Generated file

• Files reviewed: 12/13 changed files
• Comments generated: 1
• Review effort level: Lite

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