fix(chart): topology-gate single-replica PDBs so single-node installs stay drainable (#560)

[shujaatTracebloc]

Problem

client/templates/jobs-manager-pdb.yaml and client/templates/mysql-pdb.yaml rendered minAvailable: 1 unconditionally (gated only on podDisruptionBudget.*.create, default true). For a single-replica workload, minAvailable: 1 means the eviction API permits zero voluntary disruptions (currentHealthy 1 − 1 = 0 < 1), so kubectl drain/cordon blocks forever. On a single-node install this wedges all node maintenance (manual k3s upgrade, node drain), and the pod has nowhere to reschedule anyway.

Fix — topology-gated tri-state create

The chart already distinguishes topologies via hostPath.enabled (true = single-node/bare-metal installer; false = multi-node CSI: AKS/EKS/OpenShift) — the "storage/topology mode" the issue calls for, and the same signal SINGLE_NODE already defaults from.

podDisruptionBudget.{mysql,jobsManager}.create becomes tri-state:

• null (default) = AUTO: render on multi-node CSI (hostPath.enabled=false), skip on single-node/bare-metal (hostPath.enabled=true)
• true = force render regardless of topology
• false = never render

Rationale for gating (vs maxUnavailable: 1 or a blanket off)

On multi-node CSI the PDB is a feature: it blocks a surprise autoscaler scale-down / node upgrade from silently evicting the only mysql/jobs-manager pod, forcing a deliberate operator drain of the single-replica stateful workload. Switching to maxUnavailable: 1 there would make it a no-op, and would also require rewriting the existing minAvailable-asserting unittest. On single-node the same PDB has no upside (nowhere to reschedule) and only wedges drains — so it is skipped. Topology-gating preserves the multi-node protection, keeps single-node drainable, and adds no existing-test rewrites. Default topology is CSI (hostPath.enabled=false), so default behavior is unchanged.

Changes

• client/templates/jobs-manager-pdb.yaml, client/templates/mysql-pdb.yaml — topology-gated guard; minAvailable: 1 retained where it renders.
• client/values.yaml — create: true → create: null with tri-state docs.
• client/values.schema.json — create type boolean → ["boolean","null"], default null.
• client/Chart.yaml — version/appVersion 1.9.39 → 1.9.40 (chart-version-guard, lockstep).
• client/tests/priority_class_pdb_test.yaml — added 7 cases (single-node skip, CSI render, force-on/off overrides); all existing tests kept.

Verification

• helm lint --strict — green on aks/bm/eks/oc profiles.
• helm template — renders on all 4; PDB docs: aks/eks/oc = 2, bm = 0.
• helm unittest — 7 new PDB tests pass; the local 5 failed / 5 errored are a pre-existing helm v4.2.0 schema-message artifact (identical on clean develop); CI pins helm-unittest 0.5.2.

Closes #560

🤖 Generated with Claude Code

---

Note

Medium Risk
Changes cluster maintenance behavior for PDBs on single-node vs multi-node topologies; mis-detection could drop drain protection on CSI fleets or reintroduce stuck drains on single-node installs.

Overview
Fixes #560: unconditional minAvailable: 1 PDBs on single-replica mysql and jobs-manager made kubectl drain hang forever on one-node clusters where the pod cannot reschedule.

podDisruptionBudget.{mysql,jobsManager}.create is now tri-state (null / true / false), default null (AUTO). In AUTO mode, PDBs render only on multi-node CSI (hostPath.enabled=false, typical AKS/EKS/OpenShift) and are omitted on single-node installs (hostPath.enabled=true or explicit env.SINGLE_NODE="true", matching jobs-manager’s SINGLE_NODE resolution). true / false still force render or disable regardless of topology. Where they render, minAvailable: 1 is unchanged.

Defaults move from create: true to create: null in values.yaml; the JSON schema allows boolean | null. Chart version bumps to 1.9.43. Helm unit tests cover AUTO skip/render, SINGLE_NODE edge cases, and explicit overrides.

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PDB gate misuses SINGLE_NODE flag

Medium Severity

AUTO mode treats env.SINGLE_NODE=true as single-node topology and skips the minAvailable:1 PDBs. That flag only gates GPU-to-CPU fallback and is documented for multi-node NFS/CSI clusters with hostPath.enabled=false. Those clusters lose eviction protection on auto-upgrade even though pods can reschedule.

Additional Locations (1)

• client/templates/mysql-pdb.yaml#L25-L27

 

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