PV, PVC and Binding

A PersistentVolume represents storage capacity; a PersistentVolumeClaim requests capacity, access mode and class. Binding is normally one-to-one. Access modes describe mount capabilities, not application-level concurrency guarantees. ReclaimPolicy determines what happens to the backing asset after claim deletion.

Analogy: Kubernetes is a thermostat, not a remote control. You declare the temperature; independent controllers measure reality and keep acting. Debugging means finding which sensor, rule or actuator prevents convergence.

Read the object as evidence

kubectl get RESOURCE NAME -n NAMESPACE -o yaml
kubectl describe RESOURCE NAME -n NAMESPACE
kubectl get events -n NAMESPACE --sort-by=.metadata.creationTimestamp
kubectl explain RESOURCE.spec

Do not memorize these as a ritual. The first command exposes desired and observed state, the second connects conditions and events, the third supplies a timeline, and the fourth checks the server's schema. Compare what the controller was asked to do with what it reports doing. Then test the narrowest hypothesis.

Scenario: A PVC remains Pending because no PV or provisioner satisfies class, size, access mode and topology. Describe the claim and inspect StorageClasses and events before changing the Pod.

Debug binding as constraint matching

Describe the PVC and compare requested size, access modes, storageClassName, selector and volumeMode with available PVs or the dynamic provisioner. Then check Pod scheduling and topology. kubectl get pv,pvc shows phase, but events explain why binding or mounting failed. Read reclaim policy before deletion: Retain leaves manual recovery work; Delete may destroy the backing volume.

Scenario: A claim asks for ReadWriteMany on a block class that only supports ReadWriteOnce. Adding more PV capacity cannot satisfy an incompatible access mode; select a capable backend or redesign writers.
Scenario: A PVC is Bound but the Pod reports Multi-Attach after moving nodes. Binding succeeded; the storage attachment lifecycle is now blocked by the old node or driver.

Production reasoning

Ask four questions: Who owns this object? What dependency must become ready next? Which controller reports the blocking condition? What evidence would disprove my current theory? This prevents symptom-driven changes. Record the context, namespace, object generation, image digest and recent rollout before mutation; a recreated Pod may erase the evidence you needed.

Warning: Running is not the same as ready, healthy, durable or correct. Kubernetes status is layered. Confirm the application-level outcome as well as the object state.
Goal: Put this model into practice in the Kubernetes lab pvc-storageclass-binding. Open /labs/kubernetes, choose pvc-storageclass-binding, predict the failure path before changing anything, then use the simulator's check command to validate the finished state.

Deliberate practice

Before the lab, write the expected object relationship and the first three commands you will run. Afterward, explain why the fix converged and name one tempting change that would only mask the symptom. Repeat using an explicit namespace and a structured output format. This prediction-observation-explanation loop is what turns command familiarity into production judgment.

45-minute investigation

  1. Map (5 min): draw the owner-to-child chain and mark every namespace, selector, identity and dependency involved.
  2. Predict (5 min): write one expected status condition, one likely event and one log or metric signal before opening the lab.
  3. Observe (10 min): collect YAML, describe output and ordered events. Do not mutate state. Record which observation disproves your first theory.
  4. Repair (15 min): make the smallest declarative correction, watch the responsible controller converge, and verify the user-facing path rather than stopping at Running.
  5. Stress (10 min): change one relevant constraint - replica count, label, readiness, resource value or placement rule - predict the outcome, observe it, then restore the known-good declaration.
Tip: Keep a short incident note with symptom, evidence, hypothesis, change, result. Across four sections this produces a reusable runbook instead of a pile of remembered commands.