Volume Types

Ephemeral Versus Durable

Pod storage splits into two lifetimes. Ephemeral volumes live exactly as long as the pod: emptyDir (node disk, or memory with medium: Memory), configMap/secret/projected for read-only config, and the container's own log directory. They vanish on pod deletion and do not follow a rescheduled pod to a new node.

Durable storage belongs to the persistent family (PVCs, covered next), plus hostPath, which pins a node path into the pod.

volumes:
- name: scratch
  emptyDir: { sizeLimit: 2Gi }
- name: cache
  emptyDir: { medium: Memory, sizeLimit: 512Mi }

sizeLimit with ephemeral-storage limits stops a noisy container from filling the node's disk.

hostPath Types and Projections

hostPath mounts a node file or directory; its type controls what happens when the path is missing:

volumes:
- name: podlogs
  hostPath: { path: /var/log/pods, type: Directory }
- name: combined
  projected:
    sources:
    - configMap: { name: app-config }
    - secret: { name: db-creds }

hostPath couples pods to one node — correct for node agents, wrong for general workloads. Projected volumes merge several sources into a single mount with unified refresh.

Pitfalls and Interview Angles

Pitfall 1 — emptyDir as a database. Data dies with the pod and competes with image layers for node disk; node pressure then triggers evictions. Durable state belongs on a PVC.

Pitfall 2 — unrestricted hostPath. Mounting / or the container runtime socket hands the pod node control — which is exactly why Pod Security Standards restrict hostPath.

Interview-ready: sort a workload's data by lifetime (scratch = emptyDir, config = projected, state = PVC), cite medium: Memory as swap-free cache with sizeLimit, and explain why hostPath appears only in node-level DaemonSets.