Study notes · 10% of the exam

Pods and Workload Controllers

Know how Pods work and which controller to use for each workload, and how restarts, probes, termination and Job/CronJob semantics behave in practice.

Key points

1
A Pod is the smallest unit: its containers share one network namespace (localhost, one IP) and any mounted volumes. Pods are ephemeral and not self-healing; controllers replace them.
2
Pick the controller by shape: Deployment (stateless replicas, rolling updates via ReplicaSets), StatefulSet (ordinal names, stable DNS via a headless Service, per-Pod storage), DaemonSet (one per eligible node), Job/CronJob (run to completion, on a schedule).
3
Probes: readiness gates traffic, liveness restarts the container, and a startup probe suspends both until the app has started (budget = failureThreshold × periodSeconds). Keep liveness checks to the process itself.
4
Restarts back off 10s, 20s, 40s… up to 300 s (CrashLoopBackOff) and reset after 10 minutes of healthy running. OOMKilled with exit code 137 means the memory limit was hit.
5
Termination: deletion timestamp → (in parallel) endpoint removal and preStop → SIGTERM → SIGKILL after terminationGracePeriodSeconds (default 30). A short preStop sleep avoids dropped requests.
6
Jobs: completions vs parallelism, backoffLimit (default 6), activeDeadlineSeconds takes precedence, Indexed mode gives each Pod JOB_COMPLETION_INDEX, and podFailurePolicy (first match wins, needs restartPolicy Never).
7
Native sidecars (initContainers with restartPolicy: Always, stable since 1.33) start before the app, keep running, support probes, stop after the main containers, and do not block Job completion.

A liveness probe that checks the database turns a database blip into restart storms across every replica.
Rolling back to revision 2 renumbers it as the newest revision; revision 2 disappears from rollout history.
Bare Pods whose labels match a controller's selector get adopted (or deleted as surplus), and overlapping selectors between controllers cause unpredictable fights.

Ten questions, with the answer and explanation after each one.