Kubernetes Interview Questions and Answers

CrashLoopBackOff means the container starts, exits, and Kubernetes restarts it with exponential backoff.

1. Get the state and previous logs.

kubectl get pod web-1 -o wide
kubectl describe pod web-1
kubectl logs web-1 --previous

1. Read the exit code: 1 is an application error, 137 is OOMKilled, and 127 is command not found.

1. Common causes:

• Application config or missing environment variables and Secrets.
• Failing readiness or liveness probes causing restarts.
• Out-of-memory: raise limits or fix a leak.
• Permission errors on mounted volumes.
• A wrong entrypoint or command.

1. Debug interactively by overriding the command, then exec in and reproduce.

1. Check events with kubectl get events --sort-by=.lastTimestamp and inspect the failing dependency.

Fix the root cause rather than only increasing the restart backoff.

The control plane maintains desired state and schedules workloads.

• kube-apiserver: the front door. It validates and persists objects to etcd, and all components talk to it.
• etcd: the consistent key-value store holding cluster state. Back it up; it is the source of truth.
• kube-scheduler: watches for unscheduled Pods and picks a node based on resource requests, affinity, taints, and topology.
• kube-controller-manager: runs controllers such as Deployment, ReplicaSet, Node, and Job that reconcile actual state toward desired state.
• cloud-controller-manager: integrates with the cloud provider for load balancers, routes, and nodes.

On each node:

• kubelet starts and monitors containers and reports status.
• kube-proxy implements Service networking.
• The container runtime pulls images and runs containers via CRI.

Flow: you apply a Deployment, the API server stores it, the Deployment controller creates a ReplicaSet, the scheduler assigns Pods to nodes, and kubelets start them.