Multi-stage builds with a minimal base image like Alpine are a best practice for creating small, secure final images. The builder stage can contain compilers and build tools, while the final stage contains only the runtime necessities and the compiled artifact, minimizing attack surface and size. Option A leaves unnecessary files, Option C is often impractical for complex apps, and Option D doesn’t minimize size as effectively as a multi-stage Alpine build.

To pull images from a private registry, you must create a Secret of type `kubernetes.io/dockerconfigjson` (or the older `docker-registry`). This secret holds the authentication credentials. The pod specification then references this secret in its `imagePullSecrets` field. ServiceAccounts control API access, not registry access. ConfigMaps and environment variables are not the standard, secure method for registry credentials.

`kubectl describe pod` is the most targeted first step. It provides a detailed view of the specific pod’s state, including recent events (like ‘FailedScheduling’), which will directly state the reason (e.g., ‘Insufficient cpu’, ‘node-selector mismatch’). While `kubectl get events` shows cluster events, it’s broader. `kubectl describe nodes` shows node conditions, and `kubectl logs` only works for running pods.

The `maxUnavailable` field controls how many pods can be unavailable during the update. If set to 0 (or a low percentage), the rolling update will wait for a new pod to become `Ready` (passing its readiness probe) before terminating an old one. This ensures service capacity is maintained. `maxSurge` controls how many extra pods can be created. `progressDeadlineSeconds` marks a deployment as failed, and `minReadySeconds` ensures a pod is stable before being considered ready.

A Job is the Kubernetes resource designed specifically for running finite, completion-based tasks. Setting `spec.parallelism: 5` tells the Job controller to create up to 5 Pods to run the job logic concurrently. The controller will ensure the job runs to completion and then clean up the pods. Deployments and StatefulSets are for long-running services, and manually creating multiple Pods lacks the management and completion tracking of a Job.

An `emptyDir` volume is created when a Pod is assigned to a node and exists as long as that Pod is running on that node. It is a perfect, simple mechanism for sharing files between containers in the same pod. The containers can mount the `emptyDir` at different paths. `hostPath` is for node-specific files and is not ideal for inter-container sharing. `persistentVolumeClaim` is for persistent storage beyond the pod’s lifecycle. `configMap` is for read-only configuration data.

The `initialDelaySeconds` field specifies the number of seconds to wait after the container has started before initiating the first liveness or readiness probe. This is crucial for applications that have a significant startup time. Increasing this value prevents the kubelet from killing a container that is still in its initialization phase. The other options control probe execution (`periodSeconds`), timeout for each attempt (`timeoutSeconds`), and how many consecutive failures are allowed (`failureThreshold`).

Both option C (`nodeSelector`) and option D (Node Affinity) can achieve this. However, the question asks for the requirement to be expressed in the pod spec. Node Affinity (option D) is the more expressive and modern method, allowing for complex rules. `requiredDuringSchedulingIgnoredDuringExecution` makes it a hard requirement. While `nodeSelector` (option C) would also work, node affinity is its functional successor and is considered a best practice for such constraints. `nodeName` bypasses scheduling, and `tolerations` are for accepting taints, not selecting labels.

A ConfigMap is specifically designed to decouple configuration artifacts from container images, allowing you to change configuration without rebuilding the image. When a ConfigMap mounted as a volume is updated, the files in the mounted volume are eventually updated for running pods. Secrets are for sensitive data. PersistentVolumes are for persistent storage, and the Downward API is for exposing pod/container metadata, not arbitrary configuration files.

Multi-stage builds with a minimal base image like Alpine are a best practice for creating small, secure final images. The builder stage can contain compilers and build tools, while the final stage contains only the runtime necessities and the compiled artifact, minimizing attack surface and size. Option A leaves unnecessary files, Option C is often impractical for complex apps, and Option D doesn’t minimize size as effectively as a multi-stage Alpine build.0