While all options are important, the `name` field for a container is mandatory in the Kubernetes API. A Pod spec with a container missing a `name` will fail validation and cannot be scheduled. Other fields like `restartPolicy` have defaults, and `command` or `resources` are optional for basic functionality.

CoreDNS (or kube-dns) is the cluster’s internal DNS server responsible for resolving Service names. If its Pods are not running or healthy, internal DNS resolution will fail. Checking its status is the most direct first step. While kubelet and network policies can affect networking, they are less specific to a pure DNS failure, and the `clusterIP` is irrelevant if the DNS service itself is down.

The core idea of declarative management is that the manifest file is the source of truth. An imperative edit changes the live object but not the source file. A subsequent `kubectl apply` will reconcile the live state with the file, likely overwriting the manual change. This leads to configuration drift and unpredictability.

Using `kubectl apply` with a manifest is the declarative and idempotent best practice. It will create the namespace if it doesn’t exist, and do nothing (successfully) if it does. Option A (`create`) will fail if the namespace already exists. Options C and D are imperative scripts that work but are less clean and not purely declarative.

Linkerd is a graduated CNCF project that is a lightweight service mesh. A service mesh is a dedicated infrastructure layer for handling service-to-service communication, providing features like traffic management, observability, and security. Envoy is a proxy often *used within* a service mesh (like Istio), but is not the mesh itself. Prometheus is for monitoring, and Helm is for packaging.

The kube-controller-manager runs control loops, including the node controller. One of its jobs is to monitor node health. When a node fails its health checks for a prolonged period (the pod-eviction-timeout), the node controller marks it as unready and triggers the deletion of the Pods assigned to it. Once the Pods are deleted, the scheduler (kube-scheduler) will assign them to new nodes.

The core promise of containerization is consistency and portability across environments. By bundling the app, runtime, system tools, libraries, and settings, the container image becomes a self-contained, predictable unit. This eliminates the classic “it works on my machine” problem, as the same image runs identically on any compatible container host.

A restart policy of `OnFailure` means the kubelet will restart a container only if it terminates with a non-zero exit code (i.e., it fails). An exit code of 0 indicates successful completion. For a Pod with a single container that succeeds, the Pod’s status will become `Succeeded` (or `Completed`), and the container will not restart.

At its heart, GitOps is an operational model that uses Git as the single source of truth for declarative infrastructure and applications. A Git repository stores the desired state (manifests), and an automated agent (like Flux or ArgoCD) continuously reconciles the live state in the cluster with the state defined in Git. While using Git for source code and PR reviews are common, they are not the unique, defining element.

While all options are important, the `name` field for a container is mandatory in the Kubernetes API. A Pod spec with a container missing a `name` will fail validation and cannot be scheduled. Other fields like `restartPolicy` have defaults, and `command` or `resources` are optional for basic functionality.0