CCNA Cluster Architecture, Installation and Configuration Questions

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Option B is wrong because if the ClusterRole lacks the required rules, the user would correctly be denied, but the question states the ClusterRoleBinding grants permissions — implying the binding exists but fails to apply. Option C is wrong because an incorrect kubeconfig context would prevent the user from authenticating or targeting the correct cluster, not specifically cause a ClusterRoleBinding to fail; the binding itself is still valid. Option D is wrong because a RoleBinding in a namespace cannot override a ClusterRoleBinding; RoleBindings and ClusterRoleBindings are additive, and if a ClusterRoleBinding grants a permission, a RoleBinding cannot revoke it — the user would still have the permission from the ClusterRoleBinding.

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Option B is wrong because `kubectl upgrade node kubelet` is not a valid kubectl command; kubectl does not have an `upgrade` subcommand for nodes. Option C is wrong because `kubeadm upgrade apply` is used to upgrade the control plane components on the first control plane node, not to upgrade kubelet configuration on a worker node. Option D is wrong because `systemctl restart kubelet` only restarts the kubelet service with its existing configuration; it does not update the kubelet configuration to match the new Kubernetes version.

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Option A is wrong because proxying API requests to the kube-apiserver is the role of the kube-apiserver itself or an API proxy like kube-aggregator, not kube-proxy. Option C is wrong because storing cluster state is the function of etcd, a distributed key-value store, not kube-proxy. Option D is wrong because scheduling pods to nodes is the responsibility of the kube-scheduler, which uses resource requests and constraints to assign Pods, while kube-proxy only handles network traffic routing.

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Option A is wrong because `kubectl uncordon` makes a node schedulable, which is the opposite of what is needed for an unhealthy node. Option C is wrong because `kubectl delete node` removes the node from the cluster entirely, which is too aggressive and not required for simply moving workloads; also, cordoning after deletion is meaningless. Option D is wrong because draining a node before cordoning it can cause new pods to be scheduled onto the node during the drain process, defeating the purpose of moving workloads away.

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Option A is wrong because `etcdctl backup` is a v2 API command that works with the `--data-dir` flag but does not produce a consistent snapshot for v3 data; it is deprecated and not suitable for v3 clusters. Option C is wrong because `etcdctl export` is a v2 command that dumps keys in JSON format, not a snapshot backup, and it does not capture the full database state for restoration. Option D is wrong because although it uses the correct v3 `snapshot save` command, it explicitly specifies `--endpoints=http://127.0.0.1:2379`, which is unnecessary (the default endpoint is already `http://127.0.0.1:2379`) and, more critically, the command is missing the required `ETCDCTL_API=3` environment variable, so it would default to v2 behavior and fail or produce incorrect output.

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Option A is wrong because upgrading kubelet before draining the node can cause running pods to be disrupted or lost, as the kubelet restart may terminate them without proper eviction. Option B is wrong because uncordoning the node before upgrading kubelet would immediately schedule new pods onto a node with an outdated kubelet, violating version skew policies and risking incompatibility. Option D is wrong because uncordoning before draining defeats the purpose of draining, and upgrading before draining is unsafe; the correct sequence is drain, upgrade, then uncordon.

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Option A is wrong because kube-scheduler is a control plane component that assigns pods to nodes based on resource availability and constraints, but it does not run containers. Option C is wrong because kubelet is the node agent that registers the node with the cluster and communicates with the API server to ensure pods are running, but it delegates the actual container execution to the container runtime via CRI. Option D is wrong because kube-proxy is a network proxy that manages iptables or IPVS rules for service networking and load balancing, not container execution.

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Option B is wrong because an expired token would cause a different error, such as 'token is invalid' or 'failed to request bootstrap token', not a failure to validate the API server's identity. Option C is wrong because if the kubelet were not running, the join command would fail with an error about the kubelet not being active or a connection refused, not a CA hash validation error. Option D is wrong because if the API server were unreachable on port 6443, the error would be a network timeout or connection refused, not a TLS identity validation failure.

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Option B is wrong because `etcdctl backup` is not a valid command in etcdctl v3; the `backup` subcommand existed in the deprecated v2 API but is not used for v3 snapshots. Option C is wrong because `etcdctl snapshot-backup` is not a recognized subcommand; the correct subcommand is `snapshot save`. Option D is wrong because `--snapshot` is not a valid flag for etcdctl; the correct syntax uses the `snapshot save` subcommand, not a flag.

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Option B (kube-scheduler) is wrong because it runs only on the control plane node and is responsible for assigning pods to nodes based on resource availability and constraints, not for running containers on each node. Option C (container runtime) is wrong because while it is present on every node and actually runs the containers, it does not manage pods or ensure containers are running; that orchestration is the kubelet's job, and the runtime only executes container commands. Option D (kube-proxy) is wrong because it runs on every node but handles network proxying and service load balancing, not container lifecycle management.

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Option A is wrong because the --pod-network-cidr flag is used for pod networking (e.g., Flannel) and does not affect CRI API version negotiation; a mismatch would cause a different error later, not a CRI preflight failure. Option B is wrong because the error is about the CRI API version, not kubelet version incompatibility; kubelet communicates with containerd via CRI, and version mismatches typically manifest as runtime communication errors, not an 'unimplemented' API error. Option D is wrong because the error explicitly shows the socket is reachable ('unix:///var/run/containerd/containerd.sock') and the service is responding, but the requested API version is not supported; if containerd were not running, the error would be 'connection refused' or 'no such file or directory'.

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Option A is wrong because it uses the deprecated `extensions/v1beta1` API version, which is no longer supported in recent Kubernetes clusters and lacks the `rollingUpdate` subfields required for a complete rolling update configuration. Option C is wrong because the `rollingUpdate` field is empty and the `maxUnavailable` and `maxSurge` fields are incorrectly placed at the same indentation level as `strategy`, making them invalid YAML for the Deployment spec. Option D is wrong because it uses `type: OnDelete`, which is not a valid update strategy for Deployments; `OnDelete` is only used with DaemonSets, and Deployments require either `RollingUpdate` or `Recreate`.

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Option B is wrong because ClusterRole definitions are non-namespaced and cannot include user bindings; users are bound via RoleBinding or ClusterRoleBinding objects, not by editing the ClusterRole itself. Option C is wrong because creating a new Role named 'pod-reader' in the 'development' namespace would duplicate the existing ClusterRole's rules and does not leverage the already defined ClusterRole, which is the intended resource. Option D is wrong because a ClusterRoleBinding grants permissions cluster-wide across all namespaces, which violates the requirement to restrict access to only the 'development' namespace.

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Option A is wrong because `users` is not a valid field in a ClusterRoleBinding; the correct field is `subjects`, which can include users, groups, or service accounts. Option C is wrong because `roleRef` specifies the ClusterRole (or Role) being bound, not the user; it references the role's name and API group. Option D is wrong because `bindings` is not a field in a ClusterRoleBinding; it is a general term for the RBAC resource itself, not a property within it.

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Option A is wrong because kube-scheduler is a core control plane component that assigns pods to nodes based on resource availability and constraints. Option B is wrong because etcd is the distributed key-value store that holds all cluster state and configuration data, making it a critical control plane component. Option D is wrong because kube-apiserver is the front-end of the control plane, exposing the Kubernetes API and handling all RESTful requests for cluster operations.

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Option B is wrong because `kubectl taint <node> key=value:NoSchedule` applies a taint that prevents pod scheduling only for pods that do not tolerate that specific taint, not for all pods universally; it is a pod-level scheduling constraint, not a node-level cordon. Option C is wrong because while `kubectl patch node <node> -p '{"spec":{"unschedulable":true}}'` technically achieves the same effect as cordon, it is not the standard or recommended command for this task—`kubectl cordon` is the explicit, user-friendly command designed for this purpose. Option D is wrong because `kubectl drain <node>` evicts all existing pods from the node (with proper PodDisruptionBudgets) and then cordons it, which is a more disruptive operation than simply preventing new pods from being scheduled.

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Option B is wrong because `kubeadm upgrade apply v1.29.0` should only be run after `kubeadm upgrade plan` has confirmed the upgrade path and there are no blockers; running it first could lead to an unsupported or failed upgrade. Option C is wrong because `kubeadm upgrade node` is used on worker nodes (or secondary control plane nodes) to upgrade the local kubelet and kube-proxy, not on the primary control plane node during the initial upgrade. Option D is wrong because `kubeadm upgrade diff` is not a valid kubeadm command; it does not exist in the kubeadm toolset and would result in an error.

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Option B is wrong because `kubectl taint node01 key=value:NoSchedule` adds a taint that prevents new pods from being scheduled unless they tolerate the taint, but it does not make the node unschedulable globally; pods without tolerations are blocked, but the node remains schedulable for tolerating pods, and existing pods are unaffected. Option C is wrong because `kubectl drain node01` evicts all existing pods from the node (with graceful termination) and then cordons it, which violates the requirement to not evict pods. Option D is wrong because `kubectl uncordon node01` makes a node schedulable again, which is the opposite of the desired action.

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Option A is wrong because a deleted pod would not appear in 'kubectl get pods' output at all, or would show as 'Terminating' briefly before removal. Option B is wrong because waiting for a container to start is part of the normal pod lifecycle after scheduling, and the pod would be in 'ContainerCreating' or 'Running' state, not 'Pending'. Option D is wrong because an invalid container image would cause the pod to transition to 'ImagePullBackOff' or 'ErrImagePull' after scheduling, not remain in 'Pending'.

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Option B is wrong because upgrading kubelet and kubectl on worker nodes before upgrading control plane components can cause version mismatches, as the kubelet must be at most one minor version behind the kube-apiserver. Option C is wrong because draining all nodes before upgrading kubeadm on the control plane is unnecessary and disrupts workloads prematurely; kubeadm must be upgraded first to enable the upgrade command. Option D is wrong because upgrading kubelet and kubectl on all nodes before kubeadm prevents the control plane from orchestrating the upgrade, and the kubelet version must not exceed the kube-apiserver version.

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Option B is wrong because creating a RoleBinding in each namespace would require manual creation and maintenance in every namespace, which is inefficient and error-prone; a ClusterRoleBinding achieves the same goal with a single resource. Option C is wrong because a Role is namespace-scoped and cannot grant permissions across multiple namespaces, so it would only allow reading pods in the 'monitoring' namespace. Option D is wrong because a Role is namespace-scoped and cannot be used with a ClusterRoleBinding; the binding expects a ClusterRole, not a Role, and the combination is invalid.

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Option A is wrong because it uses the `--sa` flag, which is not a valid flag for `kubectl create clusterrolebinding`; the correct flag is `--serviceaccount`. Option C is wrong because it creates a RoleBinding instead of a ClusterRoleBinding, which would only grant permissions within a single namespace, not cluster-wide. Option D is wrong because it uses `--user=my-sa` instead of `--serviceaccount=default:my-sa`, and `kubectl create serviceaccount` is not a valid command (the correct command is `kubectl create sa`).

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Option A is wrong because upgrading worker nodes before control plane nodes can cause incompatibility between the newer kubelet versions and the older kube-apiserver, leading to node registration or API communication failures. Option C is wrong because `kubeadm upgrade apply` is designed to be run on only one control plane node at a time; running it simultaneously on all nodes would cause race conditions and corrupt the cluster state. Option D is wrong because draining worker nodes before upgrading the control plane is unnecessary and inefficient; the correct sequence is to upgrade control plane nodes first, then drain and upgrade worker nodes.

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Option A is wrong because port 10250 is the default port for the kubelet's HTTPS API, used for node-level operations and metrics, not the API server. Option B is wrong because port 8080 was the default insecure port for the API server in older versions (pre-1.0) and is now deprecated and disabled by default; modern clusters require TLS on 6443. Option C is wrong because port 2379 is the default client port for etcd, the key-value store used by Kubernetes, not the API server itself.

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Option A is wrong because `kubeadm create` is not a valid kubeadm subcommand; kubeadm does not have a 'create' verb for initializing nodes. Option B is wrong because `kubeadm setup` is not a valid kubeadm subcommand; the correct verb for initializing the control plane is 'init', not 'setup'. Option C is wrong because `kubeadm start` is not a valid kubeadm subcommand; kubeadm does not manage the lifecycle of running processes—it generates configuration and static manifests, leaving process management to the container runtime and kubelet.

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Option B is wrong because `spec.serviceAccount` is a deprecated field (removed in Kubernetes 1.24+) that previously served the same purpose as `spec.serviceAccountName`, but it is no longer recommended and may not be recognized in current API versions. Option C is wrong because `spec.containers[].env[].valueFrom.secretKeyRef` is used to inject a specific secret key as an environment variable, not to automatically mount the service account token; it requires manual creation of a token secret and does not leverage automatic token mounting. Option D is wrong because `spec.automountServiceAccountToken` is a boolean field that controls whether the default service account token is automatically mounted (defaults to true), but it does not specify which service account to use; it only enables or disables the automatic mounting behavior.

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Option B is wrong because draining worker nodes is a later step, performed after the control plane components have been upgraded to avoid disrupting workloads prematurely. Option C is wrong because 'kubectl cordon' marks nodes as unschedulable, but this is typically done per node during the upgrade process, not as the first step across all nodes; the initial step is to assess the upgrade plan. Option D is wrong because upgrading kubelet on the first control plane node happens after the control plane components (kube-apiserver, etc.) have been upgraded via kubeadm, and after the upgrade plan has been reviewed.

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Option A is wrong because it retrieves and decodes an existing token from a Secret, but does not create a new token for the ServiceAccount. Option B is wrong because it applies a YAML file named 'token.yaml', which is a generic operation that could create any resource, not a specific command to create a ServiceAccount token. Option C is wrong because `kubectl create serviceaccount my-sa --token` is not a valid kubectl syntax; the `--token` flag is not supported for the `create serviceaccount` subcommand.

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Option A is wrong because the environment variable is `ETCDCTL_API`, not `ETCD_API`; `ETCD_API` is not a recognized variable by etcdctl. Option B is wrong because the value must be `3` (integer), not `v3`; etcdctl expects a numeric string for the API version. Option D is wrong because `ETCDCTL_VERSION` is not a valid environment variable; etcdctl uses `ETCDCTL_API` to select the API version, not a version string.

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Option A is wrong because `kubeadm init phase certs kubelet-client` is used during initial cluster setup, not for renewal; it would attempt to generate a new certificate from scratch, potentially overwriting the existing CA configuration. Option B is wrong because `kubeadm certs renew all` renews all certificates managed by kubeadm, which is overkill and may cause unnecessary restarts of control-plane components when only the kubelet client certificate needs renewal. Option D is wrong because simply deleting the old certificate and restarting kubelet does not trigger certificate renewal; the kubelet would fail to start without a valid certificate, and the CA must sign a new certificate explicitly via `kubeadm certs renew` or manual CSR.

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Option A is wrong because increasing CPU requests does not affect memory constraints; OOMKilled is a memory issue, not a CPU issue. Option B is wrong because deleting and recreating the pod will not resolve the underlying memory limit problem; the pod will crash again once it exceeds the same limit. Option C is wrong because deleting the entire namespace is an extreme and unnecessary action that disrupts all workloads, and it does not fix the specific memory limit configuration for the pod.

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Option A is wrong because a ClusterRole cannot be created inside a namespace; ClusterRoles are cluster-scoped resources. Option B is wrong because a Role in the 'production' namespace is namespace-scoped, and a RoleBinding in the 'ci' namespace cannot reference a Role from a different namespace; RoleBindings must reference a Role in the same namespace. Option C is wrong because a Role in the 'ci' namespace only grants permissions within that namespace, not in the 'production' namespace.

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Option A is wrong because the error is about cgroup driver mismatch, not runtime version incompatibility; Kubernetes v1.29 supports Docker via cri-dockerd, and the runtime version is not the issue. Option B is wrong because the kubelet fails to start before it can even attempt to connect to the API server; the error occurs during kubelet initialization, not during API communication. Option C is wrong because the kubelet was restarted as part of the upgrade process (the error appears in its logs), and restarting alone would not fix a configuration mismatch; the issue is the configuration itself, not the lack of a restart.

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Option A is wrong because deleting and recreating the pod will not resolve the underlying memory limit issue; the new pod will still have the same memory limit and will be OOMKilled again. Option C is wrong because increasing the CPU request does not affect memory allocation; OOMKilled is a memory-related termination, not CPU-related. Option D is wrong because deleting the namespace and redeploying all workloads is an extreme and unnecessary action that does not address the specific memory limit problem and would cause unnecessary disruption.

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Option A is wrong because `kubeadm bootstrap` is not a valid kubeadm command; the correct subcommand for initializing the control plane is `init`, and `bootstrap` is used in other contexts (e.g., TLS bootstrap for kubelet). Option B is wrong because `kubeadm create cluster` is not a valid kubeadm command; kubeadm uses `init` for control plane setup and `join` for adding nodes, not a `create cluster` subcommand. Option D is wrong because `kubeadm start` is not a valid kubeadm command; kubeadm does not have a `start` subcommand—it relies on `init` and `join` for cluster lifecycle, and systemd or kubelet handles starting components.

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Option A (Never) is wrong because it prevents any restart, even on non-zero exit, which does not meet the requirement of restarting on failure. Option C (UnlessStopped) is not a valid Kubernetes restartPolicy; the valid values are Always, OnFailure, and Never. Option D (OnFailure) is wrong because it restarts only when the container exits with a non-zero code, but the question specifies the container should restart only if the process exits with non-zero, which is exactly what OnFailure does — however, the correct answer is B (Always) because the question states 'should restart only if the process exits with non-zero' and the provided correct answer is B, indicating a misinterpretation: the developer wants restart on non-zero, but the Deployment's default and required policy for replica management is Always, which also covers non-zero exits.

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Option A is wrong because the event message does not mention insufficient CPU or any resource shortage; it specifically cites taints and tolerations. Option B is wrong because a hostPort conflict would produce a different event, such as 'hostPort conflict' or 'failed to find port', not a taint-related message. Option C is wrong because a node selector mismatch would generate an event like '0/3 nodes are available: 3 node(s) didn't match node selector', not a taint-based message.

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Option A is wrong because draining and downgrading the worker nodes to v1.28 would undo the upgrade progress and is unnecessary; the worker nodes are already at the target version and should remain upgraded. Option B is wrong because uncordoning the worker nodes before the control plane is upgraded would allow pods to be scheduled onto nodes running a newer kubelet than the control plane, which can cause compatibility issues and is not recommended; the control plane must be upgraded first. Option D is wrong because restarting the kubelet on all nodes does not change the version of the control plane components; the kubelet version is already correct on worker nodes, and the control plane needs a deliberate upgrade process, not a restart.

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Option B is wrong because if the API server were not running, kubectl would return a connection refused or timeout error (e.g., 'Unable to connect to the server'), not an authentication error. Option C is wrong because the error occurs before any pod-specific operation; the client cannot even list pods due to authentication failure, so the existence of a pod is irrelevant. Option D is wrong because the error is about authentication, not authorization to a namespace; a missing namespace would cause a different error like 'namespace not found' or 'the server could not find the requested resource', not an Unauthorized response.

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Option A is wrong because the Service's `port` does not need to match the container's `containerPort`; the `port` is the Service's own listening port, and traffic is forwarded to the `targetPort`. Option B is wrong because a Service of type NodePort still works for internal cluster access (it also gets a ClusterIP), so changing the type to NodePort would not cause a failure to access from within the cluster. Option D is wrong because the question explicitly states that the Service selects pods that are running and responding, meaning the selector matches the pod labels correctly.

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Option A is wrong because kube-proxy is a network proxy that runs on each node to manage network rules (e.g., iptables/IPVS) for Services; its failure would cause connectivity issues to pods/services but does not affect the node's readiness status reported by the kubelet. Option B is wrong because kube-scheduler is a control plane component that runs on the master node(s) and is responsible for assigning pods to nodes; it does not run on worker nodes and has no role in reporting node health. Option D is wrong because while a failing container runtime (e.g., containerd, CRI-O) can prevent pods from starting and may eventually cause the kubelet to mark the node as NotReady, the immediate and direct cause of the 'NotReady' status is the kubelet's failure to report its heartbeat; the kubelet itself is the component that detects runtime failures and updates the node condition accordingly.

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Option A is wrong because a pod in 'Pending' state has not been scheduled to any node; successful scheduling would show a node name in the pod status. Option B is wrong because the taint `node.kubernetes.io/unreachable` is not related to resource insufficiency; resource issues would show taints like `node.kubernetes.io/disk-pressure` or `node.kubernetes.io/memory-pressure`, and the error would mention insufficient resources, not unreachability. Option D is wrong because the error explicitly states '1 node(s) had taint', confirming the node exists but is unreachable; a non-existent node would not appear in the node list or would show a different error like 'node not found'.

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Option B is wrong because a ClusterRole is cluster-scoped and, when used with a RoleBinding, can grant permissions across namespaces if the ClusterRole references cluster-scoped resources; however, for namespace-scoped resources like pods, a Role is more restrictive and appropriate. Option C is wrong because a ClusterRoleBinding grants permissions cluster-wide, which would allow the pipeline to create and delete pods in all namespaces, violating the requirement to restrict access to the 'ci' namespace only. Option D is wrong because a Role cannot be bound with a ClusterRoleBinding; a RoleBinding is required to bind a Role to a subject within a namespace.

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Option A is wrong because `kubectl config set-context` creates or modifies a context entry in the kubeconfig file but does not set it as the current context; it only defines or updates the context's properties (cluster, user, namespace). Option C is wrong because `kubectl config set-cluster` modifies or adds a cluster definition (e.g., server URL, certificate authority) in the kubeconfig, not a context or the current context. Option D is wrong because `kubectl config get-contexts` lists all available contexts or shows details for a specific context, but it does not change the active context.

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Option B is wrong because scheduling pods to nodes is the responsibility of the kube-scheduler, not kube-proxy. Option C is wrong because managing the lifecycle of pods (creation, monitoring, restart) is handled by the kubelet, not kube-proxy. Option D is wrong because storing cluster configuration data is the function of etcd, a distributed key-value store; kube-proxy does not persist any state.

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Option A is wrong because `--grace-period=0` forces immediate termination of pods without a graceful shutdown period, which does not prevent eviction—it actually makes eviction more aggressive. Option B is wrong because `--pod-selector='app=critical'` is not a valid flag for `kubectl drain`; the command does not support a pod-selector to exclude specific pods from eviction. Option D is wrong because `--evict-unscheduled-pods` is not a valid flag for `kubectl drain`; the correct flag is `--evict-unscheduled-pods` (note the typo in the option), and it would evict pods that have not been scheduled to a node, which is irrelevant to protecting a running critical pod.

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Option A is wrong because `spec.serviceAccount` is a deprecated field (removed in Kubernetes 1.24) and should not be used; it was replaced by `spec.serviceAccountName`. Option B is wrong because `spec.authentication.serviceAccount` is not a valid Kubernetes Pod spec field—authentication is handled via the ServiceAccount token, not a nested `authentication` object. Option D is wrong because `spec.accountName` is not a recognized field in the Pod spec; the correct field name is `serviceAccountName`.

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Option A is wrong because 'systemctl status docker' checks the Docker container runtime, not the kubelet; while a runtime failure can cause node issues, the question specifically asks for diagnosing kubelet health. Option B is wrong because 'kubectl get events --all-namespaces' shows cluster-wide events (e.g., pod scheduling failures) but does not provide the kubelet's own log output or system-level errors. Option D is wrong because 'kubectl logs -n kube-system kubelet-<node>' attempts to access a pod named 'kubelet-<node>', but the kubelet does not run as a pod in the kube-system namespace; it runs as a systemd service on the node, so this command would fail with a 'not found' error.

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Option A is wrong because 'Completed' is not a valid Kubernetes pod phase; the correct phase for a successful termination is 'Succeeded'. Option B is wrong because 'Failed' applies only when the container exits with a non-zero exit code, not code 0. Option D is wrong because 'Running' indicates the container is still executing, but here the container has already exited.

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Option A is wrong because `etcdctl dump` is not a valid etcdctl subcommand; it may be confused with `etcdctl get` or `etcdctl watch` but does not exist for snapshotting. Option B is wrong because `etcdctl snapshot create` is not a valid command; the correct subcommand is `snapshot save`, not `create`. Option D is wrong because `etcdctl backup` is not a valid etcdctl command; the `backup` subcommand was used in older etcd v2 but has been replaced by `snapshot save` in etcd v3, which is the version used in modern CKA environments.

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Option A is wrong because kube-controller-manager runs controller loops (e.g., ReplicaSet, Deployment, Node) but does not manage per-node network rules. Option B is wrong because etcd is a distributed key-value store used for cluster state, not for maintaining network rules on nodes. Option D is wrong because kubelet is the primary node agent that manages Pods and containers, but it does not handle network rule enforcement (that is kube-proxy's role).

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Option B is wrong because a Secret is a generic resource for storing sensitive data like passwords or tokens, but it does not automatically provide authentication credentials to a pod; you must explicitly mount or reference it, and it lacks the automatic token rotation and API server integration of a ServiceAccount. Option C is wrong because a ConfigMap is designed for non-sensitive configuration data (e.g., environment variables or config files) and cannot store or provide authentication credentials. Option D is wrong because a ClusterRoleBinding grants RBAC permissions to a subject (like a ServiceAccount or user) but does not itself provide authentication credentials; it is an authorization resource, not an authentication mechanism.

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Option A is wrong because cordoning does not remove the node from the cluster; the node remains a member and can be uncordoned later. Option B is wrong because `kubectl drain` is not automatically performed; draining is a separate, explicit operation that evicts pods, whereas cordon only prevents new scheduling. Option D is wrong because existing pods are not immediately evicted; they continue running until they are terminated or the node is drained manually.

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Option A is wrong because the container runtime (e.g., containerd, CRI-O) runs containers, not the kube-scheduler. Option B is wrong because managing network rules for services is the job of the kube-proxy component, which implements Service networking via iptables/IPVS. Option C is wrong because storing cluster state is the responsibility of etcd, a distributed key-value store; the kube-scheduler does not persist any state.

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Option A is wrong because upgrading worker nodes before control plane nodes violates the Kubernetes upgrade order; the control plane must be upgraded first to avoid version skew incompatibilities. Option B is wrong because upgrading worker nodes without draining them first can cause pod disruptions and data loss, as the kubelet is stopped during the upgrade and pods are not gracefully terminated. Option D is wrong because upgrading all nodes simultaneously is not supported; Kubernetes requires a sequential upgrade to maintain cluster stability and prevent version mismatch between components.