Kubernetes

Kubernetes - kubectl + Manifest Authoring

Overview

Kubernetes runs containerized workloads against a declarative API. You don't tell it how to run things; you declare what you want (a manifest's spec) and the system continuously works to make reality (status) match. kubectl is the CLI you use to submit that desired state and to inspect, debug, and roll out workloads against any cluster — regardless of how the cluster was built.

This skill is the kubectl + resource/manifest layer: authoring core API objects and driving the API with kubectl. It is independent of how the cluster was stood up.

Disambiguation: This skill documents kubectl and core-resource manifest authoring — how to write Kubernetes objects and drive the API. It does not cover installing or administering a cluster. To run a local or lightweight cluster (install a single binary, join nodes, etcd snapshots, bundled ingress/LB/DNS, certs), use the k3s skill. Out of scope entirely: client libraries (client-go), cloud-provider specifics (EKS/GKE/AKS IAM, cloud LBs/CSI), and Helm (mention as a packaging option, defer).

Mental Model

Four ideas unlock everything:

1. Declarative desired state. You declare what you want in a manifest (spec); the system drives reality (status) to match. kubectl apply submits desired state; controllers do the rest.
2. Control loops (reconciliation). Every resource type has a controller that watches and drives status toward spec. A Deployment controller creates a ReplicaSet; the ReplicaSet controller creates Pods; the scheduler binds Pods to Nodes; the kubelet runs containers. Self-healing falls out of this for free.
3. Everything is an API object addressed by Group / Version / Kind (GVK): apiVersion: apps/v1 + kind: Deployment. The empty "core" group is written as just v1 (Pod, Service, ConfigMap, Secret, Namespace). Named groups include apps/v1, batch/v1, networking.k8s.io/v1, rbac.authorization.k8s.io/v1, policy/v1, autoscaling/v2, storage.k8s.io/v1. Run kubectl api-resources to see the live map.
4. Namespaces scope most resources (Pods, Deployments, Services, ConfigMaps…). Cluster-scoped resources (Nodes, PersistentVolumes, Namespaces, ClusterRoles, StorageClasses, PriorityClasses) live outside any namespace. default exists out of the box; kube-system holds control-plane add-ons.

Every object shares a shape: apiVersion, kind, metadata (name, namespace, labels, annotations), spec (desired), status (observed, managed by the system — never author it).

When to Use This Skill

Use this skill when:

• Writing/editing manifests (YAML) for any core resource.
• Driving kubectl: deploy, inspect, debug, roll out, scale, exec/logs, port-forward, generate manifests, check RBAC.
• Debugging a workload: a Pod stuck Pending, CrashLoopBackOff, ImagePullBackOff, OOMKilled; reading events; describing resources.
• Managing contexts/namespaces across clusters via kubeconfig.

Relationship to the k3s skill

This skill is the kubectl + resource/manifest layer — authoring Kubernetes objects and driving the API with kubectl, regardless of how the cluster was created. It does not cover standing up or administering a cluster. To run a local or lightweight cluster (install the single k3s binary, join nodes, snapshots, bundled ingress/LB/DNS/storage, certs), use the k3s skill. k3s hands you a working API endpoint and a kubeconfig; this skill is everything you do against it. (k3s even bundles kubectl — every command here works on a k3s cluster.) Out of scope: client libraries, cloud-provider specifics, and Helm.

Prerequisites

CRITICAL: Before proceeding, verify kubectl is installed and check the version:

kubectl version --client     # prints e.g. "Client Version: v1.28.2"

Version note: This skill is documented against the Kubernetes API as of ~1.37; the empirical CLI baseline is kubectl v1.28.2 (bundled kustomize v5.0.4). Long-standing features (GA at or before 1.20) are "bedrock" and shown unannotated. Features added later are tagged inline as (k8s 1.X+) by their GA version — see references/version-features.md for the full feature → version map with source citations. Version skew: keep kubectl within ±1 minor of the cluster.

Install kubectl + kubeconfig/contexts

# macOS
brew install kubectl
# Linux (direct binary, matching minor)
curl -LO "https://dl.k8s.io/release/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl"
sudo install -o root -g root -m 0755 kubectl /usr/local/bin/kubectl
kubectl version --client     # verify

(For a cluster to point it at, see the k3s skill.)

kubeconfig lives at ~/.kube/config (override with $KUBECONFIG, which may be a :-separated list that gets merged). It holds three lists — clusters (API server URL + CA), users (credentials), contexts (a cluster+user+namespace triple) — plus a current-context.

kubectl config get-contexts                              # list; * marks current
kubectl config use-context <ctx>                         # switch cluster
kubectl config set-context --current --namespace=<ns>    # set default namespace
kubectl config view --minify                             # effective config for current ctx

(kubectx / kubens are popular third-party helpers for switching contexts/namespaces.)

Core Workflows

1. Deploy + expose

kubectl create deployment web --image=nginx --replicas=3      # imperative, quick
kubectl expose deployment web --port=80 --target-port=8080    # creates a ClusterIP Service
kubectl get deploy,rs,pods,svc -l app=web

Prefer declarative for anything you keep: generate with --dry-run=client -o yaml > web.yaml, edit, then kubectl apply -f web.yaml.

2. Inspect / debug a failing pod

kubectl get pods                      # the STATUS column tells the story
kubectl describe pod <pod>            # Events at the bottom are the #1 clue
kubectl logs <pod> [-c <container>] [--previous]   # --previous = last crashed container
kubectl get events --sort-by=.lastTimestamp        # or: kubectl events

Map STATUS → cause in Troubleshooting below.

3. Apply / diff / rollout cycle

kubectl diff -f web.yaml              # preview what apply would change
kubectl apply -f web.yaml             # converge to desired state
kubectl rollout status deploy/web     # wait for the rollout to finish
kubectl rollout history deploy/web
kubectl rollout undo deploy/web       # roll back to previous revision
kubectl rollout restart deploy/web    # re-roll pods (e.g. to pick up a changed Secret)

4. Exec / logs / port-forward

kubectl exec -it <pod> -- sh                       # shell in a running container
kubectl logs -f deploy/web                         # stream logs (Deployment → a pod)
kubectl port-forward svc/web 8080:80               # localhost:8080 → Service:80

5. Generate manifests with --dry-run=client (offline, no cluster)

kubectl create deployment web --image=nginx --dry-run=client -o yaml
kubectl create configmap app-cfg --from-literal=LOG=info --dry-run=client -o yaml
kubectl create cronjob nightly --image=busybox --schedule="0 2 * * *" --dry-run=client -o yaml

These emit clean starter YAML you then edit (verified emitting on 1.28.2: deployment→apps/v1, job/cronjob→batch/v1, service/cm/secret→v1, rolebinding→rbac.authorization.k8s.io/v1, ingress→networking.k8s.io/v1, pdb→policy/v1, priorityclass→scheduling.k8s.io/v1).

Not offline generators. kubectl run, kubectl expose, kubectl autoscale, and kubectl create role --resource=… consult the API server even under --dry-run=client (for resource/GVR resolution), so they need a reachable cluster. Don't expect them to render YAML with no cluster.

6. RBAC quick-check with auth can-i

kubectl auth can-i create deployments                          # for yourself
kubectl auth can-i get pods --as=system:serviceaccount:ns:sa   # impersonate
kubectl auth can-i --list                                      # everything you can do
kubectl auth whoami                                            # who am I (Experimental in 1.28)

Quick Reference

Troubleshooting

A failing Pod's STATUS column is the fastest diagnostic. Map it to a cause, then confirm with kubectl describe pod <pod> (read the Events at the bottom).

Common kubectl errors:

• The connection to the server <host> was refused → wrong/empty context or cluster down. Check kubectl config current-context and your kubeconfig.
• error: You must be logged in to the server (Unauthorized) → bad/expired credentials.
• Error from server (Forbidden) → RBAC; confirm what you can do with kubectl auth can-i.
• Error from server (NotFound) → wrong namespace (try -n <ns> / -A) or the object is truly absent.
• no matches for kind "X" in version "Y" → a CRD isn't installed, or the wrong apiVersion.

References

For exhaustive detail, see the bundled reference files:

• references/kubectl.md — the full kubectl CLI: verbs, output formats (-o jsonpath/custom-columns/go-template), selectors, the apply model (client- vs server-side, --prune), diff, rollout, scale/autoscale, exec/logs/cp/port-forward/proxy, debug, node ops (drain/cordon/taint), auth can-i, api-resources/explain, config, kustomize (-k), events, top, --dry-run, wait, --subresource, and plugins/krew.
• references/workloads.md — manifest authoring for workloads: Pod spec essentials (env, resources, probes, securityContext, init/sidecar containers, volumes), Deployment, ReplicaSet, StatefulSet, DaemonSet, Job, CronJob, HorizontalPodAutoscaler, PodDisruptionBudget, and scheduling controls (affinity, topology spread, tolerations, priority).
• references/cluster-resources.md — Service (incl. headless), Ingress/IngressClass, NetworkPolicy, ConfigMap/Secret, storage (PV/PVC/StorageClass, access modes), Namespace/ResourceQuota/LimitRange, RBAC (Role/ClusterRole/bindings/aggregation), ServiceAccount + bound tokens, DNS conventions, and the Downward API.
• references/version-features.md — source-cited feature → minimum-version map (what's bedrock vs. added later), so you know when each (k8s 1.X+) annotation applies.

Resources

• Help: kubectl help, kubectl <verb> --help, kubectl explain <type>[.<path>]
• Official docs: https://kubernetes.io/docs/
• Reference: https://kubernetes.io/docs/reference/kubectl/
• API reference: https://kubernetes.io/docs/reference/kubernetes-api/