vumast3r e07ee1beab refactor: CKA_SOLUTIONS_EXPLAINED.md + 12 files

2026-10-05 16:30:46 -06:00

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CKA study guide

The 27 objectives of the Certified Kubernetes Administrator curriculum, in its own words and order: what to know, the fastest commands, the traps, the documentation pages the exam lets you open, and the tasks in this simulator that practise each one.

Generated by ./exam --track cka notes all --md from tracks/cka/curriculum.py - edit that file, not this one.

./exam objectives        # the path and your progress
./exam study 3.2         # one objective: these notes, then its tasks, no clock, solutions open
./exam drill 3.2         # the same tasks against the clock

Storage (10%)

1.1 Implement storage classes and dynamic volume provisioning

./exam study 1.1 (or storageclasses)

Know

A StorageClass names a provisioner and its settings. A claim that asks for the class gets a PersistentVolume made for it - that is dynamic provisioning.
Fields: provisioner, reclaimPolicy (Delete by default, or Retain), volumeBindingMode (Immediate or WaitForFirstConsumer), allowVolumeExpansion, parameters.
The default class carries the annotation storageclass.kubernetes.io/is-default-class: "true"; a claim with no storageClassName gets it. storageClassName: "" asks for no class at all.
A StatefulSet's volumeClaimTemplates make one claim per replica (data-web-0, data-web-1 ...).

Fast

k get sc                                              # (default) marks the default class
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata: {name: fast-local}
provisioner: rancher.io/local-path
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
---
k patch sc standard   -p '{"metadata":{"annotations":{"storageclass.kubernetes.io/is-default-class":"false"}}}'
k patch sc fast-local -p '{"metadata":{"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'
k get pvc,pv;  k describe pvc data                    # the Events say why a claim is Pending

Traps

With WaitForFirstConsumer a claim stays Pending until a Pod uses it. That is not an error.
Leave exactly one class marked default: take the annotation off the old one as well as putting it on the new one.
provisioner, reclaimPolicy and volumeBindingMode cannot be edited - delete the class and create it again.

Docs

Tasks

Q16 Default StorageClass and dynamic provisioning
Q36 Data survives the pod
Q59 Migrate data between claims
Q99 Per-replica storage for a StatefulSet (Simulator Set D (killer.sh-style))

1.2 Configure volume types, access modes and reclaim policies

./exam study 1.2 (or volumes)

Know

Volume types you meet: hostPath (a directory of whatever node the Pod lands on), local (a disk of one node, needs nodeAffinity), emptyDir, nfs, csi, and the configMap / secret / projected volumes.
Access modes: ReadWriteOnce (one node), ReadOnlyMany, ReadWriteMany, ReadWriteOncePod (one Pod). A claim binds only to a volume that offers its mode.
The reclaim policy is on the PersistentVolume: Retain keeps the volume and its data when the claim goes (it becomes Released), Delete removes both.

Fast

apiVersion: v1
kind: PersistentVolume
metadata: {name: pv-data}
spec:
  capacity: {storage: 1Gi}
  accessModes: [ReadWriteOnce]
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath: {path: /mnt/data}
---
k patch pv pv-data -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'
k patch pv pv-data --type=json -p '[{"op":"remove","path":"/spec/claimRef"}]'      # Released -> Available
k get pv -o custom-columns=NAME:.metadata.name,MODES:.spec.accessModes,RECLAIM:.spec.persistentVolumeReclaimPolicy,STATUS:.status.phase,CLAIM:.spec.claimRef.name

Traps

A Released volume never binds again by itself: remove its claimRef first.
A local volume needs spec.nodeAffinity; a hostPath volume does not pin the Pod to the node that has the data.
The local-path provisioner of this cluster only does ReadWriteOnce and ReadWriteOncePod - a ReadWriteMany claim stays Pending.

Docs

Tasks

Q15 PersistentVolume, claim and pod
Q35 Re-bind a Released PersistentVolume
Q58 Bind the right local volume
Q68 Provision geo-fence persistent storage (Simulator Set C)
Q72 Migrate ride history to a Retain volume (Simulator Set C)
Q102 A claim that can never bind (Simulator Set D (killer.sh-style))

1.3 Manage persistent volumes and persistent volume claims

./exam study 1.3 (or claims)

Know

A claim binds to one volume, and only if class, access mode and size fit (the volume may be larger); volumeName or a selector narrows it to one volume.
Phases: a volume goes Available, Bound, Released; a claim Pending, Bound.
A Pod mounts a claim of its own Namespace: volumes[].persistentVolumeClaim.claimName, then volumeMounts.
A claim in use is protected: deleting it waits (Terminating) until no Pod references it, finished Pods included.

Fast

apiVersion: v1
kind: PersistentVolumeClaim
metadata: {name: pvc-data, namespace: storage}
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: manual               # omit for the default class
  resources: {requests: {storage: 500Mi}}
---                                       # in the Pod:
volumes: [{name: data, persistentVolumeClaim: {claimName: pvc-data}}]
containers: [{..., volumeMounts: [{name: data, mountPath: /data}]}]
k get pvc,pv -A;  k describe pvc pvc-data       # Used By: and Events:
k describe pod POD | tail                       # unbound claim -> the Pod stays Pending

Traps

There is no kubectl create pvc or create pv - copy both from the docs.
For a hand-made volume the claim's storageClassName has to equal the volume's exactly; leaving it out means the default class, not none.
Apart from growing the request (and only if the class allows expansion) a claim cannot be edited.
To move data between claims, run a Pod or Job that mounts both.

Docs

Tasks

Q15 PersistentVolume, claim and pod
Q36 Data survives the pod
Q35 Re-bind a Released PersistentVolume
Q58 Bind the right local volume
Q59 Migrate data between claims
Q68 Provision geo-fence persistent storage (Simulator Set C)
Q72 Migrate ride history to a Retain volume (Simulator Set C)
Q81 Fix the fare calculation pods (Simulator Set C)
Q99 Per-replica storage for a StatefulSet (Simulator Set D (killer.sh-style))
Q102 A claim that can never bind (Simulator Set D (killer.sh-style))

Troubleshooting (30%)

2.1 Troubleshoot clusters and nodes

./exam study 2.1 (or nodes)

Know

Start from the cluster: k get nodes, then k describe node - Conditions, Taints, Unschedulable, Events.
A NotReady node is nearly always its kubelet: on the node, systemctl status kubelet and journalctl -u kubelet name the cause.
What the kubelet needs: its unit and drop-in (which binary, which flags), /var/lib/kubelet/config.yaml, /etc/kubernetes/kubelet.conf (its kubeconfig), its certificates in /var/lib/kubelet/pki, and a running container runtime.
Ready but SchedulingDisabled is a cordon, not a fault: k uncordon.

Fast

k get nodes -o wide;  k describe node NODE | sed -n '/Conditions/,/Addresses/p'
ssh NODE
systemctl status kubelet;  journalctl -u kubelet --no-pager | tail -30
systemctl cat kubelet                         # the unit and its drop-ins: ExecStart, EnvironmentFile
cat /var/lib/kubelet/config.yaml;  cat /var/lib/kubelet/kubeadm-flags.env
systemctl daemon-reload;  systemctl enable --now kubelet;  systemctl restart kubelet
systemctl status containerd;  crictl ps -a
k uncordon NODE;  k describe node NODE | grep -i taint

Traps

A kubelet that was stopped is often disabled too: enable --now, or it is gone again after a reboot.
After changing a unit file nothing happens until systemctl daemon-reload.
There may be more than one fault. After every fix read the journal again instead of assuming you are done.

Docs

Tasks

Q17 Node NotReady
Q39 kubelet misconfiguration
Q60 Worker node: three things wrong
Q92 Kubelet unit points at nothing (Simulator Set D (killer.sh-style))
Q90 Event forensics around kube-proxy (Simulator Set D (killer.sh-style))
Q95 The kubelet's two certificates (Simulator Set D (killer.sh-style))

2.2 Troubleshoot cluster components

./exam study 2.2 (or components)

Know

kube-apiserver, kube-scheduler, kube-controller-manager and etcd run as static Pods: the kubelet starts whatever is in /etc/kubernetes/manifests and restarts it when the file changes.
Read the symptom: Pods stay Pending with no events - scheduler. Deployments make no ReplicaSet or Pods - controller-manager. kubectl is refused - API server (or etcd behind it).
With the API server up: k -n kube-system get pods, logs, describe. With it down: crictl ps -a, crictl logs, /var/log/pods and the kubelet's journal on the node.

Fast

k -n kube-system get pods;  k -n kube-system logs kube-scheduler-NODE;  k -n kube-system describe pod kube-scheduler-NODE
ssh CONTROL-PLANE
ls /etc/kubernetes/manifests;  vi /etc/kubernetes/manifests/kube-scheduler.yaml
crictl ps -a | grep -E 'kube-|etcd';  crictl logs CONTAINER-ID
ls /var/log/pods/kube-system_kube-apiserver-*/kube-apiserver/        # its logs when kubectl cannot ask for them
journalctl -u kubelet --no-pager | grep -i -E 'manifest|apiserver' | tail

Traps

The faults are small: a misspelt image, binary or flag, a wrong path in a volume or certificate flag, a wrong port in a probe.
Do not leave a backup copy inside the manifests directory - the kubelet runs every file there.
After saving a manifest give the kubelet up to a minute before deciding the fix did not work.

Docs

Tasks

Q20 Control plane component failure
Q38 Deployments never create pods
Q61 Two control-plane components down
Q66 Nothing works: kube-apiserver itself is down
Q97 Stop the scheduler, schedule by hand (Simulator Set D (killer.sh-style))
Q86 How the control plane is run (Simulator Set D (killer.sh-style))

2.3 Monitor cluster and application resource usage

./exam study 2.3 (or usage)

Know

kubectl top node|pod shows live CPU and memory from metrics-server through the metrics API (metrics.k8s.io); --containers splits a Pod up, --sort-by=cpu|memory orders it.
k describe node shows what is allocated - the sum of requests and limits - which is not what is used.
kubectl get sorts and shapes everything else: --sort-by, -o custom-columns, -o jsonpath, -A.

Fast

k top node;  k top pod -A --sort-by=memory | head;  k top pod -n NS --containers
k describe node NODE | grep -A8 'Allocated resources'
k get pods -A --sort-by='.status.containerStatuses[0].restartCount'
k -n kube-system get deploy metrics-server;  k get apiservice v1beta1.metrics.k8s.io
k -n kube-system logs deploy/metrics-server

Traps

Metrics API not available means metrics-server is missing or not Ready (on this cluster it needs --kubelet-insecure-tls).
kubectl top --sort-by puts the largest first; kubectl get --sort-by puts it last.
A new Pod has no metrics for about a minute.

Docs

Tasks

Q103 Find the heaviest Pods with kubectl top
Q23 metrics-server repair and HPA
Q53 Namespace audit to exact files
Q85 Investigate vehicle tracker health (Simulator Set C)
Q89 Sorting done by kubectl (Simulator Set D (killer.sh-style))

2.4 Manage and evaluate container output streams

./exam study 2.4 (or logs)

Know

kubectl logs shows what a container wrote to stdout and stderr. The runtime keeps it on the node under /var/log/pods/NAMESPACE_POD_UID/CONTAINER/, and it goes when the Pod is deleted.
Pick the container with -c (init containers too) or take --all-containers; --previous is the run before the last restart.
Narrow with --tail=N, --since=10m, --timestamps; follow with -f; take every Pod of a label with -l and tell them apart with --prefix.
On a node, without the API server: crictl logs CONTAINER-ID.

Fast

k logs POD -c CONTAINER                       # --all-containers --prefix
k logs POD --previous                         # the crashed run
k logs POD --tail=50 --since=10m --timestamps
k logs -l app=web --prefix --tail=5           # every Pod with the label
k logs deploy/web;  k logs job/render         # one Pod of it
k logs POD | grep ERROR > errors.log
crictl ps -a;  crictl logs --tail=20 CONTAINER-ID;  ls /var/log/pods/

Traps

With -l, only the last 10 lines of each Pod are shown unless you set --tail (--tail=-1 for everything).
kubectl logs deploy/x reads one Pod, not all replicas.
--previous fails when the container has never restarted.

Docs

Tasks

Q19 CrashLoopBackOff diagnosis
Q104 One replica is logging errors
Q8 Multi-container pod with shared volume
Q85 Investigate vehicle tracker health (Simulator Set C)

2.5 Troubleshoot services and networking

./exam study 2.5 (or netdebug)

Know

Work outwards from the Pod: is it Ready, does the Service have endpoints (selector against Pod labels), is targetPort the port the container listens on, does the name resolve, does a NetworkPolicy stand in the way.
DNS is a Service like any other: the CoreDNS Pods, the kube-dns Service and its endpoints, the Corefile in ConfigMap coredns.
Underneath: kube-proxy (a DaemonSet) turns Services into rules on every node, and the CNI plugin connects the Pods.

Fast

k get svc,endpointslices -o wide;  k describe svc SVC          # Endpoints: <none> = nothing selected
k get pods -l KEY=VALUE --show-labels -o wide
k run tmp --rm -it --restart=Never --image=busybox:1.36 -- sh  # wget -qO- -T3 http://SVC:PORT ; nslookup SVC.NS.svc.cluster.local
k -n kube-system get pods -l k8s-app=kube-dns -o wide;  k -n kube-system logs -l k8s-app=kube-dns
k -n kube-system get cm coredns -o yaml;  k -n kube-system get svc,endpointslices -l k8s-app=kube-dns
k -n kube-system get ds kube-proxy;  k -n kube-system logs ds/kube-proxy
k get netpol -A

Traps

A Service with no endpoints still resolves - it is the connection that fails.
Test names with the fully qualified form (SVC.NS.svc.cluster.local): busybox's nslookup misreports short ones.
A NetworkPolicy in kube-system can cut DNS off for the whole cluster.
Fix what is broken and leave the rest alone - the graders check what you did not have to touch.

Docs

Tasks

Q18 Broken deployment and service
Q62 Application down for four reasons
Q37 Cluster DNS is broken
Q57 DNS down: three faults
Q73 Fix ETA service connectivity (Simulator Set C)
Q101 Resolves everything except the cluster (Simulator Set D (killer.sh-style))
Q70 Fix the driver onboarding app (Simulator Set C)
Q90 Event forensics around kube-proxy (Simulator Set D (killer.sh-style))

Workloads & Scheduling (15%)

3.1 Understand application deployments and how to perform rolling update and rollbacks

./exam study 3.1 (or rollouts)

Know

Any change to spec.template starts a rollout: a new ReplicaSet scales up while the old one scales down, within maxSurge and maxUnavailable (25% each by default).
Every rollout is a revision. kubectl rollout: status, history, undo, pause, resume, restart.
minReadySeconds, revisionHistoryLimit and progressDeadlineSeconds tune how careful and how patient a rollout is.

Fast

k set image deploy/web nginx=nginx:1.27                  # CONTAINER=IMAGE
k scale deploy/web --replicas=4
k rollout status deploy/web
k rollout history deploy/web;  k rollout history deploy/web --revision=2      # that revision's template
k rollout undo deploy/web --to-revision=2
k rollout pause deploy/web;  k rollout resume deploy/web
k patch deploy web -p '{"spec":{"strategy":{"rollingUpdate":{"maxSurge":1,"maxUnavailable":0}}}}'

Traps

To go back to a particular image, look at each revision's template first - "the previous one" is not always the one asked for.
An undo makes a new revision out of the old one, so the numbers keep climbing.
A paused Deployment records changes but rolls nothing out until it is resumed.
maxSurge and maxUnavailable cannot both be 0.

Docs

https://kubernetes.io/docs/concepts/workloads/controllers/deployment/

Tasks

Q7 Rolling update & scaling
Q51 Rollback to a specific revision, then pause

3.2 Use ConfigMaps and Secrets to configure applications

./exam study 3.2 (or config)

Know

Both hold keys. A key becomes an environment variable (configMapKeyRef / secretKeyRef, or every key at once with envFrom) or a file (a configMap / secret volume; items picks and renames keys).
Secret data is base64 - an encoding, not encryption. Types: Opaque, kubernetes.io/tls, kubernetes.io/dockerconfigjson.
Mounted files follow a change after a short delay. Environment variables and subPath mounts never do: restart the Pods.
immutable: true freezes one for good. To change the content, make a new object and point the workload at it.

Fast

k create cm app-config --from-literal=APP_MODE=production --from-file=app.properties
k create secret generic db-creds --from-literal=username=admin --from-literal=password='S3cr3t!'
k create secret tls web-tls --cert=tls.crt --key=tls.key
k get secret db-creds -o jsonpath='{.data.password}' | base64 -d
env:
  - {name: APP_MODE, valueFrom: {configMapKeyRef: {name: app-config, key: APP_MODE}}}
  - {name: DB_PASS,  valueFrom: {secretKeyRef: {name: db-creds, key: password}}}
envFrom: [{configMapRef: {name: app-config}}, {secretRef: {name: db-creds}}]
volumes: [{name: creds, secret: {secretName: db-creds, defaultMode: 0400}}]
k set env deploy/web --from=configmap/app-config;  k rollout restart deploy/web

Traps

A secret volume names it with secretName; a configMap volume uses name.
A Pod that references a missing ConfigMap, Secret or key waits in CreateContainerConfigError.
--from-file makes one key named after the file; --from-env-file makes one key per line.

Docs

Tasks

Q10 ConfigMap and Secret consumption
Q29 Immutable ConfigMap rotation
Q79 Surge pricing configuration (Simulator Set C)
Q93 Secrets as a read-only volume and renamed env vars (Simulator Set D (killer.sh-style))
Q84 Enforce TLS 1.3 on the booking portal (Simulator Set C)

3.3 Configure workload autoscaling

./exam study 3.3 (or autoscaling)

Know

A HorizontalPodAutoscaler (autoscaling/v2) keeps a workload between minReplicas and maxReplicas by a metric - usually average CPU or memory utilisation, which is usage divided by the container's request.
It reads the metrics API, so it needs metrics-server, and the containers need a request for the resource it scales on.
behavior shapes the change: scaleUp and scaleDown each take a stabilizationWindowSeconds and policies (so many Pods or Percent per periodSeconds).

Fast

k set resources deploy web --requests=cpu=100m
k autoscale deploy web --min=2 --max=6 --cpu=60%            # kubectl before 1.34: --cpu-percent=60
k get hpa;  k describe hpa web
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata: {name: web}
spec:
  scaleTargetRef: {apiVersion: apps/v1, kind: Deployment, name: web}
  minReplicas: 2
  maxReplicas: 6
  metrics:
    - type: Resource
      resource: {name: cpu, target: {type: Utilization, averageUtilization: 60}}
  behavior:
    scaleDown:
      stabilizationWindowSeconds: 300
      policies: [{type: Pods, value: 1, periodSeconds: 60}]

Traps

TARGETS <unknown>: no metrics-server, or no request on the containers.
kubectl autoscale cannot write behavior - edit the object or write the YAML.
minReplicas is enforced at once, even without metrics.

Docs

Tasks

Q105 Autoscale on CPU, scale down calmly
Q23 metrics-server repair and HPA
Q82 Autoscale the route planner on memory (Simulator Set C)

3.4 Understand the primitives used to create robust, self-healing, application deployments

./exam study 3.4 (or selfhealing)

Know

Controllers put back what is missing: a Deployment its replicas, a DaemonSet one Pod per node, a StatefulSet named replicas with their own storage, a Job its completions (backoffLimit retries), a CronJob its Jobs.
Probes tell the kubelet about health: liveness restarts the container, readiness takes the Pod out of Service endpoints, startup holds both off until the app is up.
Init containers run to completion, in order, before the app starts; a native sidecar (an init container with restartPolicy: Always) keeps running beside it.
A PodDisruptionBudget (minAvailable or maxUnavailable) limits how many Pods a drain may take away at once.

Fast

containers:
  - name: app
    startupProbe:   {httpGet: {path: /, port: 80}, periodSeconds: 5, failureThreshold: 12}
    readinessProbe: {httpGet: {path: /ready, port: 8080}, periodSeconds: 5}
    livenessProbe:  {tcpSocket: {port: 80}, initialDelaySeconds: 15, periodSeconds: 10}
    # exec: {exec: {command: [cat, /tmp/ready]}}
k create job render --image=busybox:1.36 -- sh -c 'echo done'
k create cronjob digest --image=busybox:1.36 --schedule='*/5 * * * *' -- date;  k create job run-1 --from=cronjob/digest
k create pdb web --selector=app=web --min-available=2
k create deploy x --image=busybox:1.36 $do > ds.yaml        # DaemonSet: change kind, drop replicas / strategy / status
k describe pod POD | grep -E 'Liveness|Readiness|Startup';  k get events --field-selector reason=Unhealthy

Traps

Probes belong to a container. No kubectl flag adds one - edit the YAML.
Restarts with Unhealthy and Killing events but a clean log: the liveness probe is wrong, not the app.
A DaemonSet reaches control-plane nodes only with a toleration for node-role.kubernetes.io/control-plane.
A Job's Pod template cannot be edited: delete the Job and create it again.

Docs

Tasks

Q106 Health checks that check the wrong thing
Q8 Multi-container pod with shared volume
Q28 Init container prepares content
Q26 DaemonSet on every node
Q27 CronJob with a manual run
Q31 Parallel Job
Q52 Native sidecar with probes and an exact report
Q53 Namespace audit to exact files
Q76 Add an init container to the trip logger (Simulator Set C)
Q88 Ready only when its dependency answers (Simulator Set D (killer.sh-style))
Q70 Fix the driver onboarding app (Simulator Set C)

3.5 Configure Pod admission and scheduling (limits, node affinity, etc.)

./exam study 3.5 (or scheduling)

Know

Requests are what the scheduler reserves, limits what the node enforces. A LimitRange gives containers defaults and bounds; a ResourceQuota caps a Namespace's totals - both act at admission.
Where a Pod may go: nodeSelector, node affinity (required or preferred), Pod affinity and anti-affinity with a topologyKey, topologySpreadConstraints, or nodeName, which skips the scheduler.
Taints keep Pods off a node (NoSchedule, PreferNoSchedule, NoExecute); a toleration lets a Pod through.
A PriorityClass orders Pods when room is short; the Pod names it in priorityClassName.

Fast

k label node NODE disktype=ssd
k taint node NODE dedicated=gpu:NoSchedule;  k taint node NODE dedicated-          # the trailing - removes it
tolerations: [{key: dedicated, operator: Equal, value: gpu, effect: NoSchedule}]
affinity:
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms: [{matchExpressions: [{key: disktype, operator: In, values: [ssd]}]}]
  podAntiAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      - {labelSelector: {matchLabels: {app: web}}, topologyKey: kubernetes.io/hostname}
k create priorityclass high --value=100000 --description='critical workloads'
k create quota team -n NS --hard=pods=5,requests.cpu=1,limits.memory=2Gi
k describe pod POD | tail                    # FailedScheduling: 0/4 nodes are available: ...

Traps

A toleration lets a Pod onto a tainted node but does not send it there - pair it with a nodeSelector or affinity.
Once a quota covers CPU or memory, every new Pod must state them or get them from a LimitRange.
In a LimitRange, default is the limit and defaultRequest the request.
Scheduling fields of a running Pod cannot be changed: change the Deployment, or delete and recreate the Pod.

Docs

Tasks

Q9 Scheduling with node affinity and resources
Q25 Taints and tolerations
Q24 PriorityClass
Q32 ResourceQuota and LimitRange
Q50 Spread, tolerate, prioritise — under a quota
Q78 Priority for the rider support portal (Simulator Set C)
Q96 A Pod for the control plane only (Simulator Set D (killer.sh-style))
Q81 Fix the fare calculation pods (Simulator Set C)
Q97 Stop the scheduler, schedule by hand (Simulator Set D (killer.sh-style))

Cluster Architecture, Installation & Configuration (25%)

4.1 Manage role based access control (RBAC)

./exam study 4.1 (or rbac)

Know

A Role (one Namespace) or ClusterRole (everywhere, and cluster-scoped resources) lists verbs on resources; a RoleBinding or ClusterRoleBinding grants it to users, groups or ServiceAccounts.
A RoleBinding may point at a ClusterRole: the rules then apply in that one Namespace only.
A user is a certificate: CN is the name, O the groups. Create a key and CSR, submit a CertificateSigningRequest, approve it, put the certificate in a kubeconfig.
An aggregated ClusterRole has no rules of its own: the controller fills them in from every ClusterRole carrying the label it selects.

Fast

k create role deploy-manager -n NS --verb=get,list,watch,create,update,patch,delete --resource=deployments.apps
k create rolebinding deploy-bot -n NS --role=deploy-manager --serviceaccount=NS:deploy-bot     # --user=jane  --group=devs
k create clusterrole node-reader --verb=get,list,watch --resource=nodes
k create clusterrolebinding node-reader --clusterrole=node-reader --serviceaccount=NS:SA
k auth can-i create deployments -n NS --as=system:serviceaccount:NS:deploy-bot;  k auth can-i --list --as=jane -n NS
openssl genrsa -out jane.key 2048;  openssl req -new -key jane.key -subj '/CN=jane/O=developers' -out jane.csr
# CertificateSigningRequest: spec.request = base64 -w0 of the .csr, signerName kubernetes.io/kube-apiserver-client, usages [client auth]
k certificate approve jane;  k get csr jane -o jsonpath='{.status.certificate}' | base64 -d > jane.crt
k config set-credentials jane --client-certificate=jane.crt --client-key=jane.key --embed-certs

Traps

"Exactly these permissions" also means finding what is already granted: k get rolebindings,clusterrolebindings -A -o wide | grep NAME.
Deployments are in the group apps: --resource=deployments.apps; a subresource is deployments.apps/scale, pods/log.
The same ServiceAccount is --serviceaccount=NS:NAME in a binding and system:serviceaccount:NS:NAME after --as.
Nodes, PersistentVolumes and Namespaces are cluster-scoped: they need a ClusterRole and a ClusterRoleBinding.

Docs

Tasks

Q1 RBAC for a deployment bot
Q33 Aggregated ClusterRole
Q6 Certificates: expiry check and user CSR
Q44 Exact RBAC with an existing over-grant
Q47 User onboarding to a working kubeconfig
Q75 Cluster-wide read access for the auth team (Simulator Set C)
Q91 API resources and a Role census (Simulator Set D (killer.sh-style))

4.2 Prepare underlying infrastructure for installing a Kubernetes cluster

./exam study 4.2 (or infra)

Know

Every machine needs, before kubeadm: a container runtime (containerd) using the same cgroup driver as the kubelet (systemd), the kernel modules overlay and br_netfilter, the sysctls net.bridge.bridge-nf-call-iptables and net.ipv4.ip_forward, and swap off or accounted for.
kubeadm, kubelet and kubectl come from the package repository of one minor version (pkgs.k8s.io) and are held, so that a system update does not move them.
Also: a unique hostname, MAC address and product_uuid per node, and the ports open - 6443 (API), 10250 (kubelet), 2379-2380 (etcd).

Fast

printf 'overlay\nbr_netfilter\n' > /etc/modules-load.d/k8s.conf;  modprobe overlay;  modprobe br_netfilter
cat > /etc/sysctl.d/k8s.conf <<EOF
net.bridge.bridge-nf-call-iptables  = 1
net.bridge.bridge-nf-call-ip6tables = 1
net.ipv4.ip_forward                 = 1
EOF
sysctl --system
swapoff -a;  sed -i '/ swap / s/^/#/' /etc/fstab;  cat /proc/swaps
systemctl enable --now containerd;  grep SystemdCgroup /etc/containerd/config.toml
apt-get install -y kubelet kubeadm kubectl;  apt-mark hold kubelet kubeadm kubectl;  dpkg -i ./some-package.deb
crictl version;  cat /etc/crictl.yaml;  grep -E 'cgroupDriver|containerRuntimeEndpoint' /var/lib/kubelet/config.yaml

Traps

sysctl -w and modprobe are gone after a reboot - it is the files in /etc/sysctl.d and /etc/modules-load.d that last.
A kubelet on cgroupfs with a runtime on systemd (or the other way round) gives an unstable node.
kubeadm's preflight stops at active swap unless the kubelet is configured for it (failSwapOn: false).

Docs

Tasks

Q107 Kernel prerequisites for a Kubernetes node
Q108 The container runtime behind a Pod
Q41 Component versions

4.3 Create and manage Kubernetes clusters using kubeadm

./exam study 4.3 (or kubeadm)

Know

kubeadm init makes the control plane: certificates in /etc/kubernetes/pki, kubeconfigs in /etc/kubernetes, static Pod manifests in /etc/kubernetes/manifests, then CoreDNS and kube-proxy. A CNI plugin is yours to add.
kubeadm join adds a node with a bootstrap token and the hash of the cluster CA; kubeadm token create --print-join-command writes the whole line.
What the cluster was built with is in ConfigMap kubeadm-config (kube-system). kubeadm certs check-expiration lists every certificate it manages.
A static Pod is a manifest in the kubelet's staticPodPath; it shows up in the API as NAME-NODE and can only be changed or removed through the file.

Fast

kubeadm init --pod-network-cidr=10.244.0.0/16 --control-plane-endpoint=HOST:6443
kubeadm token create --ttl 2h --print-join-command;  kubeadm token list
openssl x509 -pubkey -in /etc/kubernetes/pki/ca.crt | openssl rsa -pubin -outform der 2>/dev/null | openssl dgst -sha256 -hex    # the CA hash
kubeadm certs check-expiration;  openssl x509 -in /etc/kubernetes/pki/apiserver.crt -noout -enddate
k -n kube-system get cm kubeadm-config -o yaml
grep staticPodPath /var/lib/kubelet/config.yaml;  k run web --image=nginx:1.27 $do > /etc/kubernetes/manifests/web.yaml

Traps

Tokens expire (24 hours unless you say otherwise) - make a new one rather than hunting for the old.
Check staticPodPath before you write a static Pod: it is not always /etc/kubernetes/manifests.
Deleting a static Pod with kubectl only deletes its mirror; the kubelet puts it straight back.

Docs

Tasks

Q40 kubeadm join token
Q5 Static pod
Q6 Certificates: expiry check and user CSR
Q67 Prepare a node join without shell access to the control plane
Q46 Static pod on a relocated manifest path
Q94 Static Pod on the control plane behind a Service (Simulator Set D (killer.sh-style))
Q95 The kubelet's two certificates (Simulator Set D (killer.sh-style))
Q80 Plan the control-plane upgrade (Simulator Set C)

4.4 Manage the lifecycle of Kubernetes clusters

./exam study 4.4 (or lifecycle)

Know

Upgrade one minor version at a time, control plane first: the kubeadm package, kubeadm upgrade plan and apply, drain, the kubelet and kubectl packages, restart the kubelet, uncordon. Workers: kubeadm upgrade node in place of apply.
Maintenance on a node: kubectl drain cordons it and evicts its Pods; kubectl uncordon gives it back.
etcd: etcdctl snapshot save backs it up; etcdutl snapshot restore --data-dir unpacks a snapshot into a new directory that etcd's manifest must then point at.
kubeadm certs renew all renews the control-plane certificates; the static Pods have to be restarted to load them.

Fast

k drain NODE --ignore-daemonsets --delete-emptydir-data;  k uncordon NODE
apt-get install -y kubeadm='1.36.*';  kubeadm upgrade plan;  kubeadm upgrade apply v1.36.x      # workers: kubeadm upgrade node
apt-get install -y kubelet='1.36.*' kubectl='1.36.*';  systemctl daemon-reload;  systemctl restart kubelet
etcdctl --endpoints=https://127.0.0.1:2379 --cacert=/etc/kubernetes/pki/etcd/ca.crt \
  --cert=/etc/kubernetes/pki/etcd/server.crt --key=/etc/kubernetes/pki/etcd/server.key snapshot save /opt/backup.db
etcdutl snapshot restore /opt/backup.db --data-dir /var/lib/etcd-restore     # then etcd.yaml: the hostPath of volume etcd-data
kubeadm certs renew all;  kubeadm certs check-expiration

Traps

drain stops at DaemonSet Pods (--ignore-daemonsets), at emptyDir data (--delete-emptydir-data) and at bare Pods (--force, which deletes them for good).
A drained node stays cordoned until you uncordon it.
With etcd 3.6, as here, restore exists only in etcdutl - etcdctl snapshot restore is gone.
Restoring etcd takes the whole cluster back to the snapshot: everything created since is lost.

Docs

Tasks

Q109 Drain the control-plane node and bring it back
Q2 etcd snapshot
Q65 Renew control-plane certificates
Q45 etcd restore
Q80 Plan the control-plane upgrade (Simulator Set C)

4.5 Implement and configure a highly-available control plane

./exam study 4.5 (or ha)

Know

Highly available means several control-plane nodes (three as a rule) behind one stable address - the controlPlaneEndpoint, a load balancer or virtual IP, fixed at kubeadm init.
etcd is either stacked (a member on every control-plane node) or external (hosts of its own). It needs a majority to accept writes: 3 members survive the loss of 1, 5 of 2.
More control-plane nodes join with kubeadm join --control-plane --certificate-key KEY; the key comes from kubeadm init phase upload-certs --upload-certs and is good for two hours.
Every kube-apiserver serves at once. Of the schedulers and controller-managers only the leader acts - they elect it through a Lease in kube-system.

Fast

k get nodes -l node-role.kubernetes.io/control-plane
k -n kube-system get cm kubeadm-config -o yaml | grep controlPlaneEndpoint
kubeadm init --control-plane-endpoint=LB:6443 --upload-certs
kubeadm init phase upload-certs --upload-certs                       # prints the certificate key
kubeadm token create --print-join-command --certificate-key KEY      # ... --control-plane --certificate-key KEY
k -n kube-system get lease kube-scheduler kube-controller-manager    # HOLDER = NODE_uuid
etcdctl member list -w table;  etcdctl endpoint status -w table;  etcdctl endpoint health     # with the four etcd flags
k -n kube-system get pods -l component=etcd -o wide

Traps

A cluster initialised without a controlPlaneEndpoint cannot simply be given a second control-plane node.
An even number of etcd members tolerates no more failures than the odd number below it.
The certificate key expires after two hours - upload the certificates again rather than reusing an old key.

Docs

Tasks

Q110 Prepare the join of a second control-plane node
Q111 Who leads, and who is in etcd
Q86 How the control plane is run (Simulator Set D (killer.sh-style))
Q87 Cluster facts to an exact file (Simulator Set D (killer.sh-style))

4.6 Use Helm and Kustomize to install cluster components

./exam study 4.6 (or helmkustomize)

Know

Helm: a chart is the package, a release one installation of it in a Namespace, and each install, upgrade or rollback a revision. Values come from the chart, then -f files, then --set.
helm template renders a chart without installing it; helm show values prints its defaults; helm get values what a release was given.
Kustomize: a kustomization.yaml lists resources and changes them - namespace, namePrefix, labels, images, replicas, patches - and generates ConfigMaps and Secrets. An overlay lists a base and changes only what differs.

Fast

helm repo add NAME URL && helm repo update;  helm search repo NAME --versions
helm install REL CHART -n NS --create-namespace --set replicaCount=2 -f values.yaml       # --version X
helm upgrade REL CHART -n NS --reuse-values --set image.tag=1.27
helm template REL CHART -n NS --set replicaCount=3 > manifest.yaml
helm list -A;  helm history REL -n NS;  helm rollback REL 1 -n NS;  helm uninstall REL -n NS
k kustomize DIR | less;  k apply -k DIR
# kustomization.yaml: resources: [../../base]  namespace: prod  namePrefix: prod-  images: [{name: nginx, newTag: "1.27"}]
#                     replicas: [{name: web, count: 3}]  patches: [{path: patch.yaml}]  configMapGenerator: [{name: cfg, literals: [k=v]}]

Traps

Releases live in a Namespace: without -n Helm looks in default.
An upgrade without --reuse-values (or the same -f and --set again) puts every value back to the chart's default.
In a kustomization, images, replicas and patches use the names of the base, before any prefix.
namespace: in a kustomization does not create the Namespace.

Docs

Tasks

Q21 Helm release install and upgrade
Q3 Kustomize overlay
Q48 Kustomize with generators and patches
Q69 Render a chart, then install it (Simulator Set C)
Q98 Helm release housekeeping (Simulator Set D (killer.sh-style))

4.7 Understand extension interfaces (CNI, CSI, CRI, etc.)

./exam study 4.7 (or interfaces)

Know

CRI: the kubelet drives the container runtime (containerd, CRI-O) through a socket; crictl speaks the same protocol, so it works on a node when kubectl does not.
CNI: for every Pod the runtime calls the plugins named in /etc/cni/net.d (binaries in /opt/cni/bin) to give it an address and wire it up. The plugin - kindnet, Calico, Cilium, Flannel - usually runs as a DaemonSet.
CSI: a storage driver runs as Pods, registers a CSIDriver object, and a StorageClass names it as provisioner.

Fast

k get nodes -o wide                                   # CONTAINER-RUNTIME column
crictl version;  crictl pods;  crictl ps -a;  crictl images;  crictl inspect CONTAINER-ID
grep containerRuntimeEndpoint /var/lib/kubelet/config.yaml;  cat /etc/crictl.yaml
ls /etc/cni/net.d;  cat /etc/cni/net.d/*;  ls /opt/cni/bin
k -n kube-system get ds                               # the CNI's DaemonSet beside kube-proxy
k get csidrivers;  k get csinodes;  k get sc          # PROVISIONER

Traps

Not every CNI plugin enforces NetworkPolicy (Flannel does not; kindnet in this cluster does).
Without a CNI plugin the nodes stay NotReady: cni plugin not initialized.
The runtime takes the first configuration file in /etc/cni/net.d, in alphabetical order.

Docs

Tasks

Q112 CNI, CSI and CRI: what this cluster plugs in
Q108 The container runtime behind a Pod
Q41 Component versions
Q63 Cluster facts, exactly
Q77 Audit the CNI, then lock a namespace down (Simulator Set C)
Q87 Cluster facts to an exact file (Simulator Set D (killer.sh-style))

4.8 Understand CRDs, install and configure operators

./exam study 4.8 (or crds)

Know

A CustomResourceDefinition adds a kind to the API: group, names (kind, plural, singular, shortNames), scope (Namespaced or Cluster) and versions, each with an OpenAPI v3 schema.
The schema validates custom resources - types, required fields, enum, minimum, maximum, defaults - and feeds kubectl explain.
An operator is a CRD plus a controller (a Deployment with RBAC) that acts on those objects. Installing one means applying its manifests or its Helm chart, then creating a custom resource.

Fast

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata: {name: backups.data.example.com}             # PLURAL.GROUP
spec:
  group: data.example.com
  scope: Namespaced
  names: {kind: Backup, plural: backups, singular: backup, shortNames: [bk]}
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              required: [schedule]
              properties:
                schedule: {type: string}
                retention: {type: integer, minimum: 1, default: 7}
k get crd;  k api-resources --api-group=data.example.com;  k explain backup.spec --recursive

Traps

The CRD's name must be PLURAL.GROUP, and exactly one version has storage: true.
A custom resource's apiVersion is GROUP/VERSION of the CRD, not apiextensions.k8s.io/v1.
default and validation only work inside a structural schema: every level needs its type.
Deleting a CRD deletes every object of that kind.

Docs

Tasks

Q4 CustomResourceDefinition
Q34 Discover a CRD field with kubectl explain
Q49 CRD with validation and defaults
Q91 API resources and a Role census (Simulator Set D (killer.sh-style))

Services & Networking (20%)

5.1 Understand connectivity between Pods

./exam study 5.1 (or connectivity)

Know

Every Pod has its own IP address, and any Pod reaches any other Pod on any node at that address without NAT. The CNI plugin makes that true.
Each node hands out Pod addresses from its own range (spec.podCIDR), a slice of the cluster's Pod CIDR; Services get theirs from the separate service CIDR.
A hostNetwork Pod lives in the node's network: it has the node's address and shares its ports.
Containers of one Pod share a network namespace and talk over localhost.

Fast

k get pods -o wide -A;  k get nodes -o custom-columns=NODE:.metadata.name,PODCIDR:.spec.podCIDR,IP:.status.addresses[0].address
k exec POD -- wget -qO- -T3 http://POD-IP:PORT
k -n kube-system get cm kubeadm-config -o yaml | grep -E 'podSubnet|serviceSubnet'
k -n kube-system get pods -o wide | grep -E 'kube-proxy|kindnet';  k -n kube-system get cm kube-proxy -o yaml | grep mode

Traps

A Pod's address changes whenever the Pod is replaced - that is what Services are for.
Reaching a Pod by IP proves the network; reaching it by Service name also needs endpoints and DNS.
If only the Pods of one node are unreachable, look at that node's CNI and kube-proxy Pods.

Docs

Tasks

Q113 Pod to Pod, across nodes
Q63 Cluster facts, exactly
Q71 Expose and verify the dispatch API (Simulator Set C)
Q77 Audit the CNI, then lock a namespace down (Simulator Set C)
Q87 Cluster facts to an exact file (Simulator Set D (killer.sh-style))

5.2 Define and enforce Network Policies

./exam study 5.2 (or netpol)

Know

Pods accept and send everything until a NetworkPolicy selects them. From then on, for the policyTypes it lists, only what some policy allows gets through.
Policies only allow, and they add up: there is no deny rule and no ordering.
Peers: podSelector (same Namespace), namespaceSelector, ipBlock. Two selectors in one list item mean AND; two list items mean OR.
Default deny: podSelector: {} with the policyTypes and no rules. An egress lock-down also has to allow DNS (UDP and TCP 53).

Fast

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata: {name: backend-policy, namespace: NS}
spec:
  podSelector: {matchLabels: {app: backend}}
  policyTypes: [Ingress, Egress]
  ingress:
    - from: [{podSelector: {matchLabels: {app: frontend}}}]
      ports: [{protocol: TCP, port: 8080}]
  egress:
    - to: [{namespaceSelector: {matchLabels: {kubernetes.io/metadata.name: kube-system}}, podSelector: {matchLabels: {k8s-app: kube-dns}}}]
      ports: [{protocol: UDP, port: 53}, {protocol: TCP, port: 53}]
k describe netpol backend-policy -n NS;  k exec CLIENT -- wget -qO- -T2 http://backend:8080

Traps

There is no kubectl create networkpolicy - copy the skeleton from the docs.
namespaceSelector and podSelector in the same item: Pods with that label in those Namespaces. In two items: either.
A missing ingress denies everything; ingress: [{}] allows everything.
A Namespace is matched by its labels; kubernetes.io/metadata.name=NAME is always there.

Docs

https://kubernetes.io/docs/concepts/services-networking/network-policies/

Tasks

Q11 NetworkPolicy
Q42 Egress-only NetworkPolicy
Q54 Zero-trust namespace
Q83 NetworkPolicy for the safety monitor (Simulator Set C)
Q100 Namespace AND pod selector, enforced (Simulator Set D (killer.sh-style))
Q77 Audit the CNI, then lock a namespace down (Simulator Set C)

5.3 Use ClusterIP, NodePort, LoadBalancer service types and endpoints

./exam study 5.3 (or services)

Know

A Service selects Pods by label and forwards port to targetPort - a number, or the name of a container port.
ClusterIP is reachable inside the cluster; NodePort adds a port (30000-32767) on every node; LoadBalancer adds an external address from the cloud; ExternalName is a DNS alias; headless (clusterIP: None) gives every Pod its own DNS record.
The Pods behind a Service are its endpoints, kept in EndpointSlices; only Ready Pods are in them.

Fast

k expose deploy shop --name=shop-svc --port=80 --target-port=80 --type=NodePort
k create svc nodeport shop-svc --tcp=80:80 --node-port=30080           # then check the selector
k create svc externalname legacy --external-name=db.example.com
k get svc,endpointslices -o wide;  k describe svc shop-svc             # Endpoints:
k get pods -l app=shop --show-labels
k run tmp --rm -it --restart=Never --image=busybox:1.36 -- wget -qO- -T3 http://shop-svc

Traps

kubectl expose copies the workload's selector; kubectl create svc selects app=, which may match nothing.
expose cannot choose the nodePort - use create svc nodeport --node-port or edit the YAML.
A LoadBalancer stays where nothing provides one; it still works as a NodePort.
A headless Service for a StatefulSet has to carry the name in the StatefulSet's serviceName.

Docs

Tasks

Q12 NodePort Service
Q30 Named ports
Q43 Headless and ExternalName services
Q64 The context's namespace
Q71 Expose and verify the dispatch API (Simulator Set C)
Q73 Fix ETA service connectivity (Simulator Set C)
Q94 Static Pod on the control plane behind a Service (Simulator Set D (killer.sh-style))

5.4 Use the Gateway API to manage Ingress traffic

./exam study 5.4 (or gateway)

Know

Three kinds, three owners: a GatewayClass names the controller, a Gateway opens listeners (port, protocol, hostname, which routes may attach), an HTTPRoute attaches to a Gateway (parentRefs) and sends requests to Services (backendRefs).
An HTTPRoute rule matches on path, header, method or query, and may split traffic between backends by weight - that is a canary.
The kinds are CRDs (gateway.networking.k8s.io): they have to be installed, and a controller has to implement them.

Fast

apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata: {name: web-gw, namespace: NS}
spec:
  gatewayClassName: example
  listeners: [{name: http, protocol: HTTP, port: 80, hostname: shop.example.com}]
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata: {name: web, namespace: NS}
spec:
  parentRefs: [{name: web-gw}]
  hostnames: [shop.example.com]
  rules:
    - matches: [{path: {type: PathPrefix, value: /}}]
      backendRefs: [{name: v1, port: 80, weight: 90}, {name: v2, port: 80, weight: 10}]
k get gatewayclass,gateway,httproute -A;  k describe httproute web -n NS

Traps

A route in another Namespace attaches only if the listener's allowedRoutes lets it.
A header match belongs in matches, beside or instead of the path - and several rules are tried most specific first.
No Gateway controller runs in this simulator, so these tasks are graded on the objects.

Docs

Tasks

Q22 Gateway API HTTPRoute
Q56 Gateway API canary with header match
Q74 Fleet dashboard canary with Gateway API (Simulator Set C)

5.5 Know how to use Ingress controllers and Ingress resources

./exam study 5.5 (or ingress)

Know

An Ingress routes HTTP(S) by host and path to Services of its own Namespace. It does nothing without an ingress controller, chosen with ingressClassName (an IngressClass names the controller).
Each path has a pathType (Prefix, Exact or ImplementationSpecific) and a backend: service.name plus service.port.number or .name.
TLS: spec.tls lists hosts and the kubernetes.io/tls Secret that holds their certificate.

Fast

k create ingress app-ingress -n NS --class=nginx \
  --rule='shop.example.com/api*=api:8080,tls=shop-tls' --rule='shop.example.com/*=web:80,tls=shop-tls'
openssl req -x509 -nodes -newkey rsa:2048 -days 365 -subj '/CN=shop.example.com' -keyout tls.key -out tls.crt
k create secret tls shop-tls -n NS --cert=tls.crt --key=tls.key
k get ingress,ingressclass -A;  k describe ingress app-ingress -n NS

Traps

In --rule a trailing * means pathType Prefix; without it the path is Exact.
The backend port is the Service's port, not the container's.
No ingress controller runs in this simulator, so Ingress tasks are graded on the object - on the exam, curl it.

Docs

Tasks

Q13 Ingress routing
Q55 TLS Ingress with a generated certificate

5.6 Understand and use CoreDNS

./exam study 5.6 (or coredns)

Know

CoreDNS is a Deployment in kube-system behind the Service kube-dns; its configuration, the Corefile, is in ConfigMap coredns: the kubernetes plugin answers for cluster.local, forward sends the rest upstream.
Names: SVC.NS.svc.cluster.local for a Service, POD.SVC.NS.svc.cluster.local for the Pods of a headless Service.
A Pod's /etc/resolv.conf points at the kube-dns address and lists the search domains that make short names work. dnsPolicy decides: ClusterFirst (default), Default (the node's resolver), None with dnsConfig.

Fast

k -n kube-system get deploy coredns;  k -n kube-system get pods -l k8s-app=kube-dns -o wide
k -n kube-system get svc kube-dns;  k -n kube-system get endpointslices -l k8s-app=kube-dns
k -n kube-system get cm coredns -o yaml;  k -n kube-system edit cm coredns
k -n kube-system logs -l k8s-app=kube-dns;  k -n kube-system rollout restart deploy coredns
k run tmp --rm -it --restart=Never --image=busybox:1.36 -- nslookup kubernetes.default.svc.cluster.local
k exec POD -- cat /etc/resolv.conf

Traps

A typo in the Corefile puts CoreDNS in CrashLoopBackOff - its log names the plugin and the line.
DNS can be broken in several places at once: the Corefile, the Deployment (replicas, image), the kube-dns Service (selector, ports), a NetworkPolicy.
A Pod with dnsPolicy: Default resolves the internet but not cluster names.

Docs

Tasks

Q14 Cluster DNS
Q37 Cluster DNS is broken
Q57 DNS down: three faults
Q101 Resolves everything except the cluster (Simulator Set D (killer.sh-style))

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CKA study guide

Storage (10%)

1.1 Implement storage classes and dynamic volume provisioning

1.2 Configure volume types, access modes and reclaim policies

1.3 Manage persistent volumes and persistent volume claims

Troubleshooting (30%)

2.1 Troubleshoot clusters and nodes

2.2 Troubleshoot cluster components

2.3 Monitor cluster and application resource usage

2.4 Manage and evaluate container output streams

2.5 Troubleshoot services and networking

Workloads & Scheduling (15%)

3.1 Understand application deployments and how to perform rolling update and rollbacks

3.2 Use ConfigMaps and Secrets to configure applications

3.3 Configure workload autoscaling

3.4 Understand the primitives used to create robust, self-healing, application deployments

3.5 Configure Pod admission and scheduling (limits, node affinity, etc.)

Cluster Architecture, Installation & Configuration (25%)

4.1 Manage role based access control (RBAC)

4.2 Prepare underlying infrastructure for installing a Kubernetes cluster

4.3 Create and manage Kubernetes clusters using kubeadm

4.4 Manage the lifecycle of Kubernetes clusters

4.5 Implement and configure a highly-available control plane

4.6 Use Helm and Kustomize to install cluster components

4.7 Understand extension interfaces (CNI, CSI, CRI, etc.)

4.8 Understand CRDs, install and configure operators

Services & Networking (20%)

5.1 Understand connectivity between Pods

5.2 Define and enforce Network Policies

5.3 Use ClusterIP, NodePort, LoadBalancer service types and endpoints

5.4 Use the Gateway API to manage Ingress traffic

5.5 Know how to use Ingress controllers and Ingress resources

5.6 Understand and use CoreDNS

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