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ido bistry
ido bistry

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PODS CHEAT SHEET

#40daysofkubernetes #kubernetes #idobistry #k8s

PODS CHEAT SHEET

40 Days of K8s – CKA Challenge (07/40)

@piyushsachdeva

Day 7/40 - Pod In Kubernetes Explained | Imperative VS Declarative Way | YAML Tutorial

this suimmery include of 2 issues :

1. POD - cheat sheet

2. EXERCISE from lecture

1. POD - cheat sheet

CREATE POD

Two Ways To Use KUBCTL to create POD:

1. imperative :

create nginx deployment

kubectl run nginx --image=nginx
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2. declerative :

- create nginx yaml file:

  • #### template pod yaml has :
    • apiVersion
    • kind
    • metadata
    • spec 
# nginx-pod-1.yaml # template pod yaml hasa : apiVersion, kind, metadata, spec apiVersion: v1 kind: Pod metadata: name: nginx-pod-1 labels: name: demo type: frontend spec: containers: - name: nginx-container image: nginx:1.28 resources: limits: memory: "128Mi" cpu: "500m" ports: - containerPort: 80 protocol: TCP
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- execute the yaml file 

#kubectl apply/create -f <file-name> # create - oly on creation  # apply - create or update changes on a pod kubectl apply -f ./nginx-pod-1.yaml
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To get the real values used in yaml file

to cretate a resource (pod,service ... ):

  • command used :

kubectl explain _[api-resouce-type]_

  • api-resouce-type type can be pod/service/deployment/replicaset... 
kubectl api-resources # --> will show all of the resources that this command cover : # kubectl explain pod --recursive # -- > NAME SHORTNAMES APIVERSION NAMESPACED KIND # -- > bindings v1 true Binding # -- > componentstatuses cs v1 false ComponentStatus # -- > configmaps cm v1 true ConfigMap # -- > endpoints ep v1 true Endpoints # -- > events ev v1 true Event # -- > limitranges limits v1 true LimitRange # -- > namespaces ns v1 false Namespace # -- > nodes no v1 false Node # -- > persistentvolumeclaims pvc v1 true PersistentVolumeClaim # -- > persistentvolumes pv v1 false PersistentVolume # -- > pods po v1 true Pod # ....
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so : 

 kubectl explain pod # KIND: Pod # VERSION: v1 #  # DESCRIPTION: # Pod is a collection of containers that can run on a host. This resource is # created by clients and scheduled onto hosts. #  # FIELDS: # apiVersion <string> # APIVersion defines the versioned schema of this representation of an object. # Servers should convert recognized schemas to the latest internal value, and # may reject unrecognized values. More info: # https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources #  # kind <string> # Kind is a string value representing the REST resource this object # represents. Servers may infer this from the endpoint the client submits # requests to. Cannot be updated. In CamelCase. More info: # https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds #  # metadata <ObjectMeta> # Standard object's metadata. More info: # https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata #  # spec <PodSpec> # Specification of the desired behavior of the pod. More info: # https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status #  # status <PodStatus> # Most recently observed status of the pod. This data may not be up to date. # Populated by the system. Read-only. More info: # https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status
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this is very useful to understand the resource yaml file:

DRY-RUN=client/server/none

if we want to create a resource YAML template - we can use : dry-run=client parameter and export (-o) as yaml file

the -o means --(o)utput format and can be yaml or json or text

# create nginx pod kubectl run nginx --image=nginx --restart=Never --port=80 --dry-run=client -o json #kubectl create deployment nginx --dry-run=client --image=nginx --replicas=3 -o yaml # dry-run - will not execute the command  # -o yaml - will output as yaml format # -o json - will output as json format
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JSON :

kubectl run nginx --image=nginx --restart=Never --port=80 --dry-run=client -o json

{ "kind": "Pod", "apiVersion": "v1", "metadata": { "name": "nginx", "creationTimestamp": null, "labels": { "run": "nginx" } }, "spec": { "containers": [ { "name": "nginx", "image": "nginx", "ports": [ { "containerPort": 80 } ], "resources": {} } ], "restartPolicy": "Never", "dnsPolicy": "ClusterFirst" }, "status": {} }
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it is very useful to add pipeline to a new file ( .. > < new-file > ) when using dry-run=client

example inline ...

YAML :

kubectl run nginx --image=nginx --restart=Never --port=80 --dry-run=client -o yaml > run-nginx-template.yaml

apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: run: nginx name: nginx spec: containers: - image: nginx name: nginx ports: - containerPort: 80 resources: {} dnsPolicy: ClusterFirst restartPolicy: Never status: {} # this way, the yaml will be saved inside the yaml file to be executed later.  # so we used to **dry-run** to create a yaml fiel for next deploy of this pod
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CHANGING PODS

we can use 2 methods to change pod

  • ### imperative 
 kubectl edit pod <pod-name> # all of the pods YAML will be displayed in a vi editor and we can set values and save  # if the saved version has invalid fields ( syntax error ) the changes will not be commited # and we cant exit from edit window (vi)
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  • ### declerative edit the yaml file of the resource (POD) with wanted values and then execute : 
 kubectl apply -f ./changed_nginx-pod.yaml
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DUPLICATING PODS YAML/JSON

if we have a running pod - we can use imperative command to duplicate it and magke changes at the side - in an editor for next use withapply :

  1. ### duplicate the pod yaml file 
 kubectl get pod nginx-pod-1 -o yaml > duplicated_nginx-pod-1
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  1. ### edit value of YAML pod 
sed -i 's/containerPort: 80/containerPort: 81/' duplicated_nginx-pod-1
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  1. ### uply new changes on pod : 
kubectl apply -f ./duplicated_nginx-pod-1
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INSPECTING PODS - LOGS , DESCRIBE

there are 2 ways to see PODS logs

1. DESCRIBE -

desct=ribe actually used to probe any META DATA about a pod.

it gives us documentation about thr node that the pod is in , the namespace and other infrastractural data

but it also gives us details about last failing logs

so this is very useful command

#kubectl describe pod < pod-name > kubectl describe pod nginx-pod-1
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describe show us full data about the pod, the namespace , the node etc ...

more then this - we can see last logs of the pod
it is very useful also when we have failover of pod - we ma inspect the last logs that are shown in the desribe output

2. LOGS 

# kubectl logs < pod-name > kubectl logs nginx-pod-1
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  • #### TAIL LOGS : if we want to tail logs (like tail -f) we can use -f flag : 
 kubectl logs -f nginx-pod-1 # idubi@DESKTOP-82998RE  3.12  ~/.../Resources/Day07   Day07 ●  kubectl logs -f nginx-pod-1  ------------------------------------------------------------------------------------------------------ # /docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration # /docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/ # /docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh # 10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf # 10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf # /docker-entrypoint.sh: Sourcing /docker-entrypoint.d/15-local-resolvers.envsh # /docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh # /docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh # /docker-entrypoint.sh: Configuration complete; ready for start up # 2025/05/03 15:41:49 [notice] 1#1: using the "epoll" event method # 2025/05/03 15:41:49 [notice] 1#1: nginx/1.28.0 # 2025/05/03 15:41:49 [notice] 1#1: built by gcc 12.2.0 (Debian 12.2.0-14)  # 2025/05/03 15:41:49 [notice] 1#1: OS: Linux 5.15.167.4-microsoft-standard-WSL2 # 2025/05/03 15:41:49 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1048576:1048576 # 2025/05/03 15:41:49 [notice] 1#1: start worker processes # 2025/05/03 15:41:49 [notice] 1#1: start worker process 33 # 2025/05/03 15:41:49 [notice] 1#1: start worker process 34 # 2025/05/03 15:41:49 [notice] 1#1: start worker process 35 # 2025/05/03 15:41:49 [notice] 1#1: start worker process 36 # 2025/05/03 15:41:49 [notice] 1#1: start worker process 37
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PODS - INTERACTIVE MODE

this is especially useful if we want to look at logs
or probe executions inside the pods container
just like in docker (i)nterac(t)ive mode

#kubectl exec -it < pod-name > -- <command> kubectl exec -it nginx-pod-1 -- sh
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DELETE A POD 

# kubectl delete pod < pod-name > kubectl delete pod nginx-pod-1 # ✘ idubi@DESKTOP-82998RE  3.12  ~/.../Resources/Day07   Day07 ●  kubectl get pods  # NAME READY STATUS RESTARTS AGE # 1st-nginx 1/1 Running 0 8h # nginx-pod-1 1/1 Running 2 (8h ago) 8h # idubi@DESKTOP-82998RE  3.12  ~/.../Resources/Day07   Day07 ●  kubectl delete pod 1st-nginx # pod "1st-nginx" deleted # idubi@DESKTOP-82998RE  3.12  ~/.../Resources/Day07   Day07 ●  kubectl get pods  # NAME READY STATUS RESTARTS AGE # nginx-pod-1 1/1 Running 2 (8h ago) 8h # idubi@DESKTOP-82998RE  3.12  ~/.../Resources/Day07   Day07 ● 
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EXERCISE :

Task 1

  • Create a pod using the imperative command and use nginx as the image 
kubectl run nginx --image=nginx --restart=Never --port=80
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Task2

  • Create the YAML from the nginx pod created in task 1 
 kubectl get pod nginx -o yaml > nginx-new.yaml
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  • Update the pod name in the YAML 
sed -i 's/name: nginx/name: nginx-new/' nginx-new.yaml cat nginx-new.yaml|grep -C 3 'name: nginx' # vagrant@master-node:~/temp$ cat nginx-new.yaml|grep -C 3 'name: nginx' # creationTimestamp: "2025-05-04T00:22:22Z" # labels: # run: nginx # name: nginx-new # namespace: default # resourceVersion: "249909" # uid: 7b44db2b-0ca3-4813-9740-494d9287e7ad # -- # containers: # - image: nginx # imagePullPolicy: Always # name: nginx-new # ports: # - containerPort: 81 # protocol: TCP # -- # image: docker.io/library/nginx:latest # imageID: docker.io/library/# nginx@sha256:c15da6c91de8d2f436196f3a768483ad32c258ed4e1beb3d367a27ed67253e66 # lastState: {} # name: nginx-new # ready: true # restartCount: 0 # started: true #  sed -i 's/containerPort: 80/containerPort: 81/' nginx-new.yaml cat nginx-new.yaml|grep -C 3 port # vagrant@master-node:~/temp$ cat nginx-new.yaml|grep -C 3 port # - image: nginx # imagePullPolicy: Always # name: nginx # ports: # - containerPort: 81 # protocol: TCP # resources: {}
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  • Use that YAML to create a new pod with the name nginx-new. 
kubectl apply -f ./nginx-new.yaml # vagrant@master-node:~/temp$ kubectl get pods # NAME READY STATUS RESTARTS AGE # nginx 1/1 Running 0 19m # vagrant@master-node:~/temp$ kubectl apply -f ./ # duplicate-nginx-1.json duplicate-nginx-1.yaml nginx-new.yaml nginx-pod-1.yaml # vagrant@master-node:~/temp$ kubectl apply -f ./nginx-new.yaml # pod/nginx-new created # vagrant@master-node:~/temp$ kubectl get pods # NAME READY STATUS RESTARTS AGE # nginx 1/1 Running 0 20m # nginx-new 1/1 Running 0 28s #
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Task3

  • Apply the below YAML and fix the errors, including all the commands that you run during the troubleshooting and the error message 
apiVersion: v1 kind: Pod metadata: labels: app: test name: redis spec: containers: - image: rediss name: redis
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 echo "apiVersion: v1 kind: Pod metadata: labels: app: test name: redis spec: containers: - image: rediss name: redis" > failed-redis.yaml kubectl apply -f ./failed-redis.yaml ![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/95ecud0130t9jwo422zg.png) kubectl get pods # vagrant@master-node:~/temp$ kubectl get pdos # error: the server doesn't have a resource type "pdos" # vagrant@master-node:~/temp$ kubectl get pods # NAME READY STATUS RESTARTS AGE # nginx 1/1 Running 0 24m # nginx-new 1/1 Running 0 4m33s # redis 0/1 ImagePullBackOff 0 85s kubectl logs redis #vagrant@master-node:~/temp$ kubctl logs redis #-bash: kubctl: command not found #vagrant@master-node:~/temp$ kubectl logs redis #Error from server (BadRequest): container "redis" in pod "redis" is #waiting to start: trying and failing to pull image kubectl describe pod redis ![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/7vwd3dtn85g1ni4wjdx5.png) # vagrant@master-node:~/temp$ kubectl describe pod redis # Name: redis # Namespace: default # Priority: 0 # Service Account: default # Node: worker-node-1/192.168.133.167 # Start Time: Sun, 04 May 2025 00:45:05 +0000 # Labels: app=test ... ---- ------- ---- ------- ---- ------- ... # Normal Scheduled 2m21s default-scheduler Successfully assigned default/redis to # worker-node-1 # Normal Pulling 59s (x4 over 2m21s) kubelet Pulling image "rediss" # Warning Failed 57s (x4 over 2m19s) kubelet Failed to pull image "rediss": failed to pull # and unpack image "docker.io/library/rediss:latest": failed to resolve reference "docker.io/library/# rediss:latest": pull access denied, repository does not exist or may require authorization: server message: # insufficient_scope: authorization failed # Warning Failed 57s (x4 over 2m19s) kubelet Error: ErrImagePull # Normal BackOff 3s (x8 over 2m19s) kubelet Back-off pulling image "rediss" # Warning Failed 3s (x8 over 2m19s) kubelet Error: ImagePullBackOff #  kubectl edit pod redis # change rediss --> redis # --> CTRL+x kubectl get pod redis # vagrant@master-node:~/temp$ kubectl get pod redis # NAME READY STATUS RESTARTS AGE # redis 1/1 Running 0 15m ![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/hqaowcbof5cm9cptqrvp.png)
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