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PODS CHEAT SHEET

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 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 - execute the yaml file #kubectl apply/create -f # create - oly on creation # apply - create or update changes on a pod kubectl apply -f ./nginx-pod-1.yaml 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 # .... 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 # 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 # 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 # Standard object's metadata. More info: # https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata # # spec # 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 # 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 this is very useful to understand the resource yaml file: DRY-RUN=client/server/n

May 4, 2025 - 03:06

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

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

- execute the yaml file

#kubectl apply/create -f 
  # create - oly on creation 
  # apply  - create or update changes on a pod
kubectl apply -f ./nginx-pod-1.yaml

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
#  ....

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    
           #      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  
           #      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      
           #      Standard object's metadata. More info:
           #      https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
           #  
           #    spec  
           #      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        
           #      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

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

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": {}
}

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

CHANGING PODS

we can use 2 methods to change pod

### imperative

   kubectl edit pod 

    # 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)

### declerative edit the yaml file of the resource (POD) with wanted values and then execute :

  kubectl apply -f ./changed_nginx-pod.yaml

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 :

### duplicate the pod yaml file

  kubectl get pod  nginx-pod-1 -o yaml > duplicated_nginx-pod-1

### edit value of YAML pod

sed -i 's/containerPort: 80/containerPort: 81/' duplicated_nginx-pod-1

### uply new changes on pod :

kubectl apply -f ./duplicated_nginx-pod-1

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

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

#### 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

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 > -- 
kubectl exec -it nginx-pod-1 -- sh

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 ● 

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

Task2

Create the YAML from the nginx pod created in task 1

 kubectl get pod nginx -o yaml > nginx-new.yaml

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: {}

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
#

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


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)