PODs with YAML

PODs with YAML

2025. 1. 7. 14:14ㆍ쿠버네티스/Kubernetes for the Absolute Beginners

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apiVersion: v1
kind: Pod
metadata:
  name: muapp-pod
  labels:
    app: myapp
    type: front-end
sepc:
  containers:
    name: nginx-container
    image: nginx

1. apiVersion

이 필드는 사용할 쿠버네티스 API 버전을 지정합니다.
예시:
- Pod 생성 시: v1
- Deployment 생성 시: apps/v1
- 기타 버전: extensions/v1beta 등.

2. kind

생성하려는 객체의 유형을 지정합니다.
예시:
- Pod: Pod
- ReplicaSet: ReplicaSet
- Deployment: Deployment
- Service: Service

3. metadata

객체의 메타데이터를 포함합니다.
주요 속성:
- name: 객체 이름 (예: my-app-pod).
- labels: 키-값 쌍으로 구성된 라벨(예: app: my-app). 라벨은 나중에 객체를 필터링하거나 그룹화하는 데 유용합니다.
주의사항:
- 들여쓰기는 YAML에서 중요하며, 속성 간 계층 구조를 올바르게 유지해야 합니다.
- 예를 들어, name과 labels는 metadata의 하위 속성이므로 적절히 들여쓰기해야 합니다.

4. spec

객체의 구체적인 사양을 정의합니다.
Pod 생성 시:
- containers 속성을 사용하여 컨테이너를 정의합니다.
- 컨테이너는 리스트 형식으로 작성되며, 각 컨테이너는 이름(name)과 이미지(image) 속성을 가집니다.

spec:
  containers:
  - name: nginx-container
    image: nginx

Pod 생성 및 확인 명령어

# Pod 생성
kubectl create -f pod-definition.yml
# Pod 목록 확인
kubectl get pods
# Pod 상세 정보 확인
kubectl describe pod <pod-name>

Demo - Pods with YAML

# step 1
vi pod.yaml
####
apiVersion : v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
    tier: frontend
spec:
  containers:
  - name: nginx-container
    image: nginx
  - name: busybox
    image: busybox
# close vi
:wq

# step 2
kubectl apply -f pod.yaml

# pod check
kubectl get pods
kubectl describe pod nginx

coding example

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
    - name: nginx
      image: nginx

apiVersion: v1
kind: Pod
metadata:
  name: postgres
  labels:
    tier: db-tier
spec:
  containers:
    - name: postgres
      image: postgres
      env:
        - name: POSTGRES_PASSWORD
          value: mysecretpassword

Lab solution

How many pods exist on the system ?

kubectl get pods

Create a new pod with the nginx image.

kubectl run --help
kubectl run nginx --image=nginx

What is the image used to create the new pods? You must look at one of the new pods in detail to figure this out

kubectl describe pod [pod name]

# kubectl get pods
NAME            READY   STATUS    RESTARTS        AGE
newpods-4cfzd   1/1     Running   1 (7m42s ago)   24m
newpods-5q26f   1/1     Running   1 (7m42s ago)   24m
newpods-7q8nb   1/1     Running   1 (7m42s ago)   24m
nginx           1/1     Running   0               63s

# kubectl describe pod newpods-4cfzd 
Name:             newpods-4cfzd
Namespace:        default
Priority:         0
Service Account:  default
Node:             controlplane/192.168.251.252
Start Time:       Tue, 07 Jan 2025 04:37:55 +0000
Labels:           tier=busybox
Annotations:      <none>
Status:           Running
IP:               10.42.0.9
IPs:
  IP:           10.42.0.9
Controlled By:  ReplicaSet/newpods
Containers:
  busybox:
    Container ID:  containerd://c5da4445defb1c5f1cd270a859d8184d861f86db0075078db0c490aef827b07f
    Image:         busybox
    Image ID:      docker.io/library/busybox@sha256:2919d0172f7524b2d8df9e50066a682669e6d170ac0f6a49676d54358fe970b5
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      1000
    State:          Running
      Started:      Tue, 07 Jan 2025 04:54:37 +0000
    Last State:     Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Tue, 07 Jan 2025 04:37:56 +0000
      Finished:     Tue, 07 Jan 2025 04:54:36 +0000
    Ready:          True
    Restart Count:  1
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-st8dg (ro)
Conditions:
  Type                        Status
  PodReadyToStartContainers   True 
  Initialized                 True 
  Ready                       True 
  ContainersReady             True 
  PodScheduled                True 
Volumes:
  kube-api-access-st8dg:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age                  From               Message
  ----    ------     ----                 ----               -------
  Normal  Scheduled  24m                  default-scheduler  Successfully assigned default/newpods-4cfzd to controlplane
  Normal  Pulled     24m                  kubelet            Successfully pulled image "busybox" in 266ms (266ms including waiting). Image size: 2167089 bytes.
  Normal  Pulling    7m56s (x2 over 24m)  kubelet            Pulling image "busybox"
  Normal  Created    7m56s (x2 over 24m)  kubelet            Created container busybox
  Normal  Started    7m56s (x2 over 24m)  kubelet            Started container busybox
  Normal  Pulled     7m56s                kubelet            Successfully pulled image "busybox" in 230ms (230ms including waiting). Image size: 2167089 bytes.

Which nodes are these pods placed on?

You must look at all the pods in detail to figure this out.

kubectl describe pod [pod name]

node 카테고리 확인

# kubectl get pods
NAME            READY   STATUS    RESTARTS        AGE
newpods-4cfzd   1/1     Running   1 (7m42s ago)   24m
newpods-5q26f   1/1     Running   1 (7m42s ago)   24m
newpods-7q8nb   1/1     Running   1 (7m42s ago)   24m
nginx           1/1     Running   0               63s

# kubectl describe pod newpods-4cfzd 
Name:             newpods-4cfzd
Namespace:        default
Priority:         0
Service Account:  default
Node:             controlplane/192.168.251.252
Start Time:       Tue, 07 Jan 2025 04:37:55 +0000
Labels:           tier=busybox
Annotations:      <none>
Status:           Running
IP:               10.42.0.9
IPs:
  IP:           10.42.0.9
Controlled By:  ReplicaSet/newpods
Containers:
  busybox:
    Container ID:  containerd://c5da4445defb1c5f1cd270a859d8184d861f86db0075078db0c490aef827b07f
    Image:         busybox
    Image ID:      docker.io/library/busybox@sha256:2919d0172f7524b2d8df9e50066a682669e6d170ac0f6a49676d54358fe970b5
    Port:          <none>
    Host Port:     <none>
    Command:
      sleep
      1000
    State:          Running
      Started:      Tue, 07 Jan 2025 04:54:37 +0000
    Last State:     Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Tue, 07 Jan 2025 04:37:56 +0000
      Finished:     Tue, 07 Jan 2025 04:54:36 +0000
    Ready:          True
    Restart Count:  1
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-st8dg (ro)
Conditions:
  Type                        Status
  PodReadyToStartContainers   True 
  Initialized                 True 
  Ready                       True 
  ContainersReady             True 
  PodScheduled                True 
Volumes:
  kube-api-access-st8dg:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age                  From               Message
  ----    ------     ----                 ----               -------
  Normal  Scheduled  24m                  default-scheduler  Successfully assigned default/newpods-4cfzd to controlplane
  Normal  Pulled     24m                  kubelet            Successfully pulled image "busybox" in 266ms (266ms including waiting). Image size: 2167089 bytes.
  Normal  Pulling    7m56s (x2 over 24m)  kubelet            Pulling image "busybox"
  Normal  Created    7m56s (x2 over 24m)  kubelet            Created container busybox
  Normal  Started    7m56s (x2 over 24m)  kubelet            Started container busybox
  Normal  Pulled     7m56s                kubelet            Successfully pulled image "busybox" in 230ms (230ms including waiting). Image size: 2167089 bytes.

kubectl get pods -o wide

How many containers are part of the pod webapp?

# kubectl get pods -o wide
NAME            READY   STATUS         RESTARTS      AGE     IP           NODE           NOMINATED NODE   READINESS GATES
newpods-4cfzd   1/1     Running        1 (10m ago)   27m     10.42.0.9    controlplane   <none>           <none>
newpods-5q26f   1/1     Running        1 (10m ago)   27m     10.42.0.11   controlplane   <none>           <none>
newpods-7q8nb   1/1     Running        1 (10m ago)   27m     10.42.0.10   controlplane   <none>           <none>
nginx           1/1     Running        0             3m59s   10.42.0.12   controlplane   <none>           <none>
webapp          1/2     ErrImagePull   0             5s      10.42.0.13   controlplane   <none>           <none>

READY 부분 확인, 1/2 컨테이너 2개중 1개만 실행 중이나 총 컨테이너는 2개

What images are used in the new webapp pod?

# kubectl describe pod webapp
Name:             webapp
Namespace:        default
Priority:         0
Service Account:  default
Node:             controlplane/192.168.251.252
Start Time:       Tue, 07 Jan 2025 05:05:09 +0000
Labels:           <none>
Annotations:      <none>
Status:           Pending
IP:               10.42.0.13
IPs:
  IP:  10.42.0.13
Containers:
  nginx:
    Container ID:   containerd://e3821dc9c4684264c2afe70a5568806528e7164fa281e2bb98665d64c5b2fcc8
    Image:          nginx
    Image ID:       docker.io/library/nginx@sha256:42e917aaa1b5bb40dd0f6f7f4f857490ac7747d7ef73b391c774a41a8b994f15
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Tue, 07 Jan 2025 05:05:10 +0000
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-ffmx2 (ro)
  agentx:
    Container ID:   
    Image:          agentx
    Image ID:       
    Port:           <none>
    Host Port:      <none>
    State:          Waiting
      Reason:       ImagePullBackOff
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-ffmx2 (ro)
Conditions:
  Type                        Status
  PodReadyToStartContainers   True 
  Initialized                 True 
  Ready                       False 
  ContainersReady             False 
  PodScheduled                True 
Volumes:
  kube-api-access-ffmx2:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type     Reason     Age                 From               Message
  ----     ------     ----                ----               -------
  Normal   Scheduled  105s                default-scheduler  Successfully assigned default/webapp to controlplane
  Normal   Pulling    105s                kubelet            Pulling image "nginx"
  Normal   Pulled     105s                kubelet            Successfully pulled image "nginx" in 141ms (141ms including waiting). Image size: 72099410 bytes.
  Normal   Created    105s                kubelet            Created container nginx
  Normal   Started    105s                kubelet            Started container nginx
  Warning  Failed     40s (x4 over 104s)  kubelet            Error: ImagePullBackOff
  Normal   Pulling    26s (x4 over 105s)  kubelet            Pulling image "agentx"
  Warning  Failed     26s (x4 over 104s)  kubelet            Failed to pull image "agentx": failed to pull and unpack image "docker.io/library/agentx:latest": failed to resolve reference "docker.io/library/agentx:latest": pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed
  Warning  Failed     26s (x4 over 104s)  kubelet            Error: ErrImagePull
  Normal   BackOff    15s (x5 over 104s)  kubelet            Back-off pulling image "agentx"

containers 부분을 확인

What does the READY column in the output of the kubectl get pods command indicate?

Running Containers in POD / Total Containers in POD

Delete the webapp Pod.

kubectl delete pod webapp

Create a new pod with the name redis and the image redis123. Use a pod-definition YAML file. And yes the image name is wrong!

Name: redis
Image name: redis123
kubectl run redis --image=redis123 --dry-run=client -o yaml > redis.yaml

# kubectl run redis --image=redis123 --dry-run=client -o yaml > redis.yaml
# cat redis.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: redis
  name: redis
spec:
  containers:
  - image: redis123
    name: redis
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

kubectl create -f redis.yaml
- pod/redis created

Now change the image on this pod to redis.

Once done, the pod should be in a running state.

kubectl edit pod redis
kubectl vi redis.yaml
kubectl apply -f redis.yaml
kubectl get pods

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공지사항

아카이브

1. apiVersion

2. kind

3. metadata

4. spec

Pod 생성 및 확인 명령어

Demo - Pods with YAML

coding example

Lab solution

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