Kubernetes commands for yamls

In this tutorial, we will explore some of the most important and basic Kubernetes commands for yamls

For Kubernetes 1.18 & above Versions Only

Kubernetes commands to generate Pod Yamls

Generate pod yaml file

ubuntu@lb:~$ kubectl run nginx --image=nginx --dry-run=client -o yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
ubuntu@lb:~$

Generate pod yaml file with restartPolicy: Never

ubuntu@lb:~$ kubectl run nginx --image=nginx --restart=Never --dry-run=client -o yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}
ubuntu@lb:~$

Generate pod yaml file with labels app=web and env=dev

ubuntu@lb:~$ kubectl run nginx --image=nginx -l="app=web,env=dev" --dry-run=client -o yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    app: web
    env: dev
  name: nginx
spec:
  containers:
  - image: nginx
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
ubuntu@lb:~$

Generate pod yaml with env variables env hello=world and me=aarav

ubuntu@lb:~$ kubectl run nginx --image=nginx --env="hello=world" --env="me=aarav" --dry-run=client -o yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - env:
    - name: hello
      value: world
    - name: me
      value: aarav
    image: nginx
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}
ubuntu@lb:~$

Generate pod yaml with below parameters:

• env variable hello=world
• labels app=web
• cpu limit 200m
• memory 250Mi
• Pod should restart on Failure

ubuntu@lb:~$ kubectl run nginx --image=httpd --restart=OnFailure --env="hello=world" -l="app=web" --limits="cpu=200m,memory=150Mi" --dry-run=client -o yaml
Flag --limits has been deprecated, has no effect and will be removed in 1.24.
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    app: web
  name: nginx
spec:
  containers:
  - env:
    - name: hello
      value: world
    image: httpd
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: OnFailure
status: {}
ubuntu@lb:~$

Generate pod yaml file & Service yaml file together

ubuntu@lb:~$ kubectl run nginx --image=nginx --port=80 --expose --dry-run=client -o yaml
apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  name: nginx
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    run: nginx
status:
  loadBalancer: {}
---
---
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: Always
status: {}
ubuntu@lb:~$

Create Pod

## Note: remove --dry-run -o yaml from all above commands to create pods ex as below. 

ubuntu@lb:~$ kubectl run nginx --image nginx
pod/nginx created
ubuntu@lb:~$ kubectl get pods
NAME    READY   STATUS    RESTARTS   AGE
nginx   1/1     Running   0          9s
ubuntu@lb:~$

Kubernetes commands to Generate Deployment Yamls

ubuntu@lb:~$ kubectl create deployment apache --image httpd --dry-run=client -o yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: apache
  name: apache
spec:
  replicas: 1
  selector:
    matchLabels:
      app: apache
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: apache
    spec:
      containers:
      - image: httpd
        name: httpd
        resources: {}
status: {}
ubuntu@lb:~$

Deployments

ubuntu@lb:~$ kubectl create deployment apache --image httpd
deployment.apps/apache created
ubuntu@lb:~$

##Verify the deployment

ubuntu@lb:~$ kubectl get deploy
NAME     READY   UP-TO-DATE   AVAILABLE   AGE
apache   1/1     1            0           11s
ubuntu@lb:~$


## List the pods of the nginx deployment
ubuntu@lb:~$ kubectl get pods
NAME                     READY   STATUS    RESTARTS   AGE
apache-6d96f8c8d-72zw9   1/1     Running   0          17s
nginx                    1/1     Running   0          3m50s
ubuntu@lb:~$
 

Scale deployment named apache to 3 replicas

ubuntu@lb:~$ kubectl scale deploy apache --replicas=3
deployment.apps/apache scaled


## List the deployment
ubuntu@lb:~$ kubectl get deploy
NAME     READY   UP-TO-DATE   AVAILABLE   AGE
apache   3/3     3            3           4m43s

## List the pods for apache deployment
ubuntu@lb:~$ kubectl get pods
NAME                     READY   STATUS    RESTARTS   AGE
apache-6d96f8c8d-2bm9d   1/1     Running   0          107s
apache-6d96f8c8d-686hp   1/1     Running   0          107s
apache-6d96f8c8d-72zw9   1/1     Running   0          6m16s

Replication Controller

Create a replication controller named Tomcat

 vim replicaton-ctrl.yml 

 kubectl create -f replicaton-ctrl.yml --dry-run=client -o yaml
apiVersion: v1
kind: ReplicationController
metadata:
  name: tomcat
  namespace: default
spec:
  replicas: 3
  selector:
    app: tomcat
  template:
    metadata:
      labels:
        app: tomcat
      name: tomcat
    spec:
      containers:
      - image: tomcat
        name: tomcat-cont
        ports:
        - containerPort: 8080

kubectl create -f replicaton-ctrl.yml
##List the replication contoller
kubectl get rc                        
NAME     DESIRED   CURRENT   READY   AGE
tomcat   3         3         3       4m24s

Scale Replication controller

kubectl scale rc tomcat --replicas 5
replicationcontroller/tomcat scaled
## List rc
kubectl get rc tomcat
NAME     DESIRED   CURRENT   READY   AGE
tomcat   5         5         5       7m46s

Replicasets

Create a Replicaset named httpd

vi rs.yml
apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: httpd
spec:
  replicas: 3
  selector:
    matchLabels:
      tier: frontend
  template:
    metadata:
      labels:
        tier: frontend
    spec:
      containers:
      - name: rep1
        image: httpd

┌──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl create -f rs.yml                                                               
replicaset.apps/httpd created

##List the replicasets
┌──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl get rs
NAME    DESIRED   CURRENT   READY   AGE
httpd   3         3         3       2m3s

Scale the replicaset to 5

┌──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl scale rs httpd --replicas 5                                                  
replicaset.apps/httpd scaled

##List replicasets
┌──(ved㉿lb)-[~]
└─$ kubectl get rs httpd
NAME    DESIRED   CURRENT   READY   AGE
httpd   5         5         5       3m2s

Statefulsets

Create a Statefulset

(ved㉿lb)-[~/kuber-yamls]└─$ vim statefulset.yml

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: nginx
spec:
  replicas: 2
  serviceName: nginx
  selector:
      matchLabels:
        app: web

  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
        - name: nginx-cont
          image: nginx
          ports:
          - containerPort: 8080

┌──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl create -f statefulset.yml                         
statefulset.apps/nginx created

#List the statefulsets
┌──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl get statefulsets
NAME    READY   AGE
nginx   2/2     53s

Scale statefulesets to 5

──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl scale statefulsets nginx --replicas=5
statefulset.apps/nginx scaled

#List the statefulsets after scaling
┌──(ved㉿lb)-[~/kuber-yamls]
└─$ kubectl get statefulset nginx
NAME    READY   AGE
nginx   5/5     4m4s

Conclusion

We have explore different Kubernetes imperative command and Declarative yaml in this tutorial. Stay tuned for more K8’s.