Kubernetes Notes

Kubernetes Notes:
=======================

1. Kubectl get nodes

2. kubectl get nodes -o wide

Object 1 : POD
=============================
Create a file Pod-defitnion.yml

apiVersion: v1
kind: Pod
metadata:
 name: pod1
 labels:
  app: java
  author: sonal
spec:
 containers:
  - image: nginx
    name: c1


# kubectl create -f Pod-defitnion.yml


# kubectl get pods

# kubectl describe pod pod1 | less


Object 2 : ReplicasSet
===========================



ReplicaSet
A ReplicaSet's purpose is to maintain a stable set of replica Pods running at any given time.

As such, it is often used to guarantee the availability of a specified number of identical Pods.

A ReplicaSet is defined with fields, including

a selector that specifies how to identify Pods it can acquire,
a number of replicas indicating how many Pods it should be maintaining,
and a pod template specifying the data of new Pods it should create to meet the number of replicas criteria.
A ReplicaSet then fulfills its purpose by creating and deleting Pods as needed to reach the desired number. When a ReplicaSet needs to create new Pods, it uses its Pod template.

LAB Execution Steps:
Step1:

Delete all exisitng Pods
kubectl delete pods --all

Step2:

Create Replicas using ReplicaSet YAML file
kubectl create -f https://raw.githubusercontent.com/Sonal0409/Container-Orchestration-using-Kubernetes/main/Day2-Notes/ReplicaSet-Demo/ReplicaSet.yml

Step3:

Validate the creation of Replicas
kubectl get all

kubectl get pods

kubectl get pods -o wide

Scale up the replicas for the current replicaSet
kubectl scale --replicas=5 replicaset myrs

kubectl get pods -o wide

Scale down the replicas for the current replicaSet
kubectl scale --replicas=2 replicaset myrs

kubectl get pods -o wide

Delete Replicaset
kubectl delete replicaset myrs

==================================================================

Lab execution steps:
Execute below steps:

Create the deployment object and Nodeport service:
kubectl create -f https://raw.githubusercontent.com/Sonal0409/Container-Orchestration-using-Kubernetes/main/Day2-Notes/Deployment/deployment.yml

Validate:
kubectl get all

kubectl get deployment kubeserve -o wide

kubectl set image deploy kubeserve app=leaddevops/kubeserve:v2

kubectl rollout status deploy kubeserve

kubectl get all

kubectl get deployment kubeserve -o wide

kubectl set image deploy kubeserve app=leaddevops/kubeserve:v3

lets rollback to older version of image:
kubectl rollout undo deploy kubeserve

Delete the deployment:
kubectl delete deploy kubeserve

kubectl get all



===================================================

Step 1: Run the below pod with multiple containers:

kind: Pod  # kubectl api-resources
apiVersion: v1
metadata:
  name: multi-cont-pod1
  namespace: default
  labels:  # are mandatory # helps to indentify a group of pods in cluster # in kube if you do not provide a label kube will assing one automatically
    role: dev  # here both key & value are your choice
spec:
  #restrtPolicy: Always # Never
  containers:
    - name: cont1
      image: httpd
    - name: cont2
      image: nginx
    - name: ucont
      image: ubuntu


# kubectl create -f multi-containerpod.yml
# kubectl get pods

You will see that only one container is up and rinning, 2 containers have failed

# kubectl describe pod multi-cont-pod1

You will see that cont 2 and ucont have failed and kubernetes(pod) tried to 
restart the containers again and again due to restart policy as Always

Now check the logs for error of cont2

kubectl logs multi-cont-pod1 -c cont2

Now check logs for error of ucont

No logs will be there

**************************************

Now lets correct the YAMl


Instead of nginx, lets take tomcat image and second container as it has different port number

and lets pass a command with ubuntu container, that will invoke a process in the container

command: ["bash", "-c", "sleep 6000"]  

Invoke the bash shell process and run a specific command as sleep 6000, 
which means we are running a specific sleep process in the ubuntu container this time


Create a new YAML file:

# vim multi-containerpod2.yml

kind: Pod  # kubectl api-resources
apiVersion: v1
metadata:
  name: multi-cont-pod2
  namespace: default
  labels:  # are mandatory # helps to indentify a group of pods in cluster # in kube if you do not provide a label kube will assing one automatically
    role: dev  # here both key & value are your choice
spec:
  #restrtPolicy: Always # Never
  containers:
    - name: cont1
      image: httpd
    - name: cont2
      image: tomcat
    - name: ucont
      image: ubuntu
      command: ["bash", "-c", "sleep 6000"]


# kubectl create -f multi-containerpod2.yml

# kubectl get pods

===================================================

Springboot and Mongo DB deployment:

---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: mongodb
  name: mongodb
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongodb
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: mongodb
    spec:
      containers:
       - image: lerndevops/samples:mongodb
         name: mongo

---
apiVersion: v1
kind: Service
metadata:
   name: mongo
spec:
   type: ClusterIP
   ports:
    - port: 27017
      targetPort: 27017
   selector:
     app: mongodb

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: springboot-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - image: lerndevops/samples:springboot-app
        name: springboot-app

---
apiVersion: v1
kind: Service
metadata:
  name: springboot-app-svc
spec:
  type: NodePort
  ports:
   - port: 80
     targetPort: 8080
  selector:
    app: myapp