Kubernetes - PODs

Step-01: PODs Introduction

• What is a POD ?
• What is a Multi-Container POD?

Step-02: PODs Demo

Get Worker Nodes Status

• Verify if kubernetes worker nodes are ready.

# Get Worker Node Status
kubectl get nodes

# Get Worker Node Status with wide option
kubectl get nodes -o wide

Create a Pod

• Create a Pod

# Template
kubectl run <desired-pod-name> --image <Container-Image> --generator=run-pod/v1

# Replace Pod Name, Container Image
kubectl run my-first-pod --image stacksimplify/kubenginx:1.0.0 --generator=run-pod/v1

• Important Note: Without --generator=run-pod/v1 it will create a pod with a deployment which is another core kubernetes concept which we will learn in next few minutes.
• Important Note:
  • With Kubernetes 1.18 version, there is lot clean-up to kubectl run command.
  • The below will suffice to create a Pod as a pod without creating deployment. We dont need to add --generator=run-pod/v1

kubectl run my-first-pod --image stacksimplify/kubenginx:1.0.0

List Pods

• Get the list of pods

# List Pods
kubectl get pods

# Alias name for pods is po
kubectl get po

List Pods with wide option

• List pods with wide option which also provide Node information on which Pod is running

kubectl get pods -o wide

What happened in the backgroup when above command is run?

1. Kubernetes created a pod
2. Pulled the docker image from docker hub
3. Created the container in the pod
4. Started the container present in the pod

Describe Pod

• Describe the POD, primarily required during troubleshooting.
• Events shown will be of a great help during troubleshooting.

# To get list of pod names
kubectl get pods

# Describe the Pod
kubectl describe pod <Pod-Name>
kubectl describe pod my-first-pod 

Access Application

• Currently we can access this application only inside worker nodes.
• To access it externally, we need to create a NodePort Service.
• Services is one very very important concept in Kubernetes.

Delete Pod

# To get list of pod names
kubectl get pods

# Delete Pod
kubectl delete pod <Pod-Name>
kubectl delete pod my-first-pod

Step-03: NodePort Service Introduction

• What are Services in k8s?
• What is a NodePort Service?
• How it works?

Step-04: Demo - Expose Pod with a Service

• Expose pod with a service (NodePort Service) to access the application externally (from internet)
• Ports
  • port: Port on which node port service listens in Kubernetes cluster internally
  • targetPort: We define container port here on which our application is running.
  • NodePort: Worker Node port on which we can access our application.

# Create  a Pod
kubectl run <desired-pod-name> --image <Container-Image> --generator=run-pod/v1
kubectl run my-first-pod --image stacksimplify/kubenginx:1.0.0 --generator=run-pod/v1

# Expose Pod as a Service
kubectl expose pod <Pod-Name>  --type=NodePort --port=80 --name=<Service-Name>
kubectl expose pod my-first-pod  --type=NodePort --port=80 --name=my-first-service

# Get Service Info
kubectl get service
kubectl get svc

# Get Public IP of Worker Nodes
kubectl get nodes -o wide

• Access the Application using Public IP

http://<node1-public-ip>:<Node-Port>

• Important Note about: target-port
  • If target-port is not defined, by default and for convenience, the targetPort is set to the same value as the port field.

# Below command will fail when accessing the application, as service port (81) and container port (80) are different
kubectl expose pod my-first-pod  --type=NodePort --port=81 --name=my-first-service2     

# Expose Pod as a Service with Container Port (--taret-port)
kubectl expose pod my-first-pod  --type=NodePort --port=81 --target-port=80 --name=my-first-service3

# Get Service Info
kubectl get service
kubectl get svc

# Get Public IP of Worker Nodes
kubectl get nodes -o wide

• Access the Application using Public IP

http://<node1-public-ip>:<Node-Port>

Step-05: Interact with a Pod

Verify Pod Logs

# Get Pod Name
kubectl get po

# Dump Pod logs
kubectl logs <pod-name>
kubectl logs my-first-pod

# Stream pod logs with -f option and access application to see logs
kubectl logs <pod-name>
kubectl logs -f my-first-pod

• Important Notes
  • Refer below link and search for Interacting with running Pods for additional log options
  • Troubleshooting skills are very important. So please go through all logging options available and master them.
  • Reference: https://kubernetes.io/docs/reference/kubectl/cheatsheet/

Connect to Container in a POD

• Connect to a Container in POD and execute commands

# Connect to Nginx Container in a POD
kubectl exec -it <pod-name> -- /bin/bash
kubectl exec -it my-first-pod -- /bin/bash

# Execute some commands in Nginx container
ls
cd /usr/share/nginx/html
cat index.html
exit

• Running individual commands in a Container

kubectl exec -it <pod-name> env

# Sample Commands
kubectl exec -it my-first-pod env
kubectl exec -it my-first-pod ls
kubectl exec -it my-first-pod cat /usr/share/nginx/html/index.html

Step-06: Get YAML Output of Pod & Service

Get YAML Output

# Get pod definition YAML output
kubectl get pod my-first-pod -o yaml   

# Get service definition YAML output
kubectl get service my-first-service -o yaml   

Step-07: Clean-Up

# Get all Objects in default namespace
kubectl get all

# Delete Services
kubectl delete svc my-first-service
kubectl delete svc my-first-service2
kubectl delete svc my-first-service3

# Delete Pod
kubectl delete pod my-first-pod

# Get all Objects in default namespace
kubectl get all