Kubernetes Architecture¶

Step-01: Why Kubernetes?¶

We need to understand why Kubernetes to be used

Step-02: Kubernetes Architecture¶

We need to understand the Kubernetes Architecture in detail
In addition to that we also need to understand how AWS takes the lead from EKS perspective
How AWS has simplified kubernetes for us?
With AWS EKS, what all things offloaded from us?

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
```

AWS EKS - Elastic Kubernetes Service - Masterclass¶

What happened in the backgroup when above command is run?¶

Kubernetes created a pod
Pulled the docker image from docker hub
Created the container in the pod
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