Kubernetes PODs

Step-01: PODs Introduction¶

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

Step-02: PODs Demo¶

Step-02-01: Get Worker Nodes Status¶

Verify if kubernetes worker nodes are ready.

# Configure kubeconfig for kubectl
gcloud container clusters get-credentials <CLUSTER-NAME> --region <REGION> --project <PROJECT-NAME>
gcloud container clusters get-credentials standard-public-cluster-1 --region us-central1 --project kdaida123

# Get Worker Node Status
kubectl get nodes

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

Step-02-02: Create a Pod¶

Create a Pod

# Template
kubectl run <desired-pod-name> --image <Container-Image> 

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

Step-02-03: List Pods¶

Get the list of pods

# List Pods
kubectl get pods

# Alias name for pods is po
kubectl get po

Step-02-04: List Pods with wide option¶

List pods with wide option which also provide Node information on which Pod is running
```
# List Pods with Wide Option
kubectl get pods -o wide
```

Step-02-05: 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

Step-02-06: 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 
Observation:
1. Review Events - thats the key for troubleshooting, understanding what happened

Step-02-07: Access Application¶

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

Step-02-08: 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: Load Balancer Service Introduction¶

What are Services in k8s?
What is a Load Balancer Service?
How it works?

Step-04: Demo - Expose Pod with a Service¶

Expose pod with a service (Load Balancer 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.
Verify the following before LB Service creation
Azure Standard Load Balancer created for Azure AKS Cluster
- Frontend IP Configuration
- Load Balancing Rules

Azure Public IP

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

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

# Get Service Info
kubectl get service
kubectl get svc
Observation:
1. Initially External-IP will show as pending and slowly it will get the external-ip assigned and displayed.
2. It will take 2 to 3 minutes to get the external-ip listed

# Describe Service
kubectl describe service my-first-service

# Access Application
http://<External-IP-from-get-service-output>
curl http://<External-IP-from-get-service-output>

Verify the following after LB Service creation
Google Load Balancer created, verify it.
Verify Backends
Verify Frontends
Verify Workloads and Services on Google GKE Dashboard GCP Console

Step-05: Interact with a Pod¶

Step-05-01: 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/

Step-05-02: Connect to a Container in POD and execute command¶

# 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

Step-05-03: Running individual commands in a Container¶

# Template
kubectl exec -it <pod-name> -- <COMMAND>

# 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

# Delete Pod
kubectl delete pod my-first-pod

# Get all Objects in default namespace
kubectl get all

LOGS - More Options¶

# Return snapshot logs from pod nginx with only one container
kubectl logs nginx

# Return snapshot of previous terminated ruby container logs from pod web-1
kubectl logs -p -c ruby web-1

# Begin streaming the logs of the ruby container in pod web-1
kubectl logs -f -c ruby web-1

# Display only the most recent 20 lines of output in pod nginx
kubectl logs --tail=20 nginx

# Show all logs from pod nginx written in the last hour
kubectl logs --since=1h nginx