Kubernetes

kubernetes

Components

Pod

Collections of containers collocated in a single machine

Service

Load balancer that can bring traffic to a collection of pods

Deployment

Replicate a container for availability or scale.

Kubelet

The primary node agent that runs on each node.

Basic Commands

create deployment:

kubectl create -f helloworld-pod-with-labels.yml

get pods:

kubectl get pods

get pods with labels:

kubectl get pods --show-labels

rename label:

kubectl label pod/helloworld app=helloworldapp --overwrite

delete label:

kubectl label pod/helloworld app-

selectors:

  kubectl get pods --selector env=production --show-labels
  kubectl get pods --selector dev-lead=jorge,env=staging --show-labels
  kubectl get pods --selector dev-lead!=jorge,env=staging --show-labels
  kubectl get pods -l 'release-version in (1.0,2.0)' --show-labels

delete pods with label:

kubectl delete pods -l dev-lead=jorge

replace service:

kubectl replace --force -f commerce.yaml

deployments:

kubectl set image deployments/commerce commerce-app=jorgecontreras/commerce:0.8 --v 6
kubectl rollout history deployments commerce
kubectl describe deployments commerce
kubectl rollout undo deployment commerce --to-revision=2

scale:

kubectl scale --replicas=10 deployment commerce

(GKE) resize cluster size:

gcloud container clusters resize monarca --num-nodes=3

Imperative approach

$ kubectl create namespace ckad
$ kubectl run nginx --image=nginx --restart=Never -n ckad
$ kubectl edit pod/nginx -n ckad

Declarative approach

Suitable for more elaborate changes, version controlled.

$ vim niginx-pod.yaml
$ kubectl create -f nginx-pod.yaml
$ kubectl delete pod/nginx

Hybrid approach

$ kubectl run nginx --image=nginx --restart=Never --dry-run -o yaml > nginx-pod.yaml
$ vim niginx-pod.yaml
$ kubectl apply -f nginx-pod.yaml

CKAD

Core Concepts

Creating a pod and inspecting it

1. Create the namespace ckad-prep

kubectl create ns ckad-prep

1. In the namespace ckad-prep create a new Pod named mypod with the image nginx:2.3.5. Expose port 80

kubectl run mypod --image=nginx:2.3.5 --restart=Never --port=80 -n ckad-prep

1. Identify the issue with creating the container. Write down the root cause of issue in a file named pod-error.txt

kubectl describe pod mypod -n ckad-prep

1. Change the image of the Pod to nginx:1.15.12

kubectl edit pod mypod -n ckad-prep

1. List the Pod and ensure that the container is running

kubectl get pods -n ckad-prep

1. Log into the container and run the ls command. Write down the output. Logout of the container.

kubectl exec mypod -it -n ckad-prep -- /bin/sh

1. Retrieve the IP address of the Pod mypod

kubectl get pods -n ckad-prep -o wide

1. Run a temporary Pod using the image busybox, shell into it and run a wget command against the nginx Pod using port 80

kubectl run busybox --image=busybox --restart=Never --rm -it -- wget -O- <NGINX-POD-IP>:80

1. Render the logs of Pod mypod

kubectl logs mypod -n ckad-prep

1. Delete the Pod and the namespace

kubectl delete ns ckad-prep

ConfigMaps

1. Create a new file named config.txt with the following environment variables as key/value pairs on each line.
   • DB_URL localhost:3306
   • DB_USERNAME postgres

vim config.txt

1. Create a new ConfigMap named db-config from that file

kubectl create configmap db-config --from-env-file=config.txt

1. Create a Pod names backend that uses the environment variables from the ConfigMap and runs the container with the image nginx

kubectl run backend --image=nginx --restart=Never -o yaml --dry-run=client > backend.yaml

vim backend.yaml

Insert the envFrom section:

envFrom:
    - configMapRef:
        name: db-config

kubectl create -f backend.yaml

1. Shell into the Pod and print out the created environment variables. You should find DB_URL and DB_USERNAME with their appropriate values.

kubectl exec backend -it -- /bin/sh

$ env

Configuring a Pod to use a secret

1. Create a new secret named db-credentials with the key/value pair db-password=passwd

kubectl create secret generic db-credentials --from-literal=db-password=passwd

1. Create a Pod named backend that uses the Secret as environment variable named DB_PASSWORD and runs the container with the image nginx

kubectl run backend --image=nginx --restart=Never --dry-run=client -o yaml > backend.yaml

vim backend.yaml

env:
      - name: DB_PASSWORD
        valueFrom:
          secretKeyRef:
            name: db-credentials
            key: db-password

1. Shell into the Pod and print out the created environment variables. you should find DB_PASSWORD variable.

kubectl exec -it backend -- /bin/sh

env