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Kubernetes Usefull Notes

Simple Application

Creation

Create, via Deployment, a replica set of webserver exposed via service and ingress

kubectl create -f webserver.yaml

or

kubectl create deployments --image=nginx:alpine webserver
kubectl scale deployments --replicas=3 webserver

Exemple of webserver.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
name: webserver
labels:
    app: nginx
spec:
replicas: 3
selector:
    matchLabels:
    app: nginx
template:
    metadata:
    labels:
        app: nginx
    spec:
    containers:
    - name: nginx
        image: nginx:alpine
        ports:
        - containerPort: 80

So now we have 3 nginx running with the 80 port opened at container level only.

Note: The deployments automatically create a replicaset that manage to mantain the desired replica number

Exposing via Service

For expose the application we have to create e service (svc) that expose the POD (container) port to a (Casually extracted) Static NodePort

kubectl create -f webserver-svc.yaml

or

kubectl create service nodeport --tcp=80 webserver

Example of webserver-svc.yaml

apiVersion: v1
kind: Service
metadata:
name: web-service
labels:
    run: web-service
spec:
type: NodePort
ports:
- port: 80
    protocol: TCP
selector:
    app: nginx

Create a Secret

Create a secret to pull image from a private docker registry

kubectl create secret docker-registry regcred --docker-server=<your-registry-server> --docker-username=<your-name> --docker-password=<your-pword> --docker-email=<your-email>

CheatSheet

kubectl

kubectl drain <node-name> --ignore-daemonsets --grace-period 0 --force --delete-emptydir-data --ignore-errors

kubectl get pods --all-namespaces -o wide --field-selector spec.nodeName=<node-name>

kubectl config set-context --current --namespace=<namespace>
kubectl config use-context <context-name>

eksctl

eksctl upgrade cluster --name <cluster-name>
eksctl upgrade cluster --name <cluster-name> --approve

Edit .yaml:

  • update version
  • update nodeGroup name
# ...
metadata:
  version: '1.20'
# ...
nodeGroups:
  - name: nodegroupName-v20
# ...

Create new nodegroup, cordon and drain the old, delete the old

eksctl create nodegroup --include=nodegroupName-v20 -f <cluster-name>.yaml
kubectl drain <node-name> --ignore-daemonsets --grace-period 0 --force --delete-emptydir-data --ignore-errors

eksctl scale nodegroup --name <nodegroup-name> --nodes-min 1 --nodes-max 3 --nodes 2 --cluster <cluster-name>
eksctl create nodegroup --include=<nodegroup-name> -f kubeflow-ai.yaml