Kubernetes and Helm (and other stuff)

Kubernetes and Helm (and other stuff)

Kubernetes Articles

https://medium.com/google-cloud/kubernetes-101-pods-nodes-containers-and-clusters-c1509e409e16
Kuberenetes with Nana https://www.youtube.com/watch?v=s_o8dwzRlu4&list=PLXUDioG7XwE59TfSXWN-nDWiTlT5RwrZL&index=56&t=882s
Kubernetes crash loop backoff with some nice utilities for logs etc - https://sysdig.com/blog/debug-kubernetes-crashloopbackoff/
Remote Debug kubernetes pod with Intellij or VSCode - https://refactorfirst.com/how-to-remote-debug-java-application-on-kubernetes
- Also see the quarkus remote Dev stuff on quarkus page - java-quarkus

Kubernetes Tools - Basic list

https://k9scli.io/ home with cheatsheets instructions etc.
- Installing - https://github.com/derailed/k9s#installation
  - On Ubuntu can install easily via webinstall (see page above for details)
VSCode extension - https://marketplace.visualstudio.com/items?itemName=ms-kubernetes-tools.vscode-kubernetes-tools
Lens - discounted due to licensing and shenanigans around the open source version currently -> to be rechecked at some point
Validation tools
- Basic yaml linter - https://yamllint.readthedocs.io/en/stable/
- Kube and helm chart linter - https://docs.kubelinter.io/#/
- Detect old dependencies - https://github.com/FairwindsOps/pluto
Diagrams - https://github.com/mingrammer/diagrams
- Python based tool to generate diagrams from code
- Can generate kubernetes diagrams really easily
https://k8studio.io/ - K8s studio - todo - check this out
- NB Licence free for personal use but paid for PRO

Kubectl and Kustomize

Kustomize - Way of customizing kubernetes config files without templates - https://kubectl.docs.kubernetes.io/guides/introduction/kustomize/
Kubectl - command line of kubernetes - https://kubectl.docs.kubernetes.io/guides/introduction/kubectl/

Microcks - testing with Kubernetes

https://www.linkedin.com/pulse/how-microcks-fit-unify-inner-outer-loops-cloud-native-kheddache/

Kubernetes Notes

Kubernetes Overview

Container Orchestration tool
Google originally developed it
basic tutorial https://kubernetes.io/docs/tutorials/kubernetes-basics/
https://kubernetes.io/docs/concepts/overview/components/

Components

Pods - https://kubernetes.io/docs/concepts/workloads/pods/
- Managing workloads - https://kubernetes.io/docs/concepts/workloads/management/
Deployment -> Replica Set -> Pod
- Favour Deployment over directly using a replica set since you can give declarative updates to your pods
  - https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
  - Deployment describes a desired state (in the yaml spec: section) and the Deployment Controller changes actual state to reflect desired state.
  - Replica Set aims to maintain a stable set of replica Pods running at any given time https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/.
- Restarting Pods
  - listing of a few methods
    - https://spacelift.io/blog/restart-kubernetes-pods-with-kubectl
Operator Pattern - https://kubernetes.io/docs/concepts/extend-kubernetes/operator/
- https://www.redhat.com/en/topics/containers/what-is-a-kubernetes-operator
- https://www.cncf.io/blog/2022/06/15/kubernetes-operators-what-are-they-some-examples/
Custom Resources - https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/

Kubernetes commands

Kubernetes Cheatsheet - https://kubernetes.io/docs/reference/kubectl/cheatsheet/

# kubectl but my alias is "k"

# Listing stuff
kubectl get pods --all-namespaces            # list pods in all namespaces not just the current one
k get pods -n kubernetes-system              # List pods in a given namespace
kubectl get pods -o wide                     # Get a lot more details
kubectl get pods -w                          # Watch (useful waiting for stuff to get running)
kubectl get pods -l some-label                # List pods with a given label
kubectl get pods -l some-label --show-labels  # Show the labels

# Adding a label
kubectl label pod <somepodname> <somelabel>=true

# all running services - get the ports!
kubectl get service --all-namespaces

# all images inside the K3S cluster (but again Lens will probably be better for it)
docker exec k3d-k3s-default-server-0 sh -c "ctr image list"
  

Admin stuff

# Create a namespace
kubectl create namespace <namespace_name>

# Creating a rolebinding for a service account
kubectl create rolebinding -n "<somens>" edit --clusterrole=edit --serviceaccount="<somens>":<someaccount>

# Running a command as a service account or some other user to see if it is possible
kubectl --as=system:serviceaccount:"$NS":$SA auth can-i use

# kube-apiserver command
kubectl exec -it -n kube-system kube-apiserver-kind-control-plane -- kube-apiserver -h
  

Debug - run as another user - https://kubernetes.io/docs/reference/access-authn-authz/authentication/#user-impersonation

Getting a shell to a running container

https://kubernetes.io/docs/tasks/debug/debug-application/get-shell-running-container/

# Basic form
kubectl exec --stdin --tty shell-demo -- /bin/bash
  

Inter pod communication

https://www.tutorialworks.com/kubernetes-pod-communication/
- THis is part of the learning list so I'll add notes here once done
https://kubernetes.io/docs/concepts/services-networking/connect-applications-service/
https://dev.to/narasimha1997/communication-between-microservices-in-a-kubernetes-cluster-1n41

K9s Useful Commands

https://k9scli.io/topics/commands/ list of commands
https://blog.palark.com/k9s-the-powerful-terminal-ui-for-kubernetes/ nice tutorial with plenty of examples

K9s Commands cheatsheet

The ":" is used as a command prefix and then can be followed by a command
- :pods - see pods
- :svc - see services
- :deploy - see deployments
- :sts - see stateful sets
- :rs - see replica sets
- :ns - see namespaces
- :no - see nodes
- :sec - see secrets
- :cm - config maps
:xray -> different views of the cluster with a tree layout

Simple yaml for a pod

From this page https://downey.io/notes/dev/ubuntu-sleep-pod-yaml/
Pod sleeps for a week
- Save to a file called ubuntu.yaml
- create with - kubectl apply -f ubuntu.yaml
- connect with - kubectl exec -it ubuntu -- /bin/bash

apiVersion: v1
kind: Pod
metadata:
  name: ubuntu
  labels:
    app: ubuntu
spec:
  containers:
  - image: ubuntu
    command:
      - "sleep"
      - "604800"
    imagePullPolicy: IfNotPresent
    name: ubuntu
  restartPolicy: Always
  

Helm

Customizing the configmap name generated - ChatGPT question - "research helm, when installing a helm chart which creates a configmap, the configmap is always named with the namespace and release name but I want only the release name"

Configmaps in helm

https://stackoverflow.com/questions/69837364/helm-configmap-in-values-yaml