Kubernetes
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Kubernetes
Kubernetes, also known as K8s.
Kubernetes is a container or microservice platform that orchestrates computing, networking, and storage infrastructure workloads.
The Kubernetes Project was open-sourced by Google in 2014 after using it to run production workloads at scale for more than a decade. Kubernetes provides the ability to run dynamically scaling, containerised applications, and utilising an API for management. Kubernetes is a vendor-agnostic container management tool, minifying cloud computing costs whilst simplifying the running of resilient and scalable applications.
k8s
"By the way, if you’re wondering where the name “Kubernetes” came from, it is a Greek word, meaning helmsman or pilot. The abbreviation K8s is derived by replacing the eight letters of “ubernete” with the digit 8." [1]
Download
Download Kubernetes | Kubernetes
https://kubernetes.io/releases/download/
List of container images:
curl -Ls "https://sbom.k8s.io/$(curl -Ls https://dl.k8s.io/release/stable.txt)/release" | grep "SPDXID: SPDXRef-Package-registry.k8s.io" | grep -v sha256 | cut -d- -f3- | sed 's/-/\//' | sed 's/-v1/:v1/'
kubectl install
Install and Set Up kubectl on Linux | Kubernetes
https://kubernetes.io/docs/tasks/tools/install-kubectl-linux/
Download binary:
curl -LO "https://dl.k8s.io/release/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl"
Verify checksum:
curl -LO "https://dl.k8s.io/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl.sha256" echo "$(cat kubectl.sha256) kubectl" | sha256sum --check
Install binary:
sudo install -o root -g root -m 0755 kubectl /usr/local/bin/kubectl
Verify version:
kubectl version --client kubectl version --client --output=yaml
Bash completion:
# should already be installed... apt-get install bash-completion
echo 'source <(kubectl completion bash)' >>~/.bashrc
Aliases:
echo 'alias k=kubectl' >>~/.bashrc echo 'alias k8s=kubectl' >>~/.bashrc echo 'complete -o default -F __start_kubectl k' >>~/.bashrc echo 'complete -o default -F __start_kubectl k8s' >>~/.bashrc
ref: [2]
Kubectl config
.kube/config
Definitions
Basic objects include:
Pod. A group of one or more containers.
Service. An abstraction that defines a logical set of pods as well as the policy for accessing them.
Volume. An abstraction that lets us persist data. (This is necessary because containers are ephemeral—meaning data is deleted when the container is deleted.)
Namespace. A segment of the cluster dedicated to a certain purpose, for example a certain project or team of devs.
Create Simple Bash Pod
kubectl run my-shell --rm -i --tty --image ubuntu -- bash
- my-shell: This ends up being the name of the Deployment that is created. Your pod name will typically be this plus a unique hash or ID at the end.
- --rm: Delete any resources we've created once we detach. When you exit out of your session, this cleans up the Deployment and Pod.
- -i/--tty: The combination of these two are what allows us to attach to an interactive session.
- --: Delimits the end of the kubectl run options from the positional arg (bash).
- bash: Overrides the container's CMD. In this case, we want to launch bash as our container's command
ref [3]
Create simple bash pods in background
kubectl run shell1 --image ubuntu sleep infinity kubectl run shell2 --image ubuntu sleep infinity kubectl run shell3 --image ubuntu sleep infinity
Basic Commands
NODE MANAGEMENT
Get Nodes
Get Nodes:
kubectl get nodes
## Example: # kubectl get nodes NAME STATUS ROLES AGE VERSION ci-2210 Ready <none> 509d v1.22.2 ci-2211 Ready <none> 509d v1.22.2 ci-2212 Ready <none> 509d v1.22.2 ci-4010 NotReady <none> 157d ci-0 Ready control-plane,master 299d v1.22.2
Get Nodes Wide Output
kubectl get nodes -o wide
## Example: # kubectl get nodes -o wide NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME ci-infra-01 Ready <none> 83d v1.22.2 10.x.x.x <none> Ubuntu 20.04.3 LTS 5.4.0-97-generic docker://20.10.18
Get Nodes with Labels
k get nodes --show-labels
## Example: $ kubectl kubectl get nodes --show-labels NAME STATUS ROLES AGE VERSION LABELS ci-infra-01 Ready <none> 83d v1.22.2 beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=ci-infra-01,kubernetes.io/os=linux
Evict Pods from Node
kubectl drain <nodename>
Make Node Unschedulable
kubectl cordon <nodename>
Make Node Scheduable
kubectl uncordon <nodename>
Delete Node
kubectl delete node <nodename>
POD MANAGEMENT
Get Pods
Get Pods (in the default name space)
kubectl get pods
# Example: # kubectl get pods NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES kshell 1/1 Running 0 3d20h 50.0.40.7 uls-ep-essdci45 <none> <none>
Get Pods (more details):
kubectl get pods -o wide
# Example # kubectl get pods -o wide NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES kshell 1/1 Running 0 3d20h 50.0.40.7 uls-ep-essdci45 <none> <none>
Filter for specific pod:
kubectl get pods -o wide | grep <nodename>
To specify a different name space add "-n [namespace]"
kubectl get pods -n MyNamespace
ref [4]
Get Specific Pod Details
kubectl get pod [pod-name]
# Example: # kube get pod kshell NAME READY STATUS RESTARTS AGE kshell 1/1 Running 0 3d20h
Connect to Pod and Run Bash
kubectl exec -it [single-container-pod] -- bash
# example: kubectl exec --stdin --tty shell-demo -- /bin/bash
Get Logs of Pod
kubectl logs [pod-name]
Create Simple Pod from Image
kubectl run my-shell --rm -i --tty --image ubuntu -- bash
# run in background kubectl run my-shell -i --tty --image ubuntu -- bash ctrl+p ctrl+q
Note: "image" is Docker image name
Attach to Simple Pod
kubectl attach my-shell -c my-shell -i -t
kubectl exec my-shell -it -- /bin/bash
Delete Pod
kubectl delete pod [pod-name]
NAME SPACE MANAGEMENT
kubectl create namespace [namespace]
Use name space
kubectl -ns [namespace] ...other_k8_commands...
Set default namespace for commands: [5]
kubectl config set-context --current --namespace=[namespace]
To unset:
kubectl config set-context --current --namespace=""
View current context namespace: [6]
kubectl config view | grep namespace:
# or
kubectl config view -o jsonpath={.contexts[].context.namespace}
CONTEXT MANAGEMENT
ref: https://stackoverflow.com/questions/55373686/how-to-switch-namespace-in-kubernetes
kubectl config set-context gce-dev --user=cluster-admin --namespace=dev kubectl config use-context gce-dev
With aliases:
$ alias kubens='kubectl config set-context --current --namespace ' $ alias kubectx='kubectl config use-context '
// Usage $ kubens kube-system // Switch to a different namespace $ kubectx docker // Switch to separate context
With addons like kubectx & kubens
kubens kube-system
With addon like kubectl-use:
# kubectl use prod Switched to context "prod".
# kubectl use default Switched to namespace "default".
# kubectl use stage kube-system Switched to context "stage". Switched to namespace "kube-system".
With kubie alternative to kubectl: [7]
kubie ctx ...
Create Pod from Yaml
Sample Yaml: (php.yml)
apiVersion: v1
kind: Pod
metadata:
name: nodejsapp-pod
labels:
app: nodejsapp
type: front-end
spec:
containers:
- name: nodejsapp-erp
image: bharathirajutut/erp:1.0
Create pod from Yaml:
kubectl apply -f php.yaml
ref [8]
---
Sample Yaml: (shell-demo.yaml)
apiVersion: v1
kind: Pod
metadata:
name: shell-demo
spec:
volumes:
- name: shared-data
emptyDir: {}
containers:
- name: nginx
image: nginx
volumeMounts:
- name: shared-data
mountPath: /usr/share/nginx/html
hostNetwork: true
dnsPolicy: Default
Create pod from Yaml:
kubectl apply -f https://k8s.io/examples/application/shell-demo.yaml
ref [9]
Get YAML from Object
kubectl get deployment,service,pod yourapp -o yaml --export
kubectl get deploy --all-namespaces -o yaml --export
kubectl get deploy deploymentname -o yaml
kubectl get deploy,sts,svc,configmap,secret -n default -o yaml --export > default.yaml
Get YAML for deployed Kubernetes services? - Stack Overflow https://stackoverflow.com/questions/43941772/get-yaml-for-deployed-kubernetes-services
Sample Pod Configs
More Samples:
Pod - Kubernetes examples https://k8s-examples.container-solutions.com/examples/Pod/Pod.html
Nginx
apiVersion: v1
kind: Pod
metadata:
name: nginx
spec:
containers:
- name: nginx
image: nginx:1.14.2
ports:
- containerPort: 80
kubectl apply -f https://k8s.io/examples/pods/simple-pod.yaml
ref: [10]
Pod Template
Prints one thing, then exits. Template for something bigger.
apiVersion: batch/v1
kind: Job
metadata:
name: hello
spec:
template:
# This is the pod template
spec:
containers:
- name: hello
image: busybox:1.28
command: ['sh', '-c', 'echo "Hello, Kubernetes!" && sleep infinity']
restartPolicy: OnFailure
# The pod template ends here
Busy Box Command
apiVersion: v1
kind: Pod
metadata:
labels:
run: busybox
name: busybox
spec:
containers:
- command:
- /bin/sh
- -c
- |
echo "running below scripts"
i=0;
while true;
do
echo "$i: $(date)";
i=$((i+1));
sleep 1;
done
name: busybox
image: busybox
ref: [11]
Create Kubernetes Cluster
Kill Pods Stuck in Terminating
Likely stuck due to Finalizer. Look for finalizer:
kubectl get pod [POD_NAMENAME] -o yaml
Example:
finalizers: - actions.summerwind.dev/runner-pod
If so, remove the finalizer: [1]
kubectl patch pod [POD_NAME] -p '{"metadata":{"finalizers":null}}'