664 lines
15 KiB
Markdown
664 lines
15 KiB
Markdown
# kubernetes
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Kubernetes is an open‑source platform that automates the deployment, scaling, and management of containerized applications. It acts as an orchestrator, ensuring your containers run reliably across clusters of machines, handling networking, storage, and updates without downtime.
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- [Namespaces](#namespaces)
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- [Create namespace](#create-namespace)
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- [Pods](#pods)
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- [Create an pod](#create-an-pod)
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- [Get Pod](#get-pod)
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- [delete Pod](#delete-pod)
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- [OOMKilled](#oomkilled)
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- [Attach to an pod](#attach-to-an-pod)
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- [Run command on pod](#run-command-on-pod)
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- [Persistent volumes](#persistent-volumes)
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- [find persistent volume used pvc](#find-persistent-volume-used-pvc)
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- [Patch pv - change to retain policy](#patch-pv---change-to-retain-policy)
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- [Patch pv - remove finalizers](#patch-pv---remove-finalizers)
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- [kubectl](#kubectl)
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- [Helper pods](#helper-pods)
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- [network testing](#network-testing)
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- [Resources](#resources)
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- [Services Accounts](#services-accounts)
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- [Secrets](#secrets)
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- [Manifest - Opaque / Base64](#manifest---opaque--base64)
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- [Manifest - StringData](#manifest---stringdata)
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- [Inline with heredoc and environment variables](#inline-with-heredoc-and-environment-variables)
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- [substr](#substr)
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- [nodes](#nodes)
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- [taint nodes](#taint-nodes)
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- [control plane - NoSchedule](#control-plane---noschedule)
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- [statefulset](#statefulset)
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- [statefulset - Set Replicas](#statefulset---set-replicas)
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- [Deployment](#deployment)
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- [Deployment - Set Replicas](#deployment---set-replicas)
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- [Deployment - Restart](#deployment---restart)
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- [certs](#certs)
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- [list all certs](#list-all-certs)
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- [get cert end date](#get-cert-end-date)
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- [service accounts](#service-accounts)
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- [core-dns](#core-dns)
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- [Services DNS Name](#services-dns-name)
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- [Custom Resource Definitions](#custom-resource-definitions)
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- [k3s](#k3s)
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- [Install / Setup](#install--setup)
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- [prune old images](#prune-old-images)
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- [check system logs](#check-system-logs)
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- [Workarounds \& Fixes](#workarounds--fixes)
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- [Failed unmounting var-lib-rancher.mount on reboot](#failed-unmounting-var-lib-ranchermount-on-reboot)
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- [klipper-lb](#klipper-lb)
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- [troubleshooting](#troubleshooting)
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## Namespaces
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### Create namespace
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Using cli
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``` bash
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kubectl create namespace tests
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```
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Or using yaml
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``` yaml
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apiVersion: v1
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kind: Namespace
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metadata:
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name: namespace-name
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labels:
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name: namespace-name
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```
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## Pods
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### Create an pod
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**Create an ubuntu pod for tty access example:**
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``` bash
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apiVersion: v1
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kind: Pod
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metadata:
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name: ubuntu-test
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namespace: tests
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spec:
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#### deploy to an specific node
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nodeName: chimera-gluten
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containers:
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- name: ubuntu-test
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image: ubuntu
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# In Kubernetes, the pod stays alive as long as PID 1 is running.
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# so with this options:
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# - It does not exit automatically.
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# - It waits for user input forever.
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# - It behaves like an interactive shell session.
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command: ["sh"] # PID 1 = interactive shell
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stdin: true # keep STDIN open
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tty: true # allocate a terminal
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volumeMounts:
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- name: data
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mountPath: /data
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volumes:
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- name: data
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persistentVolumeClaim:
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claimName: data-pvc
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```
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**Create an ubuntu pod with and execute command:**
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``` bash
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apiVersion: v1
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kind: Pod
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metadata:
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name: ubuntu-ls-test
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namespace: tests
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spec:
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restartPolicy: Never # executes only one time, no retry on error
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#
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# nodeName: "serverExample01" # restrict to an specific node
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#
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containers:
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- name: ubuntu-seaweedfs-test
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image: ubuntu
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command: ["bash", "-c"]
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args:
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- "ls -lah /data"
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volumeMounts:
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- name: data
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mountPath: /data
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volumes:
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- name: data
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persistentVolumeClaim:
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claimName: data-pvc
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```
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### Get Pod
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**Get pod name by label ap:**
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```bash
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POD_NAME=$(kubectl get pod -l app=myAppName -n appNamespace -o jsonpath='{.items[0].metadata.name}')
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echo $POD_NAME
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```
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**Get pod name by text on description, for example find by ip:**
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``` bash
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kubectl get pods -A -o wide | grep 10.0.3.224
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```
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### delete Pod
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``` bash
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kubectl delete pod -n appNamespace -l app=myAppName
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```
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### OOMKilled
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**list all OOMKilled pods:**
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``` bash
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kubectl get events --all-namespaces | grep -i "OOMKilled"
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```
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``` bash
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kubectl get pods --all-namespaces \
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-o jsonpath='{range .items[*]}{.metadata.namespace}{" "}{.metadata.name}{" "}{.status.containerStatuses[*].lastState.terminated.reason}{"\n"}{end}' \
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| grep OOMKilled
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```
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### Attach to an pod
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Attach connects your terminal to the main process of the container (PID 1), or another running process if specified.
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Use it when you want to:
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- see the raw output of the main process
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- want to send input directly to the main process
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``` bash
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kubectl attach -it myPodName -n appNamespace
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```
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``` bash
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POD_NAME=$(kubectl get pod -l app=myAppName -n appNamespace -o jsonpath='{.items[0].metadata.name}')
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kubectl attach -it ${POD_NAME} -n appNamespace
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```
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### Run command on pod
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``` bash
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# sh
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POD_NAME=$(kubectl get pod -l app=myAppName -n appNamespace -o jsonpath='{.items[0].metadata.name}')
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kubectl exec -it ${POD_NAME} -- sh
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```
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``` bash
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# bash
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POD_NAME=$(kubectl get pod -l app=myAppName -n appNamespace -o jsonpath='{.items[0].metadata.name}')
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kubectl exec -it ${POD_NAME} -- bash
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```
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``` bash
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# execute an command like ls
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POD_NAME=$(kubectl get pod -l app=myAppName -n appNamespace -o jsonpath='{.items[0].metadata.name}')
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kubectl exec -it ${POD_NAME} -- ls /
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```
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## Persistent volumes
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### find persistent volume used pvc
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``` bash
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NAMESPACE=???
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PVC_NAME=???
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PV_NAME=$(kubectl get pvc $PVC_NAME -n $NAMESPACE -o jsonpath='{.spec.volumeName}')
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echo "${PV_NAME}"
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```
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### Patch pv - change to retain policy
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``` bash
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PV_NAME="???"
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kubectl patch pv $PV_NAME \
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-p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'
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```
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### Patch pv - remove finalizers
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``` bash
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PV_NAME="???"
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kubectl patch pv $PV_NAME \
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-p '{"metadata":{"finalizers": null}}'
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```
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## kubectl
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kubectl is the command‑line tool used to interact with Kubernetes clusters. Think of it as the “remote control” for Kubernetes: it lets you deploy applications, inspect resources, and manage cluster operations directly from your terminal.
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### Helper pods
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#### network testing
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``` bash
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kubectl run -i --tty dns-test --namespace tests --image=busybox --restart=Never --
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kubectl delete pod dns-test --namespace tests || 0
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```
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**Example using yaml and hostNetwork:**
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- Create Pod
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: dns-test
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namespace: tests
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spec:
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hostNetwork: true
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containers:
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- name: dns-test
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image: busybox
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command: ["sh"]
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stdin: true
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tty: true
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```
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- Attach to Pod
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```bash
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kubectl attach -it dns-test -n tests
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```
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- Execute command inside pod.
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``` bash
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nslookup google.com
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```
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- Delete pod
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```bash
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kubectl delete pod dns-test --namespace tests
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```
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### Resources
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**List all resources:**
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```bash
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kubectl get all -n kube-system | grep traefik
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```
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**List service accounts:**
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```bash
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kubectl get serviceAccount --all-namespaces
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```
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### Services Accounts
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**List all:**
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```bash
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kubectl get serviceAccount --all-namespaces
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```
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**Get Service Account Token:**
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```bash
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kubectl get secret <secret_name> -o jsonpath='{.data.token}' | base64 -d
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```
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```bash
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kubectl get secret <secret_name> -o jsonpath='{.data.token}' | base64 -d > ./service-account-secret-base64
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```
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**Get Cluster certificate Base64:**
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```bash
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kubectl config view --raw -o jsonpath='{.clusters[0].cluster.certificate-authority-data}'
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```
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## Secrets
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### Manifest - Opaque / Base64
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```yaml
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apiVersion: v1
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kind: Secret
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metadata:
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name: secret-name
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namespace: namespace-name
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type: Opaque
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data:
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SERVER_ADDRESS: MTI3LjAuMC4x # 127.0.0.1 BASE64
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```
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### Manifest - StringData
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```yaml
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apiVersion: v1
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kind: Secret
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metadata:
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name: secret-name
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namespace: namespace-name
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stringData:
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SERVER_ADDRESS: 127.0.0.1
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```
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### Inline with heredoc and environment variables
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``` bash
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SERVER_ADDRESS=127.0.0.1
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kubectl apply -f - <<EOF
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apiVersion: v1
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kind: Secret
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metadata:
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name: secret-name
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namespace: namespace-name
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stringData:
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SERVER_ADDRESS: ${SERVER_ADDRESS}
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EOF
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```
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### substr
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**yaml secret template:**
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``` yaml
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# ./secret.yaml
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apiVersion: v1
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kind: Secret
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metadata:
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name: secret-name
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namespace: namespace-name
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stringData:
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SERVER_ADDRESS: ${SERVER_ADDRESS}
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```
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``` bash
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export SERVER_ADDRESS="127.0.1"
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envsubst < ./secret.yaml | kubectl apply -f -
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```
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**env file and envsubst:**
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``` bash
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#---
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# ./.env
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# content:
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# SERVER_ADDRESS=127.0.0.1
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#---
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set -a
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source ./.env
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set +a
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envsubst < ./secret.yaml | kubectl apply -f -
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```
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## nodes
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**Get nodes info:**
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```bash
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kubectl get nodes -o wide
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```
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**get node taints:**
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``` bash
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kubectl describe node <NODE_NAME> | grep taint
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```
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**remove annotation:**
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``` bash
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kubectl annotate node <NODE_NAME> <ANNOTATION_NAME>-
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```
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### taint nodes
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#### control plane - NoSchedule
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``` bash
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MASTER_NODE_NAME="master-node-name"
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kubectl taint nodes ${MASTER_NODE_NAME} node-role.kubernetes.io/control-plane=:NoSchedule
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```
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## statefulset
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### statefulset - Set Replicas
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```bash
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kubectl patch statefulset <statefulset-name> \
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-p '{"spec":{"replicas":0}}'
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```
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## Deployment
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### Deployment - Set Replicas
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``` bash
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DEPLOYMENT_NAME="???"
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# example with 0 to "disable" deployment
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kubectl scale deployment ${DEPLOYMENT_NAME} --replicas=0
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```
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```bash
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kubectl patch deployment <deployment-name> \
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-p '{"spec":{"replicas":0}}'
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```
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### Deployment - Restart
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**example restart coredns:**
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``` bash
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kubectl rollout restart deployment coredns -n kube-system
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```
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## certs
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### list all certs
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```bash
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kubectl get cert -n default
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```
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### get cert end date
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``` bash
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kubectl get secret certificate-name-tls -o "jsonpath={.data['tls\.crt']}" | base64 --decode | openssl x509 -enddate -noout
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```
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## service accounts
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**Get service account token:**
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```bash
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kubectl get secret continuous-deploy -o jsonpath='{.data.token}' | base64 -d
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```
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## core-dns
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Kubernetes automatically provides DNS names for Services and Pods, and CoreDNS serves these records. This allows workloads to communicate using stable, predictable names instead of changing IP addresses.
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### Services DNS Name
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```text
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<service-name>.<namespace>.svc.<cluster-domain>
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```
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Remove warning from logs.
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```log
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[WARNING] No files matching import glob pattern: /etc/coredns/custom/*.server
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[WARNING] No files matching import glob pattern: /etc/coredns/custom/*.override
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```
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1. Apply on kubernetes
|
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```yaml
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apiVersion: v1
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kind: ConfigMap
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metadata:
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name: coredns-custom
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namespace: kube-system
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data:
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log.override: |
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#
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stub.server: |
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#
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```
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|
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## Custom Resource Definitions
|
||
|
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- **Definition:** A Custom Resource Definition (CRD) is an extension of the Kubernetes API.
|
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|
||
- **Purpose:** They allow you to define new resource kinds (e.g., Database, Backup, FooBar) that behave like native Kubernetes objects.
|
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|
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- **Analogy:** By default, Kubernetes understands objects like Pods and Services. With CRDs, you can add your own object types and manage them with kubectl just like built‑in resources
|
||
|
||
**List traefik CRDS:**
|
||
|
||
```bash
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kubectl get crds | grep traefik
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```
|
||
|
||
|
||
## k3s
|
||
|
||
K3s is a lightweight, certified Kubernetes distribution designed to run in resource‑constrained environments such as edge devices, IoT appliances, and small servers. It simplifies installation and operation by packaging Kubernetes into a single small binary, while still being fully compliant with the Kubernetes API.
|
||
|
||
🌐 What K3s Is
|
||
|
||
- Definition: K3s is a simplified Kubernetes distribution created by Rancher Labs (now part of SUSE) and maintained under the CNCF.
|
||
- Purpose: It’s built for environments where full Kubernetes (K8s) is too heavy — like Raspberry Pis, edge servers, or CI pipelines.
|
||
- Size: The entire distribution is packaged into a binary under ~70MB.
|
||
|
||
### Install / Setup
|
||
|
||
**Default master installation:**
|
||
|
||
``` bash
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||
curl -sfL https://get.k3s.io | sh -
|
||
```
|
||
|
||
Install specific version and disable:
|
||
|
||
- flannel (alternative example calico)
|
||
- servicelb (alternative example metallb)
|
||
- traefik (then install using helm chart or custom manifests for better control)
|
||
|
||
```bash
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curl -sfL https://get.k3s.io | INSTALL_K3S_VERSION=v1.33.3+k3s1 INSTALL_K3S_EXEC="--flannel-backend=none \
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||
--disable-network-policy \
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||
--cluster-cidr=10.42.0.0/16 \
|
||
--disable=servicelb \
|
||
--disable=traefik" \
|
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sh -
|
||
```
|
||
|
||
### prune old images
|
||
|
||
prune old images, execute on kubernetes host node
|
||
|
||
```bash
|
||
crictl rmi --prune
|
||
```
|
||
|
||
### check system logs
|
||
|
||
```bash
|
||
sudo journalctl -u k3s-agent --since "1h ago" --reverse --no-pager | more
|
||
sudo journalctl -u k3s-agent --since "1 hour ago" --reverse | grep -i "Starting k3s-agent.service"
|
||
sudo journalctl -u k3s --reverse | grep -i "Starting k3s.service"
|
||
```
|
||
|
||
*Example: [test-services.services.svc.cluster.local](test-services.services.svc.cluster.local).*
|
||
|
||
### Workarounds & Fixes
|
||
|
||
#### Failed unmounting var-lib-rancher.mount on reboot
|
||
|
||
When running K3s with /var/lib/rancher on a separate disk.
|
||
|
||
K3s and containerd often leave behind mount namespaces and overlay layers that block clean unmounting during shutdown.
|
||
This causes slow reboots and errors like:
|
||
|
||
``` bash
|
||
Failed unmounting var-lib-rancher.mount
|
||
```
|
||
|
||
1. Create the cleanup service
|
||
|
||
``` bash
|
||
nano /etc/systemd/system/rancher-cleanup.service
|
||
```
|
||
|
||
Paste:
|
||
|
||
``` bash
|
||
|
||
[Unit]
|
||
DefaultDependencies=no
|
||
Before=shutdown.target
|
||
|
||
[Service]
|
||
Type=oneshot
|
||
ExecStart=/bin/sh -c '/bin/umount -l /var/lib/rancher || true'
|
||
|
||
[Install]
|
||
WantedBy=shutdown.target
|
||
|
||
```
|
||
|
||
Why this works
|
||
|
||
- DefaultDependencies=no ensures the service runs early.
|
||
- Before=umount.target guarantees it executes before systemd tries to unmount anything.
|
||
- umount -l detaches the filesystem immediately, even if containerd still holds namespaces.
|
||
- || true prevents harmless “not mounted” errors from blocking shutdown.
|
||
|
||
1. Reload systemd
|
||
|
||
``` bash
|
||
systemctl daemon-reload
|
||
```
|
||
|
||
1. Enable the cleanup service
|
||
|
||
```bash
|
||
systemctl enable rancher-cleanup.service
|
||
```
|
||
|
||
1. Reboot to test:
|
||
|
||
``` bash
|
||
reboot
|
||
```
|
||
|
||
### klipper-lb
|
||
|
||
Klipper‑LB is the tiny, built‑in load balancer that k3s uses to give each agent a local, stable endpoint for talking to the Kubernetes API server. Instead of exposing a full external load balancer, k3s runs this lightweight component on 127.0.0.1:6444, and it simply forwards traffic from the agent to the control‑plane node (or rotates between multiple servers in an HA setup). It exists to make k3s simpler to deploy—no extra software, and no external LB. startup even though the cluster continues working normally.
|
||
|
||
#### troubleshooting
|
||
|
||
**log: warning - Error starting load balancer: listen tcp 127.0.0.1:6444: bind: address already in use.**
|
||
|
||
``` bash
|
||
rm -rf /var/lib/rancher/k3s/agent/etc/klipper-lb
|
||
systemctl restart k3s-agent
|
||
```
|