DevOps: Kubernetes Commands

#kubectl run mypod --image=nginx

#kubectl get pods -o wide

#kubectl get pods -o yml

#kubectl get pods -o json

#kubectl explain pods|less --> Provide detail information about POD

#kubectl explain rc|less

#kubectl describe pod <pod-name> -> Provide us pod information

#Try to delete container which is running on worker node

#kubectl get pods

#kubectl delete pod <pod-name>

#kubectl get ns --> It will show us namespaces

Label:

kubectl label pod mypod env=uat

kubectl get pods -o wide

Create POD:

====

K8 Architecture:

=======

K8 Installation using kubeadm

Minikube

============

POD:

A pod is the smallest execution unit in Kubernetes. A pod encapsulates one or more applications. Pods are ephemeral by nature, if a pod (or the node it executes on) fails, Kubernetes can automatically create a new replica of that pod to continue operations.

Create POD

#kubectl run myfirstpod --image=nginx

Delete POD

Syntax: kubectl delete resourcetype resourcename

#kubectl delete pod pod-name

Create POD using YAML file:

---

$ kubectl explain pod

KIND: Pod

VERSION: v1

DESCRIPTION:

Pod is a collection of containers that can run on a host. This resource is

created by clients and scheduled onto hosts.

FIELDS:

apiVersion <string>

APIVersion defines the versioned schema of this representation of an

object. Servers should convert recognized schemas to the latest internal

value, and may reject unrecognized values. More info:

https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources

kind <string>

Kind is a string value representing the REST resource this object

represents. Servers may infer this from the endpoint the client submits

requests to. Cannot be updated. In CamelCase. More info:

https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds

metadata <Object>

Standard object's metadata. More info:

https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata

spec <Object>

Specification of the desired behavior of the pod. More info:

https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

status <Object>

Most recently observed status of the pod. This data may not be up to date.

Populated by the system. Read-only. More info:

https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status

First YAML:

apiVersion: v1

kind: Pod

metadata:

spec:

containers:

- name: mycont

image: httpd

NAME READY STATUS RESTARTS AGE

mypod1 1/1 Running 0 104s

Validate YML file using dry run:

$ kubectl create -f mypod.yml --dry-run

W0909 17:40:59.349555 6142 helpers.go:553] --dry-run is deprecated and can be replaced with --dry-run=client.

pod/mypod1 created (dry run)

$ kubectl explain pod --recursive |less

It will show us field inside yaml file.

$ kubectl explain pod --recursive |head -20

KIND: Pod

VERSION: v1

DESCRIPTION:

Pod is a collection of containers that can run on a host. This resource is

created by clients and scheduled onto hosts.

FIELDS:

apiVersion <string>

kind <string>

metadata <Object>

annotations <map[string]string>

clusterName <string>

creationTimestamp <string>

deletionGracePeriodSeconds <integer>

deletionTimestamp <string>

finalizers <[]string>

generateName <string>

generation <integer>

labels <map[string]string>

Create yaml using command:

kubectl run demopod1 --image=nginx --dry-run -o yaml >test

apiVersion: v1

kind: Pod

metadata:

creationTimestamp: null

labels:

run: demopod1

spec:

containers:

- image: nginx

resources: {}

dnsPolicy: ClusterFirst

restartPolicy: Always

status: {}

Delete POD using YML:

$ kubectl delete -f mypod.yml

pod "mypod1" deleted

=========

edit POD

#kubectl edit pod myfirstpod

--> We can change label details

===================

Create and apply Difference:

Object/Resources creation:

Imperative command: Without using yaml

Imperative Object configuration: #kubectl create -f file-name

If you want to edit configuration then we will use edit command.

#kubectl edit pod mypod

Manually we have to edit configuration.

Declarative Object configuration: #kubectl apply -f file-name

In declarative you have to edit yaml file and then execute apply command once again.

Dry Run:

$ kubectl run demopod --dry-run --image=nginx

W0909 17:08:34.392782 12400 helpers.go:553] --dry-run is deprecated and can be replaced with --dry-run=client.

pod/demopod created (dry run)

#kubectl diff -f mypod.yml

showing difference in yml file

============

Lables:

kubectl label pod mypod env=uat

Selectors:

ReplicationController

ReplicaSet

Scaling

Deployment

Kubernestes Networking

Types of Services

Persistent Volume

Liveness Probe

ConfigMap

Secrets

Namespaces

Resources

Horizontal Pod Autoscaling

Kubernestes Jobs

Init Container

Statefull and Stateless Application

Deploy Webserver

Scale Webserver

Kubernestes Ingress

Deploy Wordpress Website

Attach Persistant Volume to wordpress site

Helm Chart:

$ kubectl get pods

No resources found in default namespace.

$ kubectl run mypod --image=nginx

pod/mypod created

$ kubectl get pods

NAME READY STATUS RESTARTS AGE

mypod 0/1 ContainerCreating 0 6s

$ kubectl get pods

NAME READY STATUS RESTARTS AGE

mypod 1/1 Running 0 12s

$ kubectl describe pod mypod

Name: mypod

Namespace: default

Priority: 0

Node: minikube/10.0.0.6

Start Time: Fri, 09 Sep 2022 16:42:58 +0000

Labels: run=mypod

Annotations: <none>

Status: Running

IP: 172.18.0.3

IPs:

IP: 172.18.0.3

Containers:

mypod:

Container ID: docker://5f49779cfb23fb29db1c660593fe1ba3de027b9a543282cc5498b3170fcf35fb

Image: nginx

Image ID: docker-pullable://nginx@sha256:b95a99feebf7797479e0c5eb5ec0bdfa5d9f504bc94da550c2f58e839ea6914f

Label:

Using metadata tags attached to different resources and objects is a must-have requirement for any Kubernetes (K8s) environment. Kubernetes labels allow DevOps teams to perform in-cluster object searches, apply bulk configuration changes, and more. Labels can help simplify and solve many day-to-day challenges encountered in Kubernetes environments:

Assigning Label to Pod

#kubectl label pod mypod env=dev

$ kubectl describe pod mypod

Name: mypod

Namespace: default

Priority: 0

Node: minikube/10.0.0.6

Start Time: Fri, 09 Sep 2022 16:42:58 +0000

Labels: env=dev

run=mypod

Override Label:

#kubectl label --overwrite pod mypod env=uat

$ kubectl label --overwrite pod mypod env=uat

pod/mypod labeled

$ kubectl describe pod mypod

Name: mypod

Namespace: default

Priority: 0

Node: minikube/10.0.0.6

Start Time: Fri, 09 Sep 2022 16:42:58 +0000

Labels: env=uat

run=mypod

Remove Label:

$ kubectl label pod mypod env-

pod/mypod labeled

$ kubectl describe pod mypod

Name: mypod

Namespace: default

Priority: 0

Node: minikube/10.0.0.6

Start Time: Fri, 09 Sep 2022 16:42:58 +0000

Labels: run=mypod

Assign Label to All Pods in same Namespace:

$ kubectl label pod --all env=dev

pod/mypod labeled

pod/mypod1 labeled

$ kubectl get pods --show-labels

NAME READY STATUS RESTARTS AGE LABELS

mypod 1/1 Running 0 13m env=dev,run=mypod

mypod1 1/1 Running 0 2m33s env=dev,run=mypod1

================

How to set environment variable

apiVersion: v1

kind: Pod

metadata:

labels:

newlbl: test1

spec:

containers:

- name: democpntiner

image: nginx

env:

- name: env_type

value: dev

- name: env_loc

value: apac

Create pod and then check env variable.

#docker container exec -it container-id env

Run command in POD:

#kubectl exec mypod env

#kubectl exec mypod -c mycontainer env --> if we have multiple container inside pod

Create Multi Container POD:

apiVersion: v1

kind: Pod

metadata:

labels:

env: dev

spec:

containers:

- name: con1

image: nginx

- name: con2

image: ubuntu

args: [ "sleep", "3600" ]

==================

#kubectl exec pod-name -c container-name -it bash

==================

Init Container:

In Kubernetes, we can run more than one container in a Pod, but as a practice, we run only one application container. Along with an application container, we can also run one or more init containers.

Kubernetes init containers run in the same Pod as the main application container, though with a separate life cycle. The pattern is often used to initialize a state or configuration for the application running in the main container.

An init container is an additional container in a Pod that completes a task before the "regular" container is started
The regular container will only be started once the init container has been started
An init container in a Pod must run and complete before any other application containers in the Pod start.
This is a great way to initialize a Kubernetes Pod. You can pull any files (keystores, policies, and so forth), configurations, and so on with an init container.
Just as with any other application container, we can have more than one init container in a given Pod; but unlike an application container, each init container must run to completion before the next init container starts.

[root@controller ~]# cat pod-init-container.yml
apiVersion: v1
kind: Pod
metadata:
  name: init-container-example-1
spec:
  initContainers:
  - name: sleepy
    image: alpine
    command: ['sleep', '60']
  containers:
  - name: web
    image: nginx

Sidecar Container:

Typically, there are two different categories of containers: the container that runs the application and another container that provides helper functionality to the primary application.
In the Kubernetes space, the container providing helper functionality is called a sidecar container.
Among the most commonly used capabilities of a sidecar container are file synchronization, logging, and watcher capabilities.
The sidecars are not part of the main traffic or API of the primary application. They usually operate asynchronously and are not involved in the public API.
A great example is a central logging agent. Your main container can just log to stdout, but the sidecar container will send all logs to a central logging service where they will be aggregated with the logs from the entire system.

[root@controller ~]# cat example-1.yaml
apiVersion: v1
kind: Pod
metadata:
  name: sidecar-pod-1
spec:
  volumes:
  - name: log
    emptyDir: {}

  containers:
  - image: busybox
    name: application
    args:
     - /bin/sh
     - -c
     - >
      while true; do
        echo "$(date) INFO hello" >> /var/log/myapp.log ;
        sleep 1;
      done
    volumeMounts:
    - name: log
      mountPath: /var/log

  - name: sidecar
    image: busybox
    args:
     - /bin/sh
     - -c
     - tail -fn+1 /var/log/myapp.log
    volumeMounts:
    - name: log
      mountPath: /var/log

======================

===============

$ kubectl --help

kubectl controls the Kubernetes cluster manager.

Find more information at: https://kubernetes.io/docs/reference/kubectl/overview/

Basic Commands (Beginner):

create Create a resource from a file or from stdin.

expose Take a replication controller, service, deployment or pod and expose it as a new Kubernetes Service

run Run a particular image on the cluster

set Set specific features on objects

Basic Commands (Intermediate):

explain Documentation of resources

get Display one or many resources

edit Edit a resource on the server

delete Delete resources by filenames, stdin, resources and names, or by resources and label selector

Deploy Commands:

rollout Manage the rollout of a resource

scale Set a new size for a Deployment, ReplicaSet or Replication Controller

autoscale Auto-scale a Deployment, ReplicaSet, or ReplicationController

Cluster Management Commands:

certificate Modify certificate resources.

cluster-info Display cluster info

top Display Resource (CPU/Memory/Storage) usage.

cordon Mark node as unschedulable

uncordon Mark node as schedulable

drain Drain node in preparation for maintenance

taint Update the taints on one or more nodes

Troubleshooting and Debugging Commands:

describe Show details of a specific resource or group of resources

logs Print the logs for a container in a pod

attach Attach to a running container

exec Execute a command in a container

port-forward Forward one or more local ports to a pod

proxy Run a proxy to the Kubernetes API server

cp Copy files and directories to and from containers.

auth Inspect authorization

debug Create debugging sessions for troubleshooting workloads and nodes

Advanced Commands:

diff Diff live version against would-be applied version

apply Apply a configuration to a resource by filename or stdin

patch Update field(s) of a resource

replace Replace a resource by filename or stdin

wait Experimental: Wait for a specific condition on one or many resources.

kustomize Build a kustomization target from a directory or a remote url.

Settings Commands:

label Update the labels on a resource

annotate Update the annotations on a resource

completion Output shell completion code for the specified shell (bash or zsh)

Other Commands:

api-resources Print the supported API resources on the server

api-versions Print the supported API versions on the server, in the form of "group/version"

config Modify kubeconfig files

plugin Provides utilities for interacting with plugins.

version Print the client and server version information

Important Blogs:

Kubernetes Create Pod using Kubectl and YAML Tutorial (progressivecoder.com)

Create Kubernestes POD using YAML file:

Create A Pod In Kubernetes Cluster | by Bharathiraja | CodeX | Medium

Secret:

Pull an Image from a Private Registry | Kubernetes

DevOps

Friday, September 9, 2022

Kubernetes Commands

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