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Kubernetes_references.md

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kubernetes

Pod

pod is a object which encapsulates or groups one or more containers (such as Docker containers), with shared storage/network, and a specification for how to run the containers.

below is the basic structure of pod

  apiVersion: v1
  kind: Pod
  metadata:
    name: my-first-app
    labels:
      type: front-end
  spec:
    conatiners:
      - name: busybox
        image: busybox

  • command to list the pods

    kubectl get pods

  • command to create a pod with image busybox ( it actually creates deployment )

    kubectl run my-pod --image=busybox

  • command to delete a particular pod

    kubectl delete pod pod_name

  • if you have created pod using kubectl run command but you want see configrations of pod, so to get yml out of pod use below command

    kubectl get pod pod_name -o yaml > my_pod_file.yaml

  • if you want describe your pod

    kubectl describe pod pod_name

  • if you want to login for running pod

    kubectl exec -it pod_name /bin/sh

  • if you want access logs of any container inside pod

    kubectl logs pod_name -c conatiner_name_inside_pod   ( container name inside pod you will get it by kubectl describe pod command )

  • let's say you have created pod using kubectl run command and now you want to change small configuration of pod then you can use below command

      kubectl edit pod pod_name ( it will open a vi editor , so you can change and save it back then you no need apply 
  it back kubernetes will automatically updates the pod )

  • let's you have created pods in any other namespaces ( other than default ) , to list them use below command

      kubectl get pods --namespace=dev   ( assuming namespace is dev )

ReplicaSet

replicaset is an kubernetes object which is used make your pod highly available and any point time it will make sure sepcified replicas are up and running

basic structure replicaset

     apiVesrion: apps/v1
     kind: ReplicaSet
     metadata: 
       name: my-rs
       lables:
         type: front-end
     spec:
       template:
         metadata:
           name: my-pod
           lables: 
             type: front-end
         spec: 
          containers:
            - name: nginx
              image: nginx 
       replicas: 6
       selector:
         matchLables:
           type: front-end

when you create replica set , it automatically creates pods

  • to list replicaset

      kubectl get rs or kubectl get replicasets

  • to list replicasets in other name space

      kubectl get rs --namespace=dev ( assuming namespace is dev )

  • to delete replicaset

      kubectl delete rs rs_name

  • lets say replica set has been created via kubectl run command , you want to see configuration file of it

      kubectl get rs rs_name -o yaml > rs_sample.yaml

  • lets say you want to edit rs

      kubectl edit rs rs_name ( it opens vi editor and do the changes , save it back it automatically applies it back )
  
 but one thing to keep in mind is lets you have created rs with image busybox777 and replicas 3
 it creates 3 pods with status failed , you will change rs and apply it back
 but even then pods will with old configuration, so here you have 2 options 
 1. delete all old pods and now while creating new pods it will take updated configurations
 2. delete rs and re-create it

  • to increase or decrease replica count without changing rs yaml config file use below command

      kubectl scale rs rs_name --replicas=6